diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index f3f3fbe6d..b1d4e6b1b 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -1310,6 +1310,27 @@ UT_011_03:
     - ESP32_IDF
     - EMMC
 
+UT_012_01:
+  <<: *unit_test_template
+  tags:
+    - ESP32_IDF
+    - UT_T1_1
+    - 8Mpsram
+
+UT_012_02:
+  <<: *unit_test_template
+  tags:
+    - ESP32_IDF
+    - UT_T1_1
+    - 8Mpsram
+
+UT_012_03:
+  <<: *unit_test_template
+  tags:
+    - ESP32_IDF
+    - UT_T1_1
+    - 8Mpsram
+
 UT_601_01:
   <<: *unit_test_template
   tags:
diff --git a/components/esp32/CMakeLists.txt b/components/esp32/CMakeLists.txt
index 007a6c435..c1b7c6e38 100644
--- a/components/esp32/CMakeLists.txt
+++ b/components/esp32/CMakeLists.txt
@@ -19,6 +19,7 @@ else()
 
     set(COMPONENT_SRCS "brownout.c"
                    "cache_err_int.c"
+                   "cache_sram_mmu.c"
                    "clk.c"
                    "coexist.c"
                    "core_dump.c"
@@ -30,6 +31,7 @@ else()
                    "esp_err_to_name.c"
                    "esp_timer.c"
                    "esp_timer_esp32.c"
+                   "esp_himem.c"
                    "ets_timer_legacy.c"
                    "event_default_handlers.c"
                    "event_loop.c"
diff --git a/components/esp32/Kconfig b/components/esp32/Kconfig
index 8402caecc..edfea9c5a 100644
--- a/components/esp32/Kconfig
+++ b/components/esp32/Kconfig
@@ -67,15 +67,24 @@ endchoice
 
 choice SPIRAM_TYPE
     prompt "Type of SPI RAM chip in use"
-    default SPIRAM_TYPE_ESPPSRAM32
+    default SPIRAM_TYPE_AUTO
+
+config SPIRAM_TYPE_AUTO
+    bool "Auto-detect"
 
 config SPIRAM_TYPE_ESPPSRAM32
     bool "ESP-PSRAM32 or IS25WP032"
+
+config SPIRAM_TYPE_ESPPSRAM64
+    bool "ESP-PSRAM64 or LY68L6400"
+
 endchoice
 
 config SPIRAM_SIZE
     int
+    default -1 if SPIRAM_TYPE_AUTO
     default 4194304 if SPIRAM_TYPE_ESPPSRAM32
+    default 8388608 if SPIRAM_TYPE_ESPPSRAM64
     default 0
 
 choice SPIRAM_SPEED
@@ -120,6 +129,29 @@ config SPIRAM_CACHE_WORKAROUND
         This will also not use any bits of newlib that are located in ROM, opting for a version that is compiled
         with the workaround and located in flash instead.
 
+config SPIRAM_BANKSWITCH_ENABLE
+    bool "Enable bank switching for >4MiB external RAM"
+    default y
+    depends on SPIRAM_USE_MEMMAP || SPIRAM_USE_CAPS_ALLOC || SPIRAM_USE_MALLOC
+    help
+        The ESP32 only supports 4MiB of external RAM in its address space. The hardware does support larger
+        memories, but these have to be bank-switched in and out of this address space. Enabling this allows you
+        to reserve some MMU pages for this, which allows the use of the esp_himem api to manage these banks.
+
+#Note that this is limited to 62 banks, as esp_spiram_writeback_cache needs some kind of mapping of some banks
+#below that mark to work. We cannot at this moment guarantee this to exist when himem is enabled.
+config SPIRAM_BANKSWITCH_RESERVE
+    int "Amount of 32K pages to reserve for bank switching"
+    depends on SPIRAM_BANKSWITCH_ENABLE
+    default 8
+    range 1 62
+    help
+        Select the amount of banks reserved for bank switching. Note that the amount of RAM allocatable with 
+        malloc/esp_heap_alloc_caps will decrease by 32K for each page reserved here.
+        
+        Note that this reservation is only actually done if your program actually uses the himem API. Without
+        any himem calls, the reservation is not done and the original amount of memory will be available
+        to malloc/esp_heap_alloc_caps.
 
