116 lines
5.2 KiB
Markdown
116 lines
5.2 KiB
Markdown
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### SDIO Example
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## Introduction
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These two projects illustrate the SDIO driver (host and slave). The host
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example shows how to initialize a SDIO card, respond to a slave interrupt, as
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well as reading and writing registers and buffers. The slave is a dedicated
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peripheral, providing 8 interrupts, 52 8-bit R/W registers, an input FIFO and
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an output FIFO. The example shows how to configure the driver and use these
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feature.
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The host first tell the slave to write the registers to a specified value,
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then reads and prints the value from the slave. Then tell the slave to send 8
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interrupts to the host. Then the host start sending data to the slave FIFO
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and then reads from the slave FIFO in loops.
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## Wiring
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The SDIO protocol requires at least 4 lines (one more line than SD memory
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protocol): CMD, CLK, DAT0 and DAT1. DAT1 is mandatory for the interrupt. DAT2
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is required if 4-bit mode is used. DAT3 is required in 4-bit mode (connected
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to host), or required by the slave as mode detect in 1-bit mode (pull up). It
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is okay in 1-bit mode to leave DAT3 of host disconnected.
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Please run wires between the slave and master to make the example function
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(pins are the same for the host and the slave):
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======== =========
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Signal GPIO NUM
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======== =========
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CLK GPIO14
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CMD GPIO15
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DAT0 GPIO2
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DAT1 GPIO4
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DAT2 GPIO12
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DAT3 GPIO13
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Ground GND
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======== =========
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CMD and DAT0-3 lines require to be pulled up by 50KOhm resistors even in
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1-bit mode. See *Board Compability* below for details. In 1-bit mode, the
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host can make use of DAT2 and DAT3, however the slave should leave them alone
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but pulled up.
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Be aware that the example uses lines normally reserved for JTAG. If you're
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using a board with JTAG functions, please remember to remove jumpers
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connecting to the JTAG adapter. The SD peripheral works at a high frequency
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and uses native pins, there's no way to configure it to other pins through
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the GPIO matrix.
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Please make sure CMD and DATA lines are pulled up by 50KOhm resistors even in
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1-bit mode or SPI mode, which is required by the SD specification.
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The 4-bit mode can be configured in the menuconfig. If the 4-bit mode is not
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used, the host will not control the DAT3 line, the slave hardware is
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responsible to pull-up the line (or the slave may run into the SPI mode and
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cause a crash).
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The host uses HS mode by default. If the example does not work properly,
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please try connecting two boards by short wires, grounding between two boards
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better or disabling the HS mode in menuconfig.
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## Board compatibility
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1. If you're using a board (e.g. WroverKit v2 and before, PICO, DevKitC)
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which is not able to drive GPIO2 low on downloading, please remember to
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disconnect GPIO2 between two boards when downloading the application.
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2. It is suggested to use the official Wrover Kit as the slave. This is
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because Wrover Kits have pullups on CMD, DAT0 and DAT1. Otherwise you'll have
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to connect the pullups manually (or use the Wrover Kit as the host). However,
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due to a PCB issue, Wrover Kits v3 and earlier have pullup v.s. pulldown
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conflicts on DAT3 line. You'll have to:
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1. Pull up GPIO13 by resistor of 5KOhm or smaller (2KOhm suggested)
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in 4-bit mode.
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2. Pull up, or tie GPIO13 to VDD3.3 in 1-bit mode.
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To help you faster evaluate the SDIO example on devkits without pullups,
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you can uncomment the pullup enable flags in the initialization code of
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the app_main of host or slave. This enables internal weak pullups on CMD,
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DAT0 and DAT1 and DAT3 lines. However please don't rely on internal weak
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pullups in your own design.
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3. Moreover, if your slave devkit is using code flash of 3.3V, it is required
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to pull down DAT2 line to set proper flash voltage. This conflicts with SDIO
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pullup requirements. Currently devkits using PICO-D4 and Wroom-32 series
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modules have this problem. You can either:
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- Use Wrover Kit v3 which integrates a Wrover module
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- Still use PICO-D4 or Wroom-32 Series modules as the slave, however:
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- Don't connect the DAT2 pin and leave it floating. This means
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you have to use 1-bit mode in the host. ``SDIO_DAT2_DISABLED``
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option should be enabled in the menuconfig to avoid using of
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DAT2. Or:
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- Burn the EFUSE to force the module using 3.3V as the flash
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voltage. In this way the voltage of flash doesn't depend on MTDI
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any more, connect DAT2 to the host and make sure it is pulled up
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correctly. See document below.
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See docs in the programming guide ``api_reference/peripherals/sdio_slave``
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and ``api_reference/peripherals/sd_pullup_requirements`` to see more
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descriptions about pullups and MTDI requirements and solutions of official
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modules and devkits.
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## About esp_slave component in this example
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The component in this example shows how to communicate with esp32 sdio slave
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correctly. However, currently it is for example purpose only.
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The example shows how to talk with the slave, but doesn't show how to handle
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exceptions. Assertion fails if any of the preconditions (connections,
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grounding, slave data preparation, etc.) is not met.
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Please do check and handle the return value in your real product.
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