I had some problems understanding how assembler commands work for ULP on ESP32
This is an example for I_WR_REG
In the documentation we have I_WR_REG(reg, low_bit, high_bit, val)
We have this table for the bits RTC_GPIO and GPIO
| Bit | RTC | GPIO |
|---|---|---|
| bit 14 | RTC_GPIO 0 | GPIO 36 |
| bit 15 | RTC_GPIO 1 | GPIO 37 |
| bit 16 | RTC_GPIO 2 | GPIO 38 |
| bit 17 | RTC_GPIO 3 | GPIO 39 |
| bit 18 | RTC_GPIO 4 | GPIO 34 |
| bit 19 | RTC_GPIO 5 | GPIO 35 |
| bit 20 | RTC_GPIO 6 | GPIO 25 |
| bit 21 | RTC_GPIO 7 | GPIO 26 |
| bit 22 | RTC_GPIO 8 | GPIO 33 |
| bit 23 | RTC_GPIO 9 | GPIO 32 |
| bit 24 | RTC_GPIO 10 | GPIO 4 |
| bit 25 | RTC_GPIO 11 | GPIO 0 |
| bit 26 | RTC_GPIO 12 | GPIO 2 |
| bit 27 | RTC_GPIO 13 | GPIO 15 |
| bit 28 | RTC_GPIO 14 | GPIO 13 |
| bit 29 | RTC_GPIO 15 | GPIO 12 |
| bit 30 | RTC_GPIO 16 | GPIO 14 |
| bit 31 | RTC_GPIO 17 | GPIO 27 |
So suppose you want to turn on a led GPIO 02 (that is the led included on the board)
I_WR_REG(RTC_GPIO_OUT_REG, 26, 26, 1)
That will do it
Now you will find some examples with:
I_WR_REG(RTC_GPIO_OUT_REG, 26, 27, 1)
1 in binary is 01
bit 26 is GPIO02 ----> 1
bit 27 is GPIO15 ----> 0
GPIO02 will have 1
GPIO15 will have 0
I_WR_REG(RTC_GPIO_OUT_REG, 26, 27, 2)
GPIO02 will have 0, GPIO15 will have 1
I_WR_REG(RTC_GPIO_OUT_REG, 26, 27, 3)
GPIO02 will have 1, GPIO15 will have 1
I_WR_REG(RTC_GPIO_OUT_REG, 22, 26, 21)
21 in binary is 10111
bit 22 is GPIO33 --> 1
bit 23 is GPIO32 --> 0
bit 24 is GPIO04 --> 1
bit 25 is GPIO00 --> 1
bit 26 is GPIO02 --> 1
Now what is the problem.
We need to check if the GPIO is input/output or it will not work. Example RTC_GPIO0 (GPIO36) is INPUT ONLY
https://www.espressif.com/sites/default/files/1a-esp32_pin_list_en-v0.1.pdf