 config SPIRAM_MALLOC_ALWAYSINTERNAL
     int "Maximum malloc() size, in bytes, to always put in internal memory"
diff --git a/components/esp32/cache_sram_mmu.c b/components/esp32/cache_sram_mmu.c
new file mode 100644
index 000000000..6be8a1dee
--- /dev/null
+++ b/components/esp32/cache_sram_mmu.c
@@ -0,0 +1,141 @@
+// Copyright 2010-2018 Espressif Systems (Shanghai) PTE LTD
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <stdint.h>
+#include "soc/soc.h"
+#include "soc/dport_reg.h"
+#include "string.h"
+#include "esp_spi_flash.h"
+
+//Errors that can be returned
+#define MMU_SET_ADDR_ALIGNED_ERROR 1
+#define MMU_SET_PAGE_SIZE_ERROR 3
+#define MMU_SET_VADDR_OUT_RANGE 5
+
+
+#define PROCACHE_MMU_ADDR_BASE 0x3FF10000
+#define APPCACHE_MMU_ADDR_BASE 0x3FF12000
+
+
+//sram
+#define PRO_DRAM1_START_ADDR   0x3F800000
+#define PRO_DRAM1_END_ADDR(psize)     (PRO_DRAM1_START_ADDR + ((psize) << 17))
+//cache mmu register file address
+#define CACHE_MMU_ADDRESS_BASE(cpu_no) ((cpu_no) ? (APPCACHE_MMU_ADDR_BASE) : (PROCACHE_MMU_ADDR_BASE))
+//virtual address, physical address check
+#define ADDRESS_CHECK(addr,psize) (((addr) & (0xFFFF >>((64/(psize))-1))) != 0)
+//CPU number check
+#define CPU_NUMBER_CHECK(cpu_no)  (((cpu_no)<0) || ((cpu_no)>1))
+//PID check
+#define PID_CHECK(pid)  (((pid)<0) || ((pid)>7))
+//flash MMU edge check (flash size default : 16*1024 K)
+#define FLASH_MMU_EDGE_CHECK(mmu_val,num) (((mmu_val) + (num)) > 256)
+//sram MMU edge check (sram size default : 8*1024 K)
+#define SRAM_MMU_EDGE_CHECK(mmu_val,num,psize) (((mmu_val) + (num)) > ((8*1024)/(psize)))
+
+//We can relegate to the ROM version if the 2nd core isn't running (yet) and the RTOS is not started yet, for instance
+//in the bootloader and in the app start process. The ROM code manually disables the cache, without using
+//cache guards.
+unsigned int cache_sram_mmu_set_rom(int cpu_no, int pid, unsigned int vaddr, unsigned int paddr, int psize, int num);
+
+
+#ifndef BOOTLOADER_BUILD
+
+/*
+Note that this function is a replacement for the ROM function with the same name, with these differences:
+- It uses the DPORT workarounds
+- It fixes a bug where the ROM version throws an error when vaddr is more than 2MiB into the memory region
+- It uses the SPI cache guards to make sure the MMU is idle
+*/
+unsigned int IRAM_ATTR cache_sram_mmu_set(int cpu_no, int pid, unsigned int vaddr, unsigned int paddr, int psize, int num)
+{
+    const spi_flash_guard_funcs_t *guard=spi_flash_guard_get();
+    if (!guard) {
+        //Still starting up; guards not available yet. Use ROM version of code.
+        return cache_sram_mmu_set_rom(cpu_no, pid, vaddr, paddr, psize, num);
+    }
+
+    unsigned int i,shift,mask_s;
+    unsigned int mmu_addr;
+    unsigned int mmu_table_val;
+    //address check 
+    if( (ADDRESS_CHECK(vaddr,psize)) || (ADDRESS_CHECK(paddr,psize)) ){
+        return MMU_SET_ADDR_ALIGNED_ERROR;
+    }
+    //psize check 
+    if(psize == 32) {
+        shift  = 15;
+        mask_s = 0;
+    } else if(psize == 16) {
+        shift  = 14;
+        mask_s = 1;
+    } else if(psize == 8) {
+        shift  = 13;
+        mask_s = 2;
+    } else if(psize == 4) {
+        shift  = 12;
+        mask_s = 3;
+    } else if(psize == 2) {
+        shift  = 11;
+        mask_s = 4;
+    } else {
+        return MMU_SET_PAGE_SIZE_ERROR;
+    }
+    //mmu value
+    mmu_table_val = paddr >> shift;
+    //mmu_addr 
+    if(pid == 0 || pid == 1){
+        if(vaddr >= PRO_DRAM1_START_ADDR && vaddr < PRO_DRAM1_END_ADDR(psize)){
+            mmu_addr = 1152 + ((vaddr & (0x3FFFFF >> mask_s)) >> shift);
+        } else{
+            return MMU_SET_VADDR_OUT_RANGE;
+        }
+    } else {
+        if(vaddr >= PRO_DRAM1_START_ADDR && vaddr < PRO_DRAM1_END_ADDR(psize)){
+            mmu_addr = (1024 + (pid<<7)) + ((vaddr & (0x3FFFFF >> mask_s)) >> shift);
+        } else{
+            return MMU_SET_VADDR_OUT_RANGE;
+        }
+    }
+
+    //The MMU registers are implemented in such a way that lookups from the cache subsystem may collide with
+    //CPU access to the MMU registers. We use the flash guards to make sure the cache is disabled.
+    guard->start();
+
+    //mmu change
+    for ( i = 0; i < num; i++){
+        *(volatile unsigned int *)(CACHE_MMU_ADDRESS_BASE(cpu_no) + mmu_addr * 4) = mmu_table_val + i; //write table
+        mmu_addr++;
+    }
+
+    if(cpu_no == 0){
+        DPORT_REG_SET_FIELD(DPORT_PRO_CACHE_CTRL1_REG, DPORT_PRO_CMMU_SRAM_PAGE_MODE, mask_s);
+    } else {
+        DPORT_REG_SET_FIELD(DPORT_APP_CACHE_CTRL1_REG, DPORT_APP_CMMU_SRAM_PAGE_MODE, mask_s);
+    }
+
+    guard->end();
+
+    return 0;
+}
+
+
+#else
+
+//For the bootloader, we can always use the ROM version of this: it works well enough and keeps the size of the bootloader binary down.
+unsigned int cache_sram_mmu_set(int cpu_no, int pid, unsigned int vaddr, unsigned int paddr, int psize, int num) {
+    return cache_sram_mmu_set_rom(cpu_no, pid, vaddr, paddr, psize, num);
+}
+
+#endif
diff --git a/components/esp32/esp_himem.c b/components/esp32/esp_himem.c
new file mode 100644
index 000000000..89e5b3237
--- /dev/null
+++ b/components/esp32/esp_himem.c
@@ -0,0 +1,366 @@
+// Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "freertos/FreeRTOS.h"
+#include "freertos/task.h"
+#include "esp_spiram.h"
+#include "rom/cache.h"
+#include "sdkconfig.h"
+#include "esp_himem.h"
+#include "soc/soc.h"
+#include "esp_log.h"
+
+/*
+So, why does the API look this way and is so inflexible to not allow any maps beyond the full 32K chunks? Most of
+it has to do with the fact that the cache works on the *virtual* addresses What this comes down to is that while it's
+allowed to map a range of physical memory into the address space two times, there's no cache consistency between the
+two regions.
+
+This means that a write to region A may or may not show up, perhaps delayed, in region B, as it depends on
+the time that the writeback to SPI RAM is done on A and the time before the corresponding cache line is invalidated
+on B. Note that this goes for every 32-byte cache line: this implies that if a program writes to address X and Y within
+A, the write to Y may show up before the write to X does.
+
+It gets even worse when both A and B are written: theoretically, a write to a 32-byte cache line in A can be entirely
+undone because of a write to a different addres in B that happens to be in the same 32-byte cache line.
+
+Because of these reasons, we do not allow double mappings at all. This, however, has other implications that make
+supporting ranges not really useful. Because the lack of double mappings, applications will need to do their own
+management of mapped regions, meaning they will normally map in and out blocks at a time anyway, as mapping more
+fluent regions would result in the chance of accidentally mapping two overlapping regions. As this is the case,
+to keep the code simple, at the moment we just force these blocks to be equal to the 32K MMU page size. The API
+itself does allow for more granular allocations, so if there's a pressing need for a more complex solution in the
+future, we can do this.
+
+Note: In the future, we can expand on this api to do a memcpy() between SPI RAM and (internal) memory using the SPI1
+peripheral. This needs support for SPI1 to be in the SPI driver, however.
+*/
+
+#if CONFIG_SPIRAM_BANKSWITCH_ENABLE
+#define SPIRAM_BANKSWITCH_RESERVE CONFIG_SPIRAM_BANKSWITCH_RESERVE
+#else
+#define SPIRAM_BANKSWITCH_RESERVE 0
+#endif
+
+#define CACHE_BLOCKSIZE (32*1024)
+
+//Start of the virtual address range reserved for himem use
+#define VIRT_HIMEM_RANGE_START (SOC_EXTRAM_DATA_LOW+(128-SPIRAM_BANKSWITCH_RESERVE)*CACHE_BLOCKSIZE)
+//Start MMU block reserved for himem use
+#define VIRT_HIMEM_RANGE_BLOCKSTART (128-SPIRAM_BANKSWITCH_RESERVE)
+//Start physical block
+#define PHYS_HIMEM_BLOCKSTART (128-SPIRAM_BANKSWITCH_RESERVE)
+
+#define TAG "esp_himem"
+
+#define HIMEM_CHECK(cond, str, err) if (cond) do {ESP_LOGE(TAG, "%s: %s", __FUNCTION__, str); return err; } while(0)
+
+// Metadata for a block of physical RAM
+typedef struct {
+    unsigned int is_alloced: 1;
+    unsigned int is_mapped: 1;
+} ramblock_t;
+
+//Metadata for a 32-K memory address range
+typedef struct {
+    unsigned int is_alloced: 1;
+    unsigned int is_mapped: 1;
+    unsigned int ram_block: 16;
+} rangeblock_t;
+
+static ramblock_t *s_ram_descriptor = NULL;
+static rangeblock_t *s_range_descriptor = NULL;
+static int s_ramblockcnt = 0;
+static const int s_rangeblockcnt = SPIRAM_BANKSWITCH_RESERVE;
+
+//Handle for a window of address space
+typedef struct esp_himem_rangedata_t {
+    int block_ct;
+    int block_start;
+} esp_himem_rangedata_t;
+
+//Handle for a range of physical memory
+typedef struct esp_himem_ramdata_t {
+    int block_ct;
+    uint16_t *block;
