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doc(sdio_slave): add descriptions about conflicts on MTDI pin
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michael
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docs/en/api-reference/peripherals/sd_pullup_requirements.rst
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153
docs/en/api-reference/peripherals/sd_pullup_requirements.rst
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SD Pullup Requirements
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======================
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CMD and DATA lines D0-D3 of the slave should be pulled up by 50KOhm resistor
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even in 1-bit mode or SPI mode. The pullups of the slave cards should be
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connected even if they're not connected to the host.
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The MTDI strapping pin is incompatible with DAT2 line pull-up by default
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when the code flash is 3.3V. See :ref:`mtdi_strapping_pin` below.
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Pullup inside Official Modules
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------------------------------
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For Espressif official modules, different weak pullups / pulldowns are
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connected to CMD, and DATA pins as below. To use these modules,
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these pins are required to be pulled up by 50KOhm resistors, since internal
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weak pullups are insufficient.
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+-----------------------+-----+--------------------------+------+----------------------+------+
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| GPIO | 15 | 2 | 4 | 12 | 13 |
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+=======================+=====+==========================+======+======================+======+
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| Name | CMD | DAT0 | DAT1 | DAT2 | DAT3 |
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+-----------------------+-----+--------------------------+------+----------------------+------+
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| At startup | WPU | WPD | WPD | PU for 1.8v flash; | WPU |
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| | | | | WPD for 3.3v flash | |
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+-----------------------+-----+--------------------------+------+----------------------+------+
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| Strapping requirement | | Low to download to flash | | High for 1.8v flash; | |
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| | | | | Low for 3.3v flash | |
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+-----------------------+-----+--------------------------+------+----------------------+------+
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- WPU: Weak pullup
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- WPD: Weak pulldown
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- PU: Pullup inside the module
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For Wrover modules, they use 1.8v flash, and have pullup on GPIO12 inside.
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For Wroom-32 Series, PICO-D4 modules, they use 3.3v flash, and is weakly
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pulled down internally. See :ref:`mtdi_strapping_pin` below.
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Pullup on Official Devkit (WroverKit)
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--------------------------------------
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For official Wrover Kit (till version 3), some of the pullups are provided on
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the board as the table below. For other devkits that don't have pullups,
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please connect them yourselves.
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+-----------------------+-----+------+------+------+---------+
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| GPIO | 15 | 2 | 4 | 12 | 13 |
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+=======================+=====+======+======+======+=========+
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| Name | CMD | DAT0 | DAT1 | DAT2 | DAT3 |
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+-----------------------+-----+------+------+------+---------+
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| Pullup on the Kit | PU | PU | PU | | PU & PD |
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+-----------------------+-----+------+------+------+---------+
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- PU: Pullup
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- PD: Pulldown
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The DAT3 pullup conflicts with JTAG pulldown in WroverKit v3 and earlier, please
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either:
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1. pull it up by resistor less than 5KOhm (2kOhm suggested) in 4-bit mode.
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2. pull it up or drive it high by host or VDD3.3V in 1-bit mode.
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.. _mtdi_strapping_pin:
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MTDI strapping pin
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------------------
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MTDI (GPIO12) is used as a bootstrapping pin to select output voltage of an
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internal regulator which powers the flash chip (VDD_SDIO). This pin has an
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internal pulldown so if left unconnected it will read low at reset (selecting
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default 3.3V operation). When adding a pullup to this pin for SD card
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operation, consider the following:
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- For boards which don't use the internal regulator (VDD_SDIO) to power the
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flash, GPIO12 can be pulled high.
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- For boards which use 1.8V flash chip, GPIO12 needs to be pulled high at
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reset. This is fully compatible with SD card operation.
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- On boards which use the internal regulator and a 3.3V flash chip, GPIO12
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must be low at reset. This is incompatible with SD card operation. Please
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check the table below to see whether your modules/kits use 3.3v flash.
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+-----------------+---------------+--------------------------------------+
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| Module | Flash voltage | DAT2 connections |
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+=================+===============+======================================+
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| PICO-D4 | 3.3V | Internal PD, change EFUSE and pullup |
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+-----------------+ + or disable DAT2 line* +
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| Wroom-32 Series | | |
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+-----------------+---------------+--------------------------------------+
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| Wrover | 1.8V | Internal PU, pullup suggested |
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+-----------------+---------------+--------------------------------------+
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Official devkits of different types and version mount different types of
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modules, please refer to the table below to see whether your devkit can
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support SDIO slave without steps above.
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+--------------------------+-----------------+---------------+
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| Devkit | Module | Flash voltage |
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+==========================+=================+===============+
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| PICO Kit | PICO-D4 | 3.3V |
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+--------------------------+-----------------+ (see steps +
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| DevKitC | Wroom-32 Series | below) |
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+--------------------------+ + +
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| WroverKit v2 and earlier | | |
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+--------------------------+-----------------+---------------+
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| WroverKit v3 | Wrover | 1.8V |
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+--------------------------+-----------------+---------------+
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If your board requires internal regulator with 3.3v output, to make it
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compatible with SD pullup, you can either:
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- **In the case using ESP32 host only**, external pullup can be omitted and an
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internal pullup can be enabled using a ``gpio_pullup_en(GPIO_NUM_12);`` call.
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Most SD cards work fine when an internal pullup on GPIO12 line is enabled.
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Note that if ESP32 experiences a power-on reset while the SD card is
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sending data, high level on GPIO12 can be latched into the bootstrapping
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register, and ESP32 will enter a boot loop until external reset with
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correct GPIO12 level is applied.
