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sdmmc: fix explanation of flash voltage regulator configuration efuses

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- low level on GPIO12 corresponds to 3.3V output, not 1.8V
- add espefuse.py commands to burn efuses
- add XPD_SDIO_REG to the list of efuses which must be set

Reported on the forum: http://esp32.com/viewtopic.php?f=2&t=849&start=10#p4170
This commit is contained in:
Ivan Grokhotkov 2017-01-16 01:19:14 +08:00 committed by Ivan Grokhotkov
parent e5feeb195f
commit a2ace698ed
1 changed files with 13 additions and 2 deletions
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15
examples/27_sd_card/README.md
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@ -40,9 +40,20 @@ GPIO12 is used as a bootstrapping pin to select output voltage of an internal re
- For boards which don't use the internal regulator, GPIO12 can be pulled high.
- On boards which use the internal regulator and a 3.3V flash chip, GPIO12 should be pulled up high, which is compatible with SD card operation.
- For boards which use 1.8V flash chip, GPIO12 needs to be low at reset.
- For boards which use 3.3V flash chip, GPIO12 needs to be low at reset.
* In this case, 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.
* Another option is to program flash voltage selection efuses: set `SDIO_TIEH=0` and `SDIO_FORCE=1`. This will permanently select 1.8v output voltage for the internal regulator, and GPIO12 will not be used as a bootstrapping pin anymore. Then it is safe to connect a pullup resistor to GPIO12. This option is suggested for production use.
* Another option is to program flash voltage selection efuses: set `XPD_SDIO_TIEH=1`, `XPD_SDIO_FORCE=1`, and `XPD_SDIO_REG = 1`. This will permanently select 3.3V output voltage for the internal regulator, and GPIO12 will not be used as a bootstrapping pin anymore. Then it is safe to connect a pullup resistor to GPIO12. This option is suggested for production use.
The following commands can be used to program flash voltage selection efuses **to 3.3V**:
```sh
# Override flash regulator configuration using efuses
components/esptool_py/esptool/espefuse.py burn_efuse XPD_SDIO_FORCE
# Select 3.3V output voltage
components/esptool_py/esptool/espefuse.py burn_efuse XPD_SDIO_TIEH
# Enable internal voltage regulator
components/esptool_py/esptool/espefuse.py burn_efuse XPD_SDIO_REG
```
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