+} esp_himem_ramdata_t;
+
+static portMUX_TYPE spinlock = portMUX_INITIALIZER_UNLOCKED;
+
+static inline int ramblock_idx_valid(int ramblock_idx)
+{
+    return (ramblock_idx >= 0 && ramblock_idx < s_ramblockcnt);
+}
+
+static inline int rangeblock_idx_valid(int rangeblock_idx)
+{
+    return (rangeblock_idx >= 0 && rangeblock_idx < s_rangeblockcnt);
+}
+
+static void set_bank(int virt_bank, int phys_bank, int ct)
+{
+    int r;
+    r = cache_sram_mmu_set( 0, 0, SOC_EXTRAM_DATA_LOW + CACHE_BLOCKSIZE * virt_bank, phys_bank * CACHE_BLOCKSIZE, 32, ct );
+    assert(r == 0);
+    r = cache_sram_mmu_set( 1, 0, SOC_EXTRAM_DATA_LOW + CACHE_BLOCKSIZE * virt_bank, phys_bank * CACHE_BLOCKSIZE, 32, ct );
+    assert(r == 0);
+}
+
+size_t esp_himem_get_phys_size()
+{
+    int paddr_start = (4096 * 1024) - (CACHE_BLOCKSIZE * SPIRAM_BANKSWITCH_RESERVE);
+    return esp_spiram_get_size()-paddr_start;
+}
+
+size_t esp_himem_get_free_size()
+{
+    size_t ret=0;
+    for (int i = 0; i < s_ramblockcnt; i++) {
+        if (!s_ram_descriptor[i].is_alloced) ret+=CACHE_BLOCKSIZE;
+    }
+    return ret;
+}
+
+size_t esp_himem_reserved_area_size() {
+    return CACHE_BLOCKSIZE * SPIRAM_BANKSWITCH_RESERVE;
+}
+
+
+void __attribute__((constructor)) esp_himem_init()
+{
+    if (SPIRAM_BANKSWITCH_RESERVE == 0) return;
+    int maxram=esp_spiram_get_size();
+    //catch double init
+    HIMEM_CHECK(s_ram_descriptor != NULL, "already initialized", ); //Looks weird; last arg is empty so it expands to 'return ;'
+    HIMEM_CHECK(s_range_descriptor != NULL, "already initialized", );
+    //need to have some reserved banks
+    HIMEM_CHECK(SPIRAM_BANKSWITCH_RESERVE == 0, "No banks reserved for himem", );
+    //Start and end of physical reserved memory. Note it starts slightly under
+    //the 4MiB mark as the reserved banks can't have an unity mapping to be used by malloc
+    //anymore; we treat them as himem instead.
+    int paddr_start = (4096 * 1024) - (CACHE_BLOCKSIZE * SPIRAM_BANKSWITCH_RESERVE);
+    int paddr_end = maxram;
+    s_ramblockcnt = ((paddr_end - paddr_start) / CACHE_BLOCKSIZE);
+    //Allocate data structures
+    s_ram_descriptor = calloc(sizeof(ramblock_t), s_ramblockcnt);
+    s_range_descriptor = calloc(sizeof(rangeblock_t), SPIRAM_BANKSWITCH_RESERVE);
+    if (s_ram_descriptor == NULL || s_range_descriptor == NULL) {
+        ESP_EARLY_LOGE(TAG, "Cannot allocate memory for meta info. Not initializing!");
+        free(s_ram_descriptor);
+        free(s_range_descriptor);
+        return;
+    }
+    ESP_EARLY_LOGI(TAG, "Initialized. Using last %d 32KB address blocks for bank switching on %d KB of physical memory.", 
+                SPIRAM_BANKSWITCH_RESERVE, (paddr_end - paddr_start)/1024);
+}
+
+
+//Allocate count not-necessarily consecutive physical RAM blocks, return numbers in blocks[]. Return
+//true if blocks can be allocated, false if not.
+static bool allocate_blocks(int count, uint16_t *blocks_out)
+{
+    int n = 0;
+    for (int i = 0; i < s_ramblockcnt && n != count; i++) {
+        if (!s_ram_descriptor[i].is_alloced) {
+            blocks_out[n] = i;
+            n++;
+        }
+    }
+    if (n == count) {
+        //All blocks could be allocated. Mark as in use.
+        for (int i = 0; i < count; i++) {
+            s_ram_descriptor[blocks_out[i]].is_alloced = true;
+            assert(s_ram_descriptor[blocks_out[i]].is_mapped == false);
+        }
+        return true;
+    } else {
+        //Error allocating blocks
+        return false;
+    }
+}
+
+
+esp_err_t esp_himem_alloc(size_t size, esp_himem_handle_t *handle_out)
+{
+    if (size % CACHE_BLOCKSIZE != 0) {
+        return ESP_ERR_INVALID_SIZE;
+    }
+    int blocks = size / CACHE_BLOCKSIZE;
+    esp_himem_ramdata_t *r = calloc(sizeof(esp_himem_ramdata_t), 1);
+    if (!r) {
+        goto nomem;
+    }
+    r->block = calloc(sizeof(uint16_t), blocks);
+    if (!r->block) {
+        goto nomem;
+    }
+    portENTER_CRITICAL(&spinlock);
+    int ok = allocate_blocks(blocks, r->block);
+    portEXIT_CRITICAL(&spinlock);
+    if (!ok) {
+        goto nomem;
+    }
+    r->block_ct = blocks;
+    *handle_out = r;
+    return ESP_OK;
+nomem:
+    if (r) {
+        free(r->block);
+    }
+    free(r);
+    return ESP_ERR_NO_MEM;
+}
+
+esp_err_t esp_himem_free(esp_himem_handle_t handle)
+{
+    //Check if any of the blocks is still mapped; fail if this is the case.
+    for (int i = 0; i < handle->block_ct; i++) {
+        assert(ramblock_idx_valid(handle->block[i]));
+        HIMEM_CHECK(s_ram_descriptor[handle->block[i]].is_mapped, "block in range still mapped", ESP_ERR_INVALID_ARG);
+    }
+    //Mark blocks as free
+    portENTER_CRITICAL(&spinlock);
+    for (int i = 0; i < handle->block_ct; i++) {
+        s_ram_descriptor[handle->block[i]].is_alloced = false;
+    }
+    portEXIT_CRITICAL(&spinlock);
+
+    //Free handle
+    free(handle->block);
+    free(handle);
+    return ESP_OK;
+}
+
+
+esp_err_t esp_himem_alloc_map_range(size_t size, esp_himem_rangehandle_t *handle_out)
+{
+    HIMEM_CHECK(s_ram_descriptor == NULL, "Himem not available!", ESP_ERR_INVALID_STATE);
+    HIMEM_CHECK(size % CACHE_BLOCKSIZE != 0, "requested size not aligned to blocksize", ESP_ERR_INVALID_SIZE);
+    int blocks = size / CACHE_BLOCKSIZE;
+    esp_himem_rangedata_t *r = calloc(sizeof(esp_himem_rangedata_t), 1);
+    if (!r) {
+        return ESP_ERR_NO_MEM;
+    }
+    r->block_ct = blocks;
+    r->block_start = -1;
+    int start_free = 0;
+    portENTER_CRITICAL(&spinlock);
+    for (int i = 0; i < s_rangeblockcnt; i++) {
+        if (s_range_descriptor[i].is_alloced) {
+            start_free = i + 1; //optimistically assume next block is free...
+        } else if (i - start_free == blocks - 1) {
+            //We found a span of blocks that's big enough to allocate the requested range in.
+            r->block_start = start_free;
+            break;
+        }
+    }
+
+    if (r->block_start == -1) {
+        //Couldn't find enough free blocks
+        free(r);
+        portEXIT_CRITICAL(&spinlock);
+        return ESP_ERR_NO_MEM;
+    }
+    //Range is found. Mark the blocks as in use.
+    for (int i = 0; i < blocks; i++) {
+        s_range_descriptor[r->block_start + i].is_alloced = 1;
+    }
+    portEXIT_CRITICAL(&spinlock);
+    //All done.
+    *handle_out = r;
+    return ESP_OK;
+}
+
+esp_err_t esp_himem_free_map_range(esp_himem_rangehandle_t handle)
+{
+    //Check if any of the blocks in the range have a mapping
+    for (int i = 0; i < handle->block_ct; i++) {
+        assert(rangeblock_idx_valid(handle->block_start + i));
+        assert(s_range_descriptor[i + handle->block_start].is_alloced == 1); //should be, if handle is valid
+        HIMEM_CHECK(s_range_descriptor[i + handle->block_start].is_mapped, "memory still mapped to range", ESP_ERR_INVALID_ARG);
+    }
+    //We should be good to free this. Mark blocks as free.
+    portENTER_CRITICAL(&spinlock);
+    for (int i = 0; i < handle->block_ct; i++) {
+        s_range_descriptor[i + handle->block_start].is_alloced = 0;
+    }
+    portEXIT_CRITICAL(&spinlock);
+    free(handle);
+    return ESP_OK;
+}
+
+
+esp_err_t esp_himem_map(esp_himem_handle_t handle, esp_himem_rangehandle_t range, size_t ram_offset, size_t range_offset, size_t len, int flags, void **out_ptr)
+{
+    int ram_block = ram_offset / CACHE_BLOCKSIZE;
+    int range_block = range_offset / CACHE_BLOCKSIZE;
+    int blockcount = len / CACHE_BLOCKSIZE;
+    HIMEM_CHECK(s_ram_descriptor == NULL, "Himem not available!", ESP_ERR_INVALID_STATE);
+    //Offsets and length must be block-aligned
+    HIMEM_CHECK(ram_offset % CACHE_BLOCKSIZE != 0, "ram offset not aligned to blocksize", ESP_ERR_INVALID_ARG);
+    HIMEM_CHECK(range_offset % CACHE_BLOCKSIZE != 0, "range not aligned to blocksize", ESP_ERR_INVALID_ARG);
+    HIMEM_CHECK(len % CACHE_BLOCKSIZE != 0, "length not aligned to blocksize", ESP_ERR_INVALID_ARG);
+    //ram and range should be within allocated range
+    HIMEM_CHECK(ram_block + blockcount > handle->block_ct, "args not in range of phys ram handle", ESP_ERR_INVALID_SIZE);
+    HIMEM_CHECK(range_block + blockcount > range->block_ct, "args not in range of range handle", ESP_ERR_INVALID_SIZE);
+
+    //Check if ram blocks aren't already mapped, and if memory range is unmapped
+    for (int i = 0; i < blockcount; i++) {
+        HIMEM_CHECK(s_ram_descriptor[handle->block[i + ram_block]].is_mapped, "ram already mapped", ESP_ERR_INVALID_STATE);
+        HIMEM_CHECK(s_range_descriptor[range->block_start + i + range_block].is_mapped, "range already mapped", ESP_ERR_INVALID_STATE);
+    }
+
+    //Map and mark as mapped
+    portENTER_CRITICAL(&spinlock);
+    for (int i = 0; i < blockcount; i++) {
+        assert(ramblock_idx_valid(handle->block[i + ram_block]));
