new I2C driver sccb-ng.c is mistakenly byte-swapping `reg` in `SCCB_Write16()` and `SCCB_Write_Addr16_Val16()`

[dhalbert]

Checklist

• Checked the issue tracker for similar issues to ensure this is not a duplicate
• Read the documentation to confirm the issue is not addressed there and your configuration is set correctly
• Tested with the latest version to ensure the issue hasn't been fixed

How often does this bug occurs?

always

Expected behavior

SCCB_Write16() and SCCB_Write_Addr16_Val16() should send the reg address in the correct order to the I2C-connected camera. Instead, the address is byte-swapped.

SCCB_Read16() and SCCB_Read_Addr16_Val16() are fine, and the 8-bit routines are also fine.

Actual behavior (suspected bug)

SCCB_Write16() and SCCB_Write_Addr16_Val16() byte-swap the reg address value twice, instead of just once. Here is the code in SCCB_Read16(), which works:

    uint16_t reg_htons = LITTLETOBIG(reg);
    uint8_t *reg_u8 = (uint8_t *)&reg_htons;

    esp_err_t ret = i2c_master_transmit_receive(dev_handle, reg_u8, 2, rx_buffer, 1, TIMEOUT_MS);

Suppose reg is 0x0102. Then reg_htons will be 0x0201. reg_u8[0] will be 0x01, and reg_u8[1] will be 0x02.

But in SCCB_Write16(), the code is:

    uint16_t reg_htons = LITTLETOBIG(reg);

    uint8_t tx_buffer[3];
    tx_buffer[0] = reg_htons >> 8;
    tx_buffer[1] = reg_htons & 0x00ff;
    tx_buffer[2] = data;

    esp_err_t ret = i2c_master_transmit(dev_handle, tx_buffer, 3, TIMEOUT_MS);

As before, suppose reg is 0x0102. Then reg_htons will be 0x0201. But then tx_buffer[0] will be 0x02, because it is set to reg_htons >> 8. And tx_buffer[1] will be 0x01. This is swapped from what it should be.

Error logs or terminal output

No response

Steps to reproduce the behavior

This occurs whenever a 16-bit register is written. I was converting CircuitPython code to use the new driver_esp_i2c, and updated our code to use the new code in esp32-camera. The camera did not work. I did some read/write/read logging to verify the registers were being written correctly, and they were not.

Project release version

latest master as of 2024-09-27

System architecture

Intel/AMD 64-bit (modern PC, older Mac)

Operating system

Linux

Operating system version

Ubuntu 24.04

Shell

Bash

Additional context

#677, the PR for updating to the new I2C driver, was only tested with an OV2640.

(Thank you @playduck, for the PR! We were blocked without it.)

There is this comment in the PR:

I've translated the functions SCCB_Read16, SCCB_Write16, SCCB_Read_Addr16_Val16 and SCCB_Write_Addr16_Val16 as well. However it seems like these are entirely unused [not true].

So these routines were not tested. But there are uses of these routines for various cameras in sensors/. We use the OV5640, and it needs 16-bit register writes.

I think I can come up with a PR.