doc(sdio_slave): add descriptions about conflicts on MTDI pin

docs/en/api-reference/peripherals/sd_pullup_requirements.rst

@@ -0,0 +1,153 @@
+SD Pullup Requirements
+======================
+
+CMD and DATA lines D0-D3 of the slave should be pulled up by 50KOhm resistor
+even in 1-bit mode or SPI mode. The pullups of the slave cards should be
+connected even if they're not connected to the host.
+
+The MTDI strapping pin is incompatible with DAT2 line pull-up by default
+when the code flash is 3.3V. See :ref:`mtdi_strapping_pin` below.
+
+Pullup inside Official Modules
+------------------------------
+
+For Espressif official modules, different weak pullups / pulldowns are
+connected to CMD, and DATA pins as below. To use these modules,
+these pins are required to be pulled up by 50KOhm resistors, since internal
+weak pullups are insufficient.
+
++-----------------------+-----+--------------------------+------+----------------------+------+
+| GPIO                  | 15  | 2                        | 4    | 12                   | 13   |
++=======================+=====+==========================+======+======================+======+
+| Name                  | CMD | DAT0                     | DAT1 | DAT2                 | DAT3 |
++-----------------------+-----+--------------------------+------+----------------------+------+
+| At startup            | WPU | WPD                      | WPD  | PU for 1.8v flash;   | WPU  |
+|                       |     |                          |      | WPD for 3.3v flash   |      |
++-----------------------+-----+--------------------------+------+----------------------+------+
+| Strapping requirement |     | Low to download to flash |      | High for 1.8v flash; |      |
+|                       |     |                          |      | Low for 3.3v flash   |      |
++-----------------------+-----+--------------------------+------+----------------------+------+
+
+- WPU: Weak pullup
+- WPD: Weak pulldown
+- PU: Pullup inside the module
+
+For Wrover modules, they use 1.8v flash, and have pullup on GPIO12 inside.
+For Wroom-32 Series, PICO-D4 modules, they use 3.3v flash, and is weakly
+pulled down internally. See :ref:`mtdi_strapping_pin` below.
+
+Pullup on Official Devkit (WroverKit)
+--------------------------------------
+
+For official Wrover Kit (till version 3), some of the pullups are provided on
+the board as the table below. For other devkits that don't have pullups,
+please connect them yourselves.
+
++-----------------------+-----+------+------+------+---------+
+| GPIO                  | 15  | 2    | 4    | 12   | 13      |
++=======================+=====+======+======+======+=========+
+| Name                  | CMD | DAT0 | DAT1 | DAT2 | DAT3    |
++-----------------------+-----+------+------+------+---------+
+| Pullup on the Kit     | PU  | PU   | PU   |      | PU & PD |
++-----------------------+-----+------+------+------+---------+
+
+- PU: Pullup
+- PD: Pulldown
+
+The DAT3 pullup conflicts with JTAG pulldown in WroverKit v3 and earlier, please
+either:
+
+1. pull it up by resistor less than 5KOhm (2kOhm suggested) in 4-bit mode.
+2. pull it up or drive it high by host or VDD3.3V in 1-bit mode.
+
+.. _mtdi_strapping_pin:
+
+MTDI strapping pin
+------------------
+
+MTDI (GPIO12) is used as a bootstrapping pin to select output voltage of an
+internal regulator which powers the flash chip (VDD_SDIO). This pin has an
+internal pulldown so if left unconnected it will read low at reset (selecting
+default 3.3V operation). When adding a pullup to this pin for SD card
+operation, consider the following:
+
+- For boards which don't use the internal regulator (VDD_SDIO) to power the
+  flash, GPIO12 can be pulled high.
+- For boards which use 1.8V flash chip, GPIO12 needs to be pulled high at
+  reset. This is fully compatible with SD card operation.
+- On boards which use the internal regulator and a 3.3V flash chip, GPIO12
+  must be low at reset. This is incompatible with SD card operation. Please
+  check the table below to see whether your modules/kits use 3.3v flash.
+
++-----------------+---------------+--------------------------------------+