+        s_ram_descriptor[handle->block[i + ram_block]].is_mapped = 1;
+        s_range_descriptor[range->block_start + i + range_block].is_mapped = 1;
+        s_range_descriptor[range->block_start + i + range_block].ram_block = handle->block[i + ram_block];
+    }
+    portEXIT_CRITICAL(&spinlock);
+    for (int i = 0; i < blockcount; i++) {
+        set_bank(VIRT_HIMEM_RANGE_BLOCKSTART + range->block_start + i + range_block, handle->block[i + ram_block] + PHYS_HIMEM_BLOCKSTART, 1);
+    }
+
+    //Set out pointer
+    *out_ptr = (void *)(VIRT_HIMEM_RANGE_START + (range->block_start + range_offset) * CACHE_BLOCKSIZE);
+    return ESP_OK;
+}
+
+esp_err_t esp_himem_unmap(esp_himem_rangehandle_t range, void *ptr, size_t len)
+{
+    //Note: doesn't actually unmap, just clears cache and marks blocks as unmapped.
+    //Future optimization: could actually lazy-unmap here: essentially, do nothing and only clear the cache when we re-use
+    //the block for a different physical address.
+    int range_offset = (uint32_t)ptr - VIRT_HIMEM_RANGE_START;
+    int range_block = (range_offset / CACHE_BLOCKSIZE) - range->block_start;
+    int blockcount = len / CACHE_BLOCKSIZE;
+    HIMEM_CHECK(range_offset % CACHE_BLOCKSIZE != 0, "range offset not block-aligned", ESP_ERR_INVALID_ARG);
+    HIMEM_CHECK(len % CACHE_BLOCKSIZE != 0, "map length not block-aligned", ESP_ERR_INVALID_ARG);
+    HIMEM_CHECK(range_block + blockcount > range->block_ct, "range out of bounds for handle", ESP_ERR_INVALID_ARG);
+
+    portENTER_CRITICAL(&spinlock);
+    for (int i = 0; i < blockcount; i++) {
+        int ramblock = s_range_descriptor[range->block_start + i + range_block].ram_block;
+        assert(ramblock_idx_valid(ramblock));
+        s_ram_descriptor[ramblock].is_mapped = 0;
+        s_range_descriptor[range->block_start + i + range_block].is_mapped = 0;
+    }
+    esp_spiram_writeback_cache();
+    portEXIT_CRITICAL(&spinlock);
+    return ESP_OK;
+}
+
+
diff --git a/components/esp32/include/esp_himem.h b/components/esp32/include/esp_himem.h
new file mode 100644
index 000000000..099d92601
--- /dev/null
+++ b/components/esp32/include/esp_himem.h
@@ -0,0 +1,152 @@
+// Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+#pragma once
+
+#include <stddef.h>
+#include "esp_err.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+//Opaque pointers as handles for ram/range data
+typedef struct esp_himem_ramdata_t *esp_himem_handle_t;
+typedef struct esp_himem_rangedata_t *esp_himem_rangehandle_t;
+
+//ESP32 MMU block size
+#define ESP_HIMEM_BLKSZ (0x8000)
+
+#define ESP_HIMEM_MAPFLAG_RO 1 /*!< Indicates that a mapping will only be read from. Note that this is unused for now. */
+
+/**
+ * @brief Allocate a block in high memory
+ *
+ * @param size Size of the to-be-allocated block, in bytes. Note that this needs to be
+ *             a multiple of the external RAM mmu block size (32K).
+ * @param[out] handle_out Handle to be returned
+ * @returns - ESP_OK if succesful
+ *          - ESP_ERR_NO_MEM if out of memory
+ *          - ESP_ERR_INVALID_SIZE if size is not a multiple of 32K
+ */
+esp_err_t esp_himem_alloc(size_t size, esp_himem_handle_t *handle_out);
+
+
+/**
+ * @brief Allocate a memory region to map blocks into
+ * 
+ * This allocates a contiguous CPU memory region that can be used to map blocks
+ * of physical memory into.
+ *
+ * @param size Size of the range to be allocated. Note this needs to be a multiple of
+ *             the external RAM mmu block size (32K).
+ * @param[out] handle_out Handle to be returned
+ * @returns - ESP_OK if succesful
+ *          - ESP_ERR_NO_MEM if out of memory or address space
+ *          - ESP_ERR_INVALID_SIZE if size is not a multiple of 32K
+ */
+esp_err_t esp_himem_alloc_map_range(size_t size, esp_himem_rangehandle_t *handle_out);
+
+/**
+ * @brief Map a block of high memory into the CPUs address space
+ *
+ * This effectively makes the block available for read/write operations.
+ * 
+ * @note The region to be mapped needs to have offsets and sizes that are aligned to the
+ *       SPI RAM MMU block size (32K)
+ *
+ * @param handle Handle to the block of memory, as given by esp_himem_alloc
+ * @param range Range handle to map the memory in
+ * @param ram_offset Offset into the block of physical memory of the block to map
+ * @param range_offset Offset into the address range where the block will be mapped
+ * @param len Length of region to map
+ * @param flags One of ESP_HIMEM_MAPFLAG_*
+ * @param[out] out_ptr Pointer to variable to store resulting memory pointer in
+ * @returns - ESP_OK if the memory could be mapped
+ *          - ESP_ERR_INVALID_ARG if offset, range or len aren't MMU-block-aligned (32K)
+ *          - ESP_ERR_INVALID_SIZE if the offsets/lengths don't fit in the allocated memory or range
+ *          - ESP_ERR_INVALID_STATE if a block in the selected ram offset/length is already mapped, or
+ *                                  if a block in the selected range offset/length already has a mapping.
+ */
+esp_err_t esp_himem_map(esp_himem_handle_t handle, esp_himem_rangehandle_t range, size_t ram_offset, size_t range_offset, size_t len, int flags, void **out_ptr);
+
+
+/**
+ * @brief Free a block of physical memory
+ *
+ * This clears out the associated handle making the memory available for re-allocation again.
+ * This will only succeed if none of the memory blocks currently have a mapping.
+ *
+ * @param handle Handle to the block of memory, as given by esp_himem_alloc
+ * @returns - ESP_OK if the memory is succesfully freed
+ *          - ESP_ERR_INVALID_ARG if the handle still is (partially) mapped
+ */
+esp_err_t esp_himem_free(esp_himem_handle_t handle);
+
+
+
+/**
+ * @brief Free a mapping range
+ *
+ * This clears out the associated handle making the range available for re-allocation again.
+ * This will only succeed if none of the range blocks currently are used for a mapping.
+ *
+ * @param handle Handle to the range block, as given by esp_himem_alloc_map_range
+ * @returns - ESP_OK if the memory is succesfully freed
+ *          - ESP_ERR_INVALID_ARG if the handle still is (partially) mapped to
+ */
+esp_err_t esp_himem_free_map_range(esp_himem_rangehandle_t handle);
+
+
+/**
+ * @brief Unmap a region
+ *
+ * @param range Range handle
+ * @param ptr Pointer returned by esp_himem_map
+ * @param len Length of the block to be unmapped. Must be aligned to the SPI RAM MMU blocksize (32K)
+ * @returns - ESP_OK if the memory is succesfully unmapped,
+ *          - ESP_ERR_INVALID_ARG if ptr or len are invalid.
+ */
+esp_err_t esp_himem_unmap(esp_himem_rangehandle_t range, void *ptr, size_t len);
+
+
+/**
+ * @brief Get total amount of memory under control of himem API
+ *
+ * @returns Amount of memory, in bytes
+ */
+size_t esp_himem_get_phys_size();
+
+/**
+ * @brief Get free amount of memory under control of himem API
+ *
+ * @returns Amount of free memory, in bytes
+ */
+size_t esp_himem_get_free_size();
+
+
+/**
+ * @brief Get amount of SPI memory address space needed for bankswitching
+ *
+ * @note This is also weakly defined in esp32/spiram.c and returns 0 there, so
+ *       if no other function in this file is used, no memory is reserved.
+ *
+ * @returns Amount of reserved area, in bytes
+ */
+size_t esp_himem_reserved_area_size();
+
+
+#ifdef __cplusplus
+}
+#endif
+
diff --git a/components/esp32/include/rom/cache.h b/components/esp32/include/rom/cache.h
index 72aa33aaa..4b923e669 100644
--- a/components/esp32/include/rom/cache.h
+++ b/components/esp32/include/rom/cache.h
@@ -83,6 +83,9 @@ static inline unsigned int IRAM_ATTR cache_flash_mmu_set(int cpu_no, int pid, un
   * @brief Set Ext-SRAM-Cache mmu mapping.
   *        Please do not call this function in your SDK application.
   *
+  * Note that this code lives in IRAM and has a bugfix in respect to the ROM version
+  * of this function (which erroneously refused a vaddr > 2MiB
+  *
   * @param  int cpu_no : CPU number, 0 for PRO cpu, 1 for APP cpu.
   *
   * @param  int pod : process identifier. Range 0~7.
@@ -106,18 +109,7 @@ static inline unsigned int IRAM_ATTR cache_flash_mmu_set(int cpu_no, int pid, un
   *                   4 : mmu table to be written is out of range
   *                   5 : vaddr is out of range
   */
-static inline unsigned int IRAM_ATTR cache_sram_mmu_set(int cpu_no, int pid, unsigned int vaddr, unsigned int paddr, int psize, int num)
-{
-    extern unsigned int cache_sram_mmu_set_rom(int cpu_no, int pid, unsigned int vaddr, unsigned int paddr, int psize, int num);
-
-    unsigned int ret;
-
-    DPORT_STALL_OTHER_CPU_START();
-    ret = cache_sram_mmu_set_rom(cpu_no, pid, vaddr, paddr, psize, num);
-    DPORT_STALL_OTHER_CPU_END();
-
-    return ret;
-}
+unsigned int IRAM_ATTR cache_sram_mmu_set(int cpu_no, int pid, unsigned int vaddr, unsigned int paddr, int psize, int num);
 
