This issue is reported from https://github.com/espressif/esp-idf/issues/304.
We found that when we operate the hw command registers in I2C struct, sometimes the behaviour would be different in DEBUG/RELEASE optimisation level:
The code looks like this:
I2C[i2c_num]->command[p_i2c->cmd_idx].byte_num -= 0;
In DEBUG configuration:
I2C[i2c_num]->command[p_i2c->cmd_idx].byte_num -= 0;
400f3ab0: 3388 l32i.n a8, a3, 12
400f3ab2: 14c882 addi a8, a8, 20
400f3ab5: a08840 addx4 a8, a8, a4
400f3ab8: 0020c0 memw
400f3abb: 2898 l32i.n a9, a8, 8
400f3abd: 0020c0 memw
400f3ac0: 28b8 l32i.n a11, a8, 8
400f3ac2: 74a090 extui a10, a9, 0, 8
400f3ac5: 00af92 movi a9, 0xffffff00
400f3ac8: 109b90 and a9, a11, a9
400f3acb: 2099a0 or a9, a9, a10
400f3ace: 0020c0 memw
400f3ad1: 2899 s32i.n a9, a8, 8
In RELEASE configuration:
I2C[i2c_num]->command[p_i2c->cmd_idx].byte_num -= 0;
400f2ba2: 580572 l8ui a7, a5, 88
400f2ba5: 747070 extui a7, a7, 0, 8
400f2ba8: 0020c0 memw
400f2bab: 584572 s8i a7, a5, 88
Looks like the compiler will make it a 8bit operation after optimisation.
But the register value changes from 0x901 to 0x101.
After this 8-bit optimisation, the 11th bit changed from 1 to zero, which caused this error.
We are still trying to find out why that happens, because there might be some risk when operating the register struct.
This is a workaround to avoid "-=" operation on I2C register struct fields.
2. update example comments and other minor changes
3. rename API: i2c_cmd_link_create/i2c_cmd_link_delete (+4 squashed commits)
Squashed commits:
[2e0ac3e] 1. coding style: add one space after condition key words.
2. modify i2c.h, use gpio_num_t instead of int, improve comments of return values
3. add i2c index in index.rst
4. add readme for i2c example
[4991d92] update i2c.doc
[88b672e] driver: i2c
1. add mux and spin lock to run in a thread-safe way.
2. modify example code
[4eb15fe] driver: i2c code
1. add i2c master code
2. add i2c slave code
3. add i2c example code
4. add DRAM_ATTR for I2C array
