mirror of
https://github.com/espressif/esp-idf.git
synced 2024-10-05 20:47:46 -04:00
94b91ee4af
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.