 /**
   * @brief Initialise cache access for the cpu.
diff --git a/components/esp32/spiram.c b/components/esp32/spiram.c
index 5345c5a37..58360aa0e 100644
--- a/components/esp32/spiram.c
+++ b/components/esp32/spiram.c
@@ -34,6 +34,7 @@ we add more types of external RAM memory, this can be made into a more intellige
 #include "soc/soc_memory_layout.h"
 #include "soc/dport_reg.h"
 #include "rom/cache.h"
+#include "esp_himem.h"
 
 #if CONFIG_FREERTOS_UNICORE
 #define PSRAM_MODE PSRAM_VADDR_MODE_NORMAL
@@ -65,6 +66,22 @@ extern int _ext_ram_bss_start, _ext_ram_bss_end;
 static bool spiram_inited=false;
 
 
+//If no function in esp_himem.c is used, this function will be linked into the
+//binary instead of the one in esp_himem.c, automatically making sure no memory
+//is reserved if no himem function is used.
+size_t __attribute__((weak)) esp_himem_reserved_area_size() {
+    return 0;
+}
+
+
+static int spiram_size_usable_for_malloc()
+{
+    int s=esp_spiram_get_size();
+    if (s>4*1024*1024) s=4*1024*1024; //we can map at most 4MiB
+    return s-esp_himem_reserved_area_size();
+}
+
+
 /*
  Simple RAM test. Writes a word every 32 bytes. Takes about a second to complete for 4MiB. Returns
  true when RAM seems OK, false when test fails. WARNING: Do not run this before the 2nd cpu has been
@@ -74,7 +91,7 @@ bool esp_spiram_test()
 {
     volatile int *spiram=(volatile int*)SOC_EXTRAM_DATA_LOW;
     size_t p;
-    size_t s=CONFIG_SPIRAM_SIZE;
+    size_t s=spiram_size_usable_for_malloc();
     int errct=0;
     int initial_err=-1;
     for (p=0; p<(s/sizeof(int)); p+=8) {
@@ -109,7 +126,7 @@ void IRAM_ATTR esp_spiram_init_cache()
 esp_spiram_size_t esp_spiram_get_chip_size()
 {
     if (!spiram_inited) {
-        ESP_LOGE(TAG, "SPI RAM not initialized");
+        ESP_EARLY_LOGE(TAG, "SPI RAM not initialized");
         return ESP_SPIRAM_SIZE_INVALID;
     }
     psram_size_t psram_size = psram_get_size();
@@ -134,6 +151,16 @@ esp_err_t esp_spiram_init()
         return r;
     }
 
