Donny9 opened a new pull request, #17746:
URL: https://github.com/apache/nuttx/pull/17746
## Summary
This commit adds a new lower-half driver implementation for I2C bit-bang
that uses IO expander pins as the GPIO backend, enabling I2C bit-bang
functionality on systems where direct GPIO access is not available or when I2C
needs to be implemented using IO expander pins.
Background:
The existing I2C bit-bang driver (i2c_bitbang.c) provides a generic
upper-half implementation that requires a platform-specific lower-half to
control the SDA and SCL GPIO lines. Previously, each platform had to implement
its own lower-half using direct GPIO access.
Usage Example:
```c
FAR struct ioexpander_dev_s *ioe = /* get IO expander */; FAR struct
i2c_master_s *i2c;
/* Initialize I2C bit-bang using IO expander pins 10 (SCL) and 11 (SDA) */
i2c = i2c_bitbang_ioexpander_initialize(ioe, 10, 11, 0); if (i2c)
{
/* Use i2c master device normally */
}
```
## Impact
This commit introduces a reusable lower-half implementation that:
- Uses the standard IO expander API (IOEXP_WRITEPIN, IOEXP_READPIN)
- Configures pins as open-drain outputs for proper I2C operation
- Provides a simple initialization function that takes:
* Pointer to IO expander device
* SCL pin number
* SDA pin number
* I2C bus number
## Testing
test for tc4d9 evb,
<img width="1040" height="122" alt="image"
src="https://github.com/user-attachments/assets/4792f8e4-bcda-48ae-9078-9c612611177f";
/>
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