Feature request: Pass arbitrary data pointer in HAL callbacks

[tdecker2]

It is really sad that ST decided to not implement this requested and really helpful feature: https://github.com/STMicroelectronics/STM32CubeG4/issues/23

Maybe we can change their minds by creating some more attention to this topic here? Leave a comment, when you also find this useful

Example solution for the I²C driver by adding a void* to the handle:

typedef struct __I2C_HandleTypeDef
{
/* Rest of struct... */
#if (USE_HAL_CALLBACK_CONTEXT == 1)
  void *UserContext;
#endif /* USE_HAL_CALLBACK_CONTEXT */
} I2C_HandleTypeDef;

[LCE]

I find it useful.

But for all the important stuff - and when memory size is small - I'm using direct register access and no HAL.

Or I edit the HAL driver as I need them, as I don't let anything update these anyway.

[Pavel A.]

The context can be implemented in the "idiomatic Linux way": make the xxx_HandleTypeDef struct part of a bigger user defined struct, then use offsettof to access the outer struct with all your custom fields. In C++ way, "subclass" the xxx_HandleTypeDef structs.

IMHO ST cannot just add the user context pointer, because the other half of users that don't need it would object (waste of precious memory and CPU cycles...)

[Andrew Neil]

---

@Pavel A. wrote:

IMHO ST cannot just add the user context pointer, because the other half of users that don't need it would object (waste of precious memory and CPU cycles...)

---

As shown in the OP, it's optional:

typedef struct __I2C_HandleTypeDef
{
/* Rest of struct... */
#if (USE_HAL_CALLBACK_CONTEXT == 1)
  void *UserContext;
#endif /* USE_HAL_CALLBACK_CONTEXT */
} I2C_HandleTypeDef;

 So it would make no difference at all to those users who didn't want it.

[SofLit]

Hello @tdecker2 ,

Thank you for your suggestion. 

Just one question: why this needs to be in the activated "registered callback" context? couldn't be also used in the "weak" callbacks?

[Tesla DeLorean]

Couldn't you just overload the structure with whatever you want? Put a structure in front or behind the one ST provides for? They just blindly pass a pointer, you can concatenate what ever you want with it.