+    spiram_inited=true; //note: this needs to be set before esp_spiram_get_chip_*/esp_spiram_get_size calls
+#if (CONFIG_SPIRAM_SIZE != -1)
+    if (esp_spiram_get_size()!=CONFIG_SPIRAM_SIZE) {
+        ESP_EARLY_LOGE(TAG, "Expected %dKiB chip but found %dKiB chip. Bailing out..", CONFIG_SPIRAM_SIZE/1024, esp_spiram_get_size()/1024);
+        return ESP_ERR_INVALID_SIZE;
+    }
+#endif
+
+    ESP_EARLY_LOGI(TAG, "Found %dMBit SPI RAM device", 
+                                          (esp_spiram_get_size()*8)/(1024*1024));
     ESP_EARLY_LOGI(TAG, "SPI RAM mode: %s", PSRAM_SPEED == PSRAM_CACHE_F40M_S40M ? "flash 40m sram 40m" : \
                                           PSRAM_SPEED == PSRAM_CACHE_F80M_S40M ? "flash 80m sram 40m" : \
                                           PSRAM_SPEED == PSRAM_CACHE_F80M_S80M ? "flash 80m sram 80m" : "ERROR");
@@ -141,21 +168,20 @@ esp_err_t esp_spiram_init()
                                           (PSRAM_MODE==PSRAM_VADDR_MODE_EVENODD)?"even/odd (2-core)": \
                                           (PSRAM_MODE==PSRAM_VADDR_MODE_LOWHIGH)?"low/high (2-core)": \
                                           (PSRAM_MODE==PSRAM_VADDR_MODE_NORMAL)?"normal (1-core)":"ERROR");
-    spiram_inited=true;
     return ESP_OK;
 }
 
 
 esp_err_t esp_spiram_add_to_heapalloc()
-{   
+{
     //Add entire external RAM region to heap allocator. Heap allocator knows the capabilities of this type of memory, so there's
     //no need to explicitly specify them.
 #if CONFIG_SPIRAM_ALLOW_BSS_SEG_EXTERNAL_MEMORY
-    ESP_EARLY_LOGI(TAG, "Adding pool of %dK of external SPI memory to heap allocator", (CONFIG_SPIRAM_SIZE - (&_ext_ram_bss_end - &_ext_ram_bss_start))/1024);
-    return heap_caps_add_region((intptr_t)&_ext_ram_bss_end, (intptr_t)SOC_EXTRAM_DATA_LOW + CONFIG_SPIRAM_SIZE-1);
+    ESP_EARLY_LOGI(TAG, "Adding pool of %dK of external SPI memory to heap allocator", (spiram_size_usable_for_malloc() - (&_ext_ram_bss_end - &_ext_ram_bss_start))/1024);
+    return heap_caps_add_region((intptr_t)&_ext_ram_bss_end, (intptr_t)SOC_EXTRAM_DATA_LOW + spiram_size_usable_for_malloc()-1);
 #else
-    ESP_EARLY_LOGI(TAG, "Adding pool of %dK of external SPI memory to heap allocator", CONFIG_SPIRAM_SIZE/1024);
-    return heap_caps_add_region((intptr_t)SOC_EXTRAM_DATA_LOW, (intptr_t)SOC_EXTRAM_DATA_LOW + CONFIG_SPIRAM_SIZE-1);
+    ESP_EARLY_LOGI(TAG, "Adding pool of %dK of external SPI memory to heap allocator", spiram_size_usable_for_malloc()/1024);
+    return heap_caps_add_region((intptr_t)SOC_EXTRAM_DATA_LOW, (intptr_t)SOC_EXTRAM_DATA_LOW + spiram_size_usable_for_malloc()-1);
 #endif
 }
 
@@ -187,12 +213,17 @@ esp_err_t esp_spiram_reserve_dma_pool(size_t size) {
 
 size_t esp_spiram_get_size()
 {
+    psram_size_t size=esp_spiram_get_chip_size();
+    if (size==PSRAM_SIZE_32MBITS) return 4*1024*1024;
+    if (size==PSRAM_SIZE_64MBITS) return 8*1024*1024;
     return CONFIG_SPIRAM_SIZE;
 }
 
 /*
  Before flushing the cache, if psram is enabled as a memory-mapped thing, we need to write back the data in the cache to the psram first,
  otherwise it will get lost. For now, we just read 64/128K of random PSRAM memory to do this.
+ Note that this routine assumes some unique mapping for the first 2 banks of the PSRAM memory range, as well as the
+ 2 banks after the 2 MiB mark.
 */
 void IRAM_ATTR esp_spiram_writeback_cache() 
 {
@@ -216,18 +247,24 @@ void IRAM_ATTR esp_spiram_writeback_cache()
     }
 #endif
 
-#if CONFIG_FREERTOS_UNICORE
+#if (PSRAM_MODE != PSRAM_VADDR_MODE_LOWHIGH)
+    /*
+    Single-core and even/odd mode only have 32K of cache evenly distributed over the address lines. We can clear
+    the cache by just reading 64K worth of cache lines.
+    */.
     for (x=0; x<1024*64; x+=32) {
         i+=psram[x];
     }
 #else
     /*
+    Low/high psram cache mode uses one 32K cache for the lowest 2MiB of SPI flash and another 32K for the highest 
+    2MiB. Clear this by reading from both regions.
     Note: this assumes the amount of external RAM is >2M. If it is 2M or less, what this code does is undefined. If 
     we ever support external RAM chips of 2M or smaller, this may need adjusting.
     */
     for (x=0; x<1024*64; x+=32) {
         i+=psram[x];
-        i+=psram[x+(1024*1024*2)+(1024*64)]; //address picked to also clear cache of app cpu in low/high mode
+        i+=psram[x+(1024*1024*2)];
     }
 #endif
 