+| Module          | Flash voltage | DAT2 connections                     |
++=================+===============+======================================+
+| PICO-D4         | 3.3V          | Internal PD, change EFUSE and pullup |
++-----------------+               + or disable DAT2 line*                +
+| Wroom-32 Series |               |                                      |
++-----------------+---------------+--------------------------------------+
+| Wrover          | 1.8V          | Internal PU, pullup suggested        |
++-----------------+---------------+--------------------------------------+
+
+Official devkits of different types and version mount different types of
+modules, please refer to the table below to see whether your devkit can
+support SDIO slave without steps above.
+
++--------------------------+-----------------+---------------+
+| Devkit                   | Module          | Flash voltage |
++==========================+=================+===============+
+| PICO Kit                 | PICO-D4         | 3.3V          |
++--------------------------+-----------------+ (see steps    +
+| DevKitC                  | Wroom-32 Series | below)        |
++--------------------------+                 +               +
+| WroverKit v2 and earlier |                 |               |
++--------------------------+-----------------+---------------+
+| WroverKit v3             | Wrover          | 1.8V          |
++--------------------------+-----------------+---------------+
+
+If your board requires internal regulator with 3.3v output, to make it
+compatible with SD pullup, you can either:
+
+  - **In the case using ESP32 host only**, external pullup can be omitted and an
+    internal pullup can be enabled using a ``gpio_pullup_en(GPIO_NUM_12);`` call.
+    Most SD cards work fine when an internal pullup on GPIO12 line is enabled.
+    Note that if ESP32 experiences a power-on reset while the SD card is
+    sending data, high level on GPIO12 can be latched into the bootstrapping
+    register, and ESP32 will enter a boot loop until external reset with
+    correct GPIO12 level is applied.
+  - **In the case using ESP32 slave in 1-bit mode**, speicfy
+    ``SDIO_SLAVE_FLAG_DAT2_DISABLED`` in the slave to avoid slave detecting on
+    DAT2 line. Note the host will not know 4-bit mode is not supported any more
+    by the standard CCCR register. You have to tell the host use 1-bit only.
+  - **For ESP32 host or slave**, another option is to burn the flash voltage
+    selection efuses. This will permanently select 3.3V output voltage for the
+    internal regulator, and GPIO12 will not be used as a bootstrapping pin.
+    Then it is safe to connect a pullup resistor to GPIO12. This option is
+    suggested for production use. NOTE this cannot be reverted once the EFUSE
+    is burnt.
+
+      The following command can be used to program flash voltage selection efuses **to 3.3V**:
+
+          components/esptool_py/esptool/espefuse.py set_flash_voltage 3.3V
+
+      This command will burn the `XPD_SDIO_TIEH`, `XPD_SDIO_FORCE`, and
+      `XPD_SDIO_REG` efuses. With all three burned to value 1, the internal
+      VDD_SDIO flash voltage regulator is permanently enabled at 3.3V. See
+      the technical reference manual for more details.
+
+      `espefuse.py` has a `--do-not-confirm` option if running from an automated flashing script.
+
+GPIO2 Strapping pin
+-------------------
+
+GPIO2 pin is used as a bootstrapping pin, and should be low to enter UART
+download mode. You may find it unable to enter the UART download mode if you
+correctly connect the pullup of SD on GPIO2. For WroverKit v3, there are
+dedicated circuits to pulldown the GPIO2 when downloading. For other boards,
+one way to do this is to connect GPIO0 and GPIO2 using a jumper, and then the
+auto-reset circuit on most development boards will pull GPIO2 low along with
+GPIO0, when entering download mode.
+
+- Some boards have pulldown and/or LED on GPIO2. LED is usually ok, but
+  pulldown will interfere with D0 signals and must be removed. Check the
+  schematic of your development board for anything connected to GPIO2.

