IDF claims IO20 is invalid, but ESP-PICO-V3 exposes IO20 (IDFGH-4154)

[corecode]

Environment

• Development Kit: none
• Module or chip used: [ESP32-PICO-V3]
• IDF version (run git describe --tags to find it):
  // v4.1-352-g5d258af93
• Build System: CMake
• Compiler version (run xtensa-esp32-elf-gcc --version to find it):
  // xtensa-esp32-elf-gcc (crosstool-NG esp-2020r3) 8.4.0
• Operating System: Linux
• Using an IDE?: No
• Power Supply: external 5V

Problem Description

ledc_channel_config does not accept IO20 and reports

ledc: ledc_channel_config(380): gpio_num argument is invalid

Expected Behavior

IO20 can be used

Actual Behavior

IO20 cannot be used

Steps to reproduce

1. call ledc_channel_config with gpio_num = 20

Fix

diff --git a/components/soc/esp32/gpio_periph.c b/components/soc/esp32/gpio_periph.c
index d8a30b0af..0a6eee285 100644
--- a/components/soc/esp32/gpio_periph.c
+++ b/components/soc/esp32/gpio_periph.c
@@ -35,7 +35,7 @@ const uint32_t GPIO_PIN_MUX_REG[GPIO_PIN_COUNT] = {
     IO_MUX_GPIO17_REG,
     IO_MUX_GPIO18_REG,
     IO_MUX_GPIO19_REG,
-    0,
+    IO_MUX_GPIO20_REG,
     IO_MUX_GPIO21_REG,
     IO_MUX_GPIO22_REG,
     IO_MUX_GPIO23_REG,

[ginkgm]

Hello @corecode ,
according to the datasheet (section A.4), there is no such GPIO20 on the chip. So it's not available.

The dev board may be desinged in this way to support more modules, but for ESP32, the pin is not available even if you remove the restriction.

[boarchuz]

@ginkgm
PICO-V3 datasheet notes:
Comparing to other ESP32 series chips, ESP32-PICO-V3 has an additional pin GPIO20

[alessandro-montanari]

I'm using the pico v3 and having the same problem. Using the same fix suggested by @corecode I can use the pin 20 just fine.

See also #387