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- **In the case using ESP32 slave in 1-bit mode**, speicfy
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``SDIO_SLAVE_FLAG_DAT2_DISABLED`` in the slave to avoid slave detecting on
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DAT2 line. Note the host will not know 4-bit mode is not supported any more
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by the standard CCCR register. You have to tell the host use 1-bit only.
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- **For ESP32 host or slave**, another option is to burn the flash voltage
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selection efuses. This will permanently select 3.3V output voltage for the
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internal regulator, and GPIO12 will not be used as a bootstrapping pin.
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Then it is safe to connect a pullup resistor to GPIO12. This option is
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suggested for production use. NOTE this cannot be reverted once the EFUSE
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is burnt.
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The following command can be used to program flash voltage selection efuses **to 3.3V**:
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components/esptool_py/esptool/espefuse.py set_flash_voltage 3.3V
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This command will burn the `XPD_SDIO_TIEH`, `XPD_SDIO_FORCE`, and
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`XPD_SDIO_REG` efuses. With all three burned to value 1, the internal
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VDD_SDIO flash voltage regulator is permanently enabled at 3.3V. See
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the technical reference manual for more details.
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`espefuse.py` has a `--do-not-confirm` option if running from an automated flashing script.
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GPIO2 Strapping pin
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-------------------
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GPIO2 pin is used as a bootstrapping pin, and should be low to enter UART
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download mode. You may find it unable to enter the UART download mode if you
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correctly connect the pullup of SD on GPIO2. For WroverKit v3, there are
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dedicated circuits to pulldown the GPIO2 when downloading. For other boards,
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one way to do this is to connect GPIO0 and GPIO2 using a jumper, and then the
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auto-reset circuit on most development boards will pull GPIO2 low along with
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GPIO0, when entering download mode.
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- Some boards have pulldown and/or LED on GPIO2. LED is usually ok, but
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pulldown will interfere with D0 signals and must be removed. Check the
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schematic of your development board for anything connected to GPIO2.
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@ -4,9 +4,6 @@ SDIO Card Slave Driver
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Overview
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--------
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.. note:: At the moment, this code has been proven to work on the Wrover-Kit V3. Earlier versions of the Wrover-Kit
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and other development kits are electrically incompatible with this code. Functionality on other devboards is untested.
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The ESP32 SDIO Card peripherals (Host, Slave) shares two sets of pins as below table.
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The first set is usually occupied by SPI0 bus which is responsible for the SPI flash holding the code to run.
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This means SDIO slave driver can only runs on the second set of pins while SDIO host is not using it.
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@ -29,15 +26,33 @@ This means SDIO slave driver can only runs on the second set of pins while SDIO
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| DAT3 | 10 | 13 |
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+----------+-------+-------+
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The SDIO slave can run under 3 modes: SPI, 1-bit SD and 4-bit SD modes, which is detected automatically by the
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hardware. According to the SDIO specification, the host initialize the slave into SD mode by first sending CMD0 with
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DAT3 pin high, while initialize the slave into SPI mode by sending CMD0 with CS pin (the same pin as DAT3) low. After the
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initialization, the host can enable the 4-bit SD mode by writing CCCR register 0x07 by CMD52. All the bus detection
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process are handled by the slave peripheral.
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The SDIO slave can run under 3 modes: SPI, 1-bit SD and 4-bit SD modes, which
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is detected automatically by the hardware. According to the SDIO
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specification, CMD and DAT0-3 lines should be pulled up no matter in 1-bit,
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4-bit or SPI mode. Then the host initialize the slave into SD mode by first
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sending CMD0 with DAT3 pin high, while initialize the slave into SPI mode by
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sending CMD0 with CS pin (the same pin as DAT3) low.
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The host has to communicate with the slave by an ESP-slave-specific protocol. The slave driver offers 3 services over
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Function 1 access by CMD52 and CMD53: (1) a sending FIFO and a receiving FIFO, (2) 52 8-bit R/W registers shared by
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host and slave, (3) 16 interrupt sources (8 from host to slave, and 8 from slave to host).
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.. note:: CMD and DATA lines D0-D3 of the card should be pulled up by 50KOhm resistor
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even in 1-bit mode or SPI mode. Most official devkits don't meet the pullup
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requirements by default, and there are conflicts on strapping pins as well.
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Please refer to :doc:`sd_pullup_requirements` to see how to setup your
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system correctly.
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.. toctree::
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:hidden:
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sd_pullup_requirements
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After the initialization, the host can enable the 4-bit SD mode by writing
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CCCR register 0x07 by CMD52. All the bus detection process are handled by the
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slave peripheral.
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The host has to communicate with the slave by an ESP-slave-specific protocol.
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The slave driver offers 3 services over Function 1 access by CMD52 and CMD53:
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(1) a sending FIFO and a receiving FIFO, (2) 52 8-bit R/W registers shared by
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host and slave, (3) 16 interrupt sources (8 from host to slave, and 8 from
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slave to host).
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Terminology
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^^^^^^^^^^^
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@ -215,6 +230,7 @@ There are several ways to use the ``arg`` in the queue parameter:
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More about this, see :example:`peripherals/sdio`.
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Application Example
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-------------------
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@ -60,6 +60,8 @@ See :doc:`SD/SDIO/MMC Driver <../storage/sdmmc>` for the higher level driver whi
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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.
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See :doc:`sd_pullup_requirements` for pullup support and compatiblities about modules and devkits.
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API Reference
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-------------
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@ -0,0 +1 @@
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.. include:: ../../../en/api-reference/peripherals/sd_pullup_requirements.rst
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