docs/en/api-reference/peripherals/sdio_slave.rst

@@ -4,9 +4,6 @@ SDIO Card Slave Driver
 Overview
 --------
 
-.. note:: At the moment, this code has been proven to work on the Wrover-Kit V3. Earlier versions of the Wrover-Kit
-    and other development kits are electrically incompatible with this code. Functionality on other devboards is untested.
-
 The ESP32 SDIO Card peripherals (Host, Slave) shares two sets of pins as below table.
 The first set is usually occupied by SPI0 bus which is responsible for the SPI flash holding the code to run.
 This means SDIO slave driver can only runs on the second set of pins while SDIO host is not using it.
@@ -29,15 +26,33 @@ This means SDIO slave driver can only runs on the second set of pins while SDIO
 | DAT3     | 10    | 13    |
 +----------+-------+-------+
 
-The SDIO slave can run under 3 modes: SPI, 1-bit SD and 4-bit SD modes, which is detected automatically by the
+The SDIO slave can run under 3 modes: SPI, 1-bit SD and 4-bit SD modes, which
-hardware. According to the SDIO specification, the host initialize the slave into SD mode by first sending CMD0 with
+is detected automatically by the hardware. According to the SDIO
-DAT3 pin high, while initialize the slave into SPI mode by sending CMD0 with CS pin (the same pin as DAT3) low. After the
+specification, CMD and DAT0-3 lines should be pulled up no matter in 1-bit,
-initialization, the host can enable the 4-bit SD mode by writing CCCR register 0x07 by CMD52. All the bus detection
+4-bit or SPI mode. Then the host initialize the slave into SD mode by first
-process are handled by the slave peripheral.
+sending CMD0 with DAT3 pin high, while initialize the slave into SPI mode by
+sending CMD0 with CS pin (the same pin as DAT3) low.
 
-The host has to communicate with the slave by an ESP-slave-specific protocol. The slave driver offers 3 services over
+.. note:: CMD and DATA lines D0-D3 of the card should be pulled up by 50KOhm resistor
-Function 1 access by CMD52 and CMD53: (1) a sending FIFO and a receiving FIFO, (2) 52 8-bit R/W registers shared by
+  even in 1-bit mode or SPI mode. Most official devkits don't meet the pullup
-host and slave, (3) 16 interrupt sources (8 from host to slave, and 8 from slave to host).
+  requirements by default, and there are conflicts on strapping pins as well.
+  Please refer to :doc:`sd_pullup_requirements` to see how to setup your
+  system correctly.
+
+.. toctree::
+    :hidden:
+
+    sd_pullup_requirements
+
+After the initialization, the host can enable the 4-bit SD mode by writing
+CCCR register 0x07 by CMD52. All the bus detection process are handled by the
+slave peripheral.
+
+The host has to communicate with the slave by an ESP-slave-specific protocol.
+The slave driver offers 3 services over Function 1 access by CMD52 and CMD53:
+(1) a sending FIFO and a receiving FIFO, (2) 52 8-bit R/W registers shared by
+host and slave, (3) 16 interrupt sources (8 from host to slave, and 8 from
+slave to host).
 
 Terminology
 ^^^^^^^^^^^
@@ -215,6 +230,7 @@ There are several ways to use the ``arg`` in the queue parameter:
 
        More about this, see :example:`peripherals/sdio`.
 
+
 Application Example
 -------------------
 

docs/en/api-reference/peripherals/sdmmc_host.rst

@@ -60,6 +60,8 @@ See :doc:`SD/SDIO/MMC Driver <../storage/sdmmc>` for the higher level driver whi
 
 See :doc:`SD SPI Host Driver <sdspi_host>` for a similar driver which uses SPI controller and is limited to SPI mode of SD protocol.
 
+See :doc:`sd_pullup_requirements` for pullup support and compatiblities about modules and devkits.
+
 API Reference
 -------------
 

docs/zh_CN/api-reference/peripherals/sd_pullup_requirements.rst

@@ -0,0 +1 @@
+.. include:: ../../../en/api-reference/peripherals/sd_pullup_requirements.rst