@@ -243,6 +280,4 @@ void IRAM_ATTR esp_spiram_writeback_cache()
 #endif
 }
 
-
-
 #endif
diff --git a/components/esp32/test/test_himem.c b/components/esp32/test/test_himem.c
new file mode 100644
index 000000000..95ed27d5a
--- /dev/null
+++ b/components/esp32/test/test_himem.c
@@ -0,0 +1,104 @@
+#include "unity.h"
+#include <stdio.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include "freertos/FreeRTOS.h"
+#include "freertos/task.h"
+#include "esp_system.h"
+#include "rom/cache.h"
+#include "sdkconfig.h"
+#include "esp_himem.h"
+
+#if CONFIG_SPIRAM_BANKSWITCH_ENABLE
+
+//Fill memory with pseudo-random data generated from the given seed.
+static void fill_mem_seed(int seed, void *mem, int len)
+{
+    uint32_t *p = (uint32_t *)mem;
+    unsigned int rseed = seed ^ 0xa5a5a5a5;
+    for (int i = 0; i < len / 4; i++) {
+        *p++ = rand_r(&rseed);
+    }
+}
+
+//Check the memory filled by fill_mem_seed. Returns true if the data is still intact.
+static bool check_mem_seed(int seed, void *mem, int len)
+{
+    uint32_t *p = (uint32_t *)mem;
+    unsigned int rseed = seed ^ 0xa5a5a5a5;
+    for (int i = 0; i < len / 4; i++) {
+        uint32_t ex = rand_r(&rseed);
+        if (ex != *p) {
+            printf("check_mem_seed: %p @ %p has 0x%08x expected 0x%08x\n", mem, p, *p, ex);
+            return false;
+        }
+        p++;
+    }
+    return true;
+}
+
+//Allocate a himem region, fill it with data, check it and release it.
+static bool test_region(int check_size, int seed)
+{
+    esp_himem_handle_t mh;
+    esp_himem_rangehandle_t rh;
+    bool ret = true;
+
+    ESP_ERROR_CHECK(esp_himem_alloc(check_size, &mh));
+    ESP_ERROR_CHECK(esp_himem_alloc_map_range(ESP_HIMEM_BLKSZ * 2, &rh));
+    for (int i = 0; i < check_size; i += ESP_HIMEM_BLKSZ) {
+        uint32_t *ptr = NULL;
+        ESP_ERROR_CHECK(esp_himem_map(mh, rh, i, 0, ESP_HIMEM_BLKSZ, 0, (void**)&ptr));
+        fill_mem_seed(i ^ seed, ptr, ESP_HIMEM_BLKSZ);
+        ESP_ERROR_CHECK(esp_himem_unmap(rh, ptr, ESP_HIMEM_BLKSZ));
+    }
+    for (int i = 0; i < check_size; i += ESP_HIMEM_BLKSZ) {
+        uint32_t *ptr;
+        ESP_ERROR_CHECK(esp_himem_map(mh, rh, i, 0, ESP_HIMEM_BLKSZ, 0, (void**)&ptr));
+        if (!check_mem_seed(i ^ seed, ptr, ESP_HIMEM_BLKSZ)) {
+            printf("Error in block %d\n", i / ESP_HIMEM_BLKSZ);
+            ret = false;
+            break;
+        }
+        ESP_ERROR_CHECK(esp_himem_unmap(rh, ptr, ESP_HIMEM_BLKSZ));
+    }
+    ESP_ERROR_CHECK(esp_himem_free(mh));
+    ESP_ERROR_CHECK(esp_himem_free_map_range(rh));
+    return ret;
+}
+
+
+static volatile int testsDone;
+
+static void memtest_thread(void *arg)
+{
+    int d = (int)arg;
+    for (int i = 0; i < 4; i++) {
+        printf("d=%d check=%d\n", d, i);
+        test_region(2 * 1024 * 1024, d + (i << 16));
+        vTaskDelay(d);
+    }
+    testsDone++; //note possible race here... not really an issue if the two tasks have different vTaskDelay args
+    vTaskDelete(NULL);
+}
+
+
+TEST_CASE("high psram memory test", "[himem]")
+{
+    printf("Doing single-core test\n");
+    assert(test_region(4 * 1024 * 1024, 0xaaaa));
+
+    testsDone = 0;
+    printf("Doing dual-core test...\n");
+    xTaskCreatePinnedToCore(&memtest_thread, "th2", 1024 * 2, (void *)2, 5, NULL, 1);
+    xTaskCreatePinnedToCore(&memtest_thread, "th1", 1024 * 2, (void *)5, 5, NULL, 0);
+    while (testsDone != 2) {
+        vTaskDelay(10);
+    }
+
+    printf("Done!\n");
+    vTaskDelay(100);
+}
+
+
+#endif
diff --git a/docs/Doxyfile b/docs/Doxyfile
index 4765c675c..3820e35c5 100644
--- a/docs/Doxyfile
+++ b/docs/Doxyfile
@@ -147,6 +147,8 @@ INPUT = \
     ../../components/heap/include/esp_heap_trace.h \
     ../../components/heap/include/esp_heap_caps_init.h \
     ../../components/heap/include/multi_heap.h \
+    ## Himem
+    ../../components/esp32/include/esp_himem.h \
     ## Interrupt Allocation
     ../../components/esp32/include/esp_intr_alloc.h \
     ## Watchdogs
diff --git a/docs/en/api-reference/system/himem.rst b/docs/en/api-reference/system/himem.rst
new file mode 100644
index 000000000..a3eba8be3
--- /dev/null
+++ b/docs/en/api-reference/system/himem.rst
@@ -0,0 +1,33 @@
+The himem allocation API
+========================
+
+Overview
+--------
+
+The ESP32 can access external SPI RAM transparently, so you can use it as normal memory in your program code. However, because the address
+space for external memory is limited in size, only the first 4MiB can be used as such. Access to the remaining memory is still possible,
+however this needs to go through a bankswitching scheme controlled by the himem API.
+
+Specifically, what is implemented by the himem API is a bankswitching scheme. Hardware-wise, the 4MiB region for external SPI RAM is 
+mapped into the CPU address space by a MMU, which maps a configurable 32K bank/page of external SPI RAM into each of the 32K pages in the
+4MiB region accessed by the CPU. For external memories that are <=4MiB, this MMU is configured to unity mapping, effectively mapping each
+CPU address 1-to-1 to the external SPI RAM address.
+
+In order to use the himem API, you have to enable it in the menuconfig using :envvar:`CONFIG_SPIRAM_BANKSWITCH_ENABLE`, as well as set the amount 
+of banks reserved for this in :envvar:`CONFIG_SPIRAM_BANKSWITCH_RESERVE`. This decreases
+the amount of external memory allocated by functions like ``malloc()``, but it allows you to use the himem api to map any of the remaining memory
+into the reserved banks.
+
+The himem API is more-or-less an abstraction of the bankswitching scheme: it allows you to claim one or more banks of address space
+(called 'regions' in the API) as well as one or more of banks of memory to map into the ranges.
+
+Example
+-------
+
+An example doing a simple memory test of the high memory range is available in esp-idf: :example:`system/himem`
+
+
+API Reference
+-------------
+
+.. include:: /_build/inc/esp_himem.inc
diff --git a/docs/en/api-reference/system/index.rst b/docs/en/api-reference/system/index.rst
index 76b7c8d62..c85b238eb 100644
--- a/docs/en/api-reference/system/index.rst
+++ b/docs/en/api-reference/system/index.rst
@@ -8,6 +8,7 @@ System API
    FreeRTOS Additions <freertos_additions>
    Heap Memory Allocation <mem_alloc>
    Heap Memory Debugging <heap_debug>
+   Himem (large external SPI RAM) API <himem>
    Interrupt Allocation <intr_alloc>
    Watchdogs <wdts>
    Inter-Processor Call <ipc>
diff --git a/docs/en/api-reference/system/mem_alloc.rst b/docs/en/api-reference/system/mem_alloc.rst
index 7d56bf195..62a322bd8 100644
--- a/docs/en/api-reference/system/mem_alloc.rst
+++ b/docs/en/api-reference/system/mem_alloc.rst
@@ -40,6 +40,9 @@ which it can't do for a normal malloc() call. This can help to use all the avail
 Memory allocated with MALLOC_CAP_32BIT can *only* be accessed via 32-bit reads and writes, any other type of access will
 generate a fatal LoadStoreError exception.
 
+External SPI RAM under 4MiB in size can be allocated using standard ``malloc`` calls, if that is enabled in menuconfig. To
+use the region above the 4MiB limit, you can use the :doc:`himem API</api-reference/system/himem>`.
+
 API Reference - Heap Allocation
 -------------------------------
 
