cpu/stm32/periph/i2c: export PERIPH_I2C_MAX_BYTES_PER_FRAME

[fabian18]

Contribution description

This exports the previously internally defined MAX_BYTES_PER_FRAME in cpu/stm32/periph/i2c_1.c.
If such a limit exists, a driver must know about it.

Testing procedure

CI

Issues/PRs references

The problem came up in #19270.

[fabian18]

Maybe someone remembers why this is not the case for i2c_2.c?

[benpicco]

It uses length when generating the start condition

start(i2c, (addr << 1) | (length << I2C_CR2_NBYTES_Pos) | cr2_flags, flags);

so this must be some sort of hardware limitation.

[fabian18]

I have seen this too but I2C_CR2_NBYTES_Msk is defined by (almost) every stm32 so I don´t know why this limit exists for only a few of them

[fabian18]

Maybe @aabadie knows why this limit exists?

[HendrikVE]

Why not putting it to the corresponding periph_cpu.h files? BTW I'm wondering: Is BYTES_PER_FRAME really the correct wording for this in I2C terminology?

[riot-ci]

Murdock results

✔️ PASSED

26363e9 cpu/stm32/periph/i2c_1: export PERIPH_I2C_MAX_BYTES_PER_FRAME

Success	Failures	Total	Runtime
6865	0	6865	16m:30s

Artifacts

• Documentation preview

[benpicco]

bors merge

[fabian18]

I have seen this too but I2C_CR2_NBYTES_Msk is defined by (almost) every stm32 so I don´t know why this limit exists for only a few of them

Nevermind its exactly those as in the Makefile and stm32h7

[fabian18]

Why not putting it to the corresponding periph_cpu.h files?

It would be more lines of change, and it seems to be equal for all according to the current code

BTW I'm wondering: Is BYTES_PER_FRAME really the correct wording for this in I2C terminology?

At least it is what was there before. What would be better?

[HendrikVE]

At least it is what was there before. What would be better?

To be honest I don't know^^ But I thought we are requesting multiple frames and not a single big one. But I really don't know I2C internals so I can't give a proposal on that

[bors]

Build succeeded:

• Murdock
• static-tests
• tools-build-success