diff --git a/docs/zh_CN/api-reference/system/himem.rst b/docs/zh_CN/api-reference/system/himem.rst
new file mode 100644
index 000000000..e34272742
--- /dev/null
+++ b/docs/zh_CN/api-reference/system/himem.rst
@@ -0,0 +1 @@
+.. include:: ../../../en/api-reference/system/himem.rst
\ No newline at end of file
diff --git a/examples/system/himem/CMakeLists.txt b/examples/system/himem/CMakeLists.txt
new file mode 100644
index 000000000..4297397b6
--- /dev/null
+++ b/examples/system/himem/CMakeLists.txt
@@ -0,0 +1,6 @@
+# The following lines of boilerplate have to be in your project's CMakeLists
+# in this exact order for cmake to work correctly
+cmake_minimum_required(VERSION 3.5)
+
+include($ENV{IDF_PATH}/tools/cmake/project.cmake)
+project(himem_test)
diff --git a/examples/system/himem/Makefile b/examples/system/himem/Makefile
new file mode 100644
index 000000000..6ffdebd26
--- /dev/null
+++ b/examples/system/himem/Makefile
@@ -0,0 +1,9 @@
+#
+# This is a project Makefile. It is assumed the directory this Makefile resides in is a
+# project subdirectory.
+#
+
+PROJECT_NAME := himem_test
+
+include $(IDF_PATH)/make/project.mk
+
diff --git a/examples/system/himem/README.md b/examples/system/himem/README.md
new file mode 100644
index 000000000..700df059f
--- /dev/null
+++ b/examples/system/himem/README.md
@@ -0,0 +1,5 @@
+# Example: himem
+
+This test tests the upper memory of an ESP32 system with 8MiB of PSRAM 
+attached. Note that this (obviously) will not work unless the ESP32 
+you're running this on actually does have 8MiB pf PSRAM.
diff --git a/examples/system/himem/main/CMakeLists.txt b/examples/system/himem/main/CMakeLists.txt
new file mode 100644
index 000000000..a875dec50
--- /dev/null
+++ b/examples/system/himem/main/CMakeLists.txt
@@ -0,0 +1,4 @@
+set(COMPONENT_SRCS "himem_test_main.c")
+set(COMPONENT_ADD_INCLUDEDIRS ".")
+
+register_component()
diff --git a/examples/system/himem/main/component.mk b/examples/system/himem/main/component.mk
new file mode 100644
index 000000000..44bd2b527
--- /dev/null
+++ b/examples/system/himem/main/component.mk
@@ -0,0 +1,3 @@
+#
+# Main Makefile. This is basically the same as a component makefile.
+#
diff --git a/examples/system/himem/main/himem_test_main.c b/examples/system/himem/main/himem_test_main.c
new file mode 100644
index 000000000..c5f8c97a2
--- /dev/null
+++ b/examples/system/himem/main/himem_test_main.c
@@ -0,0 +1,98 @@
+/* Himem API example
+
+   This example code is in the Public Domain (or CC0 licensed, at your option.)
+
+   Unless required by applicable law or agreed to in writing, this
+   software is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
+   CONDITIONS OF ANY KIND, either express or implied.
+*/
+#include <stdio.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include "freertos/FreeRTOS.h"
+#include "freertos/task.h"
+#include "freertos/queue.h"
+#include "esp_system.h"
+#include "nvs_flash.h"
+#include "esp_heap_caps.h"
+#include "esp_spiram.h"
+#include "rom/cache.h"
+#include "sdkconfig.h"
+#include "esp_himem.h"
+
+
+//Fill memory with pseudo-random data generated from the given seed.
+//Fills the memory in 32-bit words for speed.
+static void fill_mem_seed(int seed, void *mem, int len)
+{
+    uint32_t *p = (uint32_t *)mem;
+    unsigned int rseed = seed ^ 0xa5a5a5a5;
+    for (int i = 0; i < len / 4; i++) {
+        *p++ = rand_r(&rseed);
+    }
+}
+
+//Check the memory filled by fill_mem_seed. Returns true if the data matches the data
+//that fill_mem_seed wrote (when given the same seed).
+//Returns true if there's a match, false when the region differs from what should be there.
+static bool check_mem_seed(int seed, void *mem, int len, int phys_addr)
+{
+    uint32_t *p = (uint32_t *)mem;
+    unsigned int rseed = seed ^ 0xa5a5a5a5;
+    for (int i = 0; i < len / 4; i++) {
+        uint32_t ex = rand_r(&rseed);
+        if (ex != *p) {
+            printf("check_mem_seed: %x has 0x%08x expected 0x%08x\n", phys_addr+((char*)p-(char*)mem), *p, ex);
+            return false;
+        }
+        p++;
+    }
+    return true;
+}
+
+//Allocate a himem region, fill it with data, check it and release it.
+static bool test_region(int check_size, int seed)
+{
+    esp_himem_handle_t mh; //Handle for the address space we're using
+    esp_himem_rangehandle_t rh; //Handle for the actual RAM.
+    bool ret = true;
+
+    //Allocate the memory we're going to check.
+    ESP_ERROR_CHECK(esp_himem_alloc(check_size, &mh));
+    //Allocate a block of address range
+    ESP_ERROR_CHECK(esp_himem_alloc_map_range(ESP_HIMEM_BLKSZ, &rh));
+    for (int i = 0; i < check_size; i += ESP_HIMEM_BLKSZ) {
+        uint32_t *ptr = NULL;
+        //Map in block, write pseudo-random data, unmap block.
+        ESP_ERROR_CHECK(esp_himem_map(mh, rh, i, 0, ESP_HIMEM_BLKSZ, 0, (void**)&ptr));
+        fill_mem_seed(i ^ seed, ptr, ESP_HIMEM_BLKSZ); //
+        ESP_ERROR_CHECK(esp_himem_unmap(rh, ptr, ESP_HIMEM_BLKSZ));
+    }
+    vTaskDelay(5); //give the OS some time to do things so the task watchdog doesn't bark
+    for (int i = 0; i < check_size; i += ESP_HIMEM_BLKSZ) {
+        uint32_t *ptr;
+        //Map in block, check against earlier written pseudo-random data, unmap block.
+        ESP_ERROR_CHECK(esp_himem_map(mh, rh, i, 0, ESP_HIMEM_BLKSZ, 0, (void**)&ptr));
+        if (!check_mem_seed(i ^ seed, ptr, ESP_HIMEM_BLKSZ, i)) {
+            printf("Error in block %d\n", i / ESP_HIMEM_BLKSZ);
+            ret = false;
+        }
+        ESP_ERROR_CHECK(esp_himem_unmap(rh, ptr, ESP_HIMEM_BLKSZ));
+        if (!ret) break; //don't check rest of blocks if error occurred
+    }
+    //Okay, all done!
+    ESP_ERROR_CHECK(esp_himem_free(mh));
+    ESP_ERROR_CHECK(esp_himem_free_map_range(rh));
+    return ret;
+}
+
+
+void app_main()
+{
+    size_t memcnt=esp_himem_get_phys_size();
+    size_t memfree=esp_himem_get_free_size();
+    printf("Himem has %dKiB of memory, %dKiB of which is free. Testing the free memory...\n", (int)memcnt/1024, (int)memfree/1024);
+    assert(test_region(memfree, 0xaaaa));
+    printf("Done!\n");
+}
+
diff --git a/examples/system/himem/sdkconfig.defaults b/examples/system/himem/sdkconfig.defaults
new file mode 100644
index 000000000..b33372a2c
--- /dev/null
+++ b/examples/system/himem/sdkconfig.defaults
@@ -0,0 +1,12 @@
+CONFIG_SPIRAM_SUPPORT=y
+CONFIG_SPIRAM_BOOT_INIT=y
+CONFIG_SPIRAM_IGNORE_NOTFOUND=
+CONFIG_SPIRAM_USE_MALLOC=y
+CONFIG_SPIRAM_TYPE_AUTO=y
+CONFIG_SPIRAM_SIZE=-1
+CONFIG_SPIRAM_SPEED_40M=y
+CONFIG_SPIRAM_MEMTEST=y
+CONFIG_SPIRAM_CACHE_WORKAROUND=y
+CONFIG_SPIRAM_BANKSWITCH_ENABLE=y
+CONFIG_SPIRAM_BANKSWITCH_RESERVE=4
+
diff --git a/tools/unit-test-app/configs/psram b/tools/unit-test-app/configs/psram
index 4575118a4..03380b2d4 100644
--- a/tools/unit-test-app/configs/psram
+++ b/tools/unit-test-app/configs/psram
@@ -1,2 +1,3 @@
 TEST_EXCLUDE_COMPONENTS=libsodium bt app_update
-CONFIG_SPIRAM_SUPPORT=y
\ No newline at end of file
+CONFIG_SPIRAM_SUPPORT=y
+CONFIG_SPIRAM_BANKSWITCH_ENABLE=n
diff --git a/tools/unit-test-app/configs/psram_8m b/tools/unit-test-app/configs/psram_8m
new file mode 100644
index 000000000..d28e58702
--- /dev/null
+++ b/tools/unit-test-app/configs/psram_8m
@@ -0,0 +1,4 @@
+TEST_COMPONENTS=esp32
+CONFIG_SPIRAM_SUPPORT=y
+CONFIG_SPIRAM_BANKSWITCH_ENABLE=y
+CONFIG_SPIRAM_BANKSWITCH_RESERVE=8
diff --git a/tools/unit-test-app/tools/ConfigDependency.yml b/tools/unit-test-app/tools/ConfigDependency.yml
index 3af3e565b..f7b265bc2 100644
--- a/tools/unit-test-app/tools/ConfigDependency.yml
+++ b/tools/unit-test-app/tools/ConfigDependency.yml
@@ -1 +1,2 @@
-"psram": "CONFIG_SPIRAM_SUPPORT=y"
+"psram": '{CONFIG_SPIRAM_SUPPORT=y} and not {CONFIG_SPIRAM_BANKSWITCH_ENABLE=y}'
+"8Mpsram": "CONFIG_SPIRAM_BANKSWITCH_ENABLE=y"