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I2C

In STM32CubeMX, the I2C runs in I2C mode, with the matching DMA channels and interrupts configured. An instance in SMBus mode uses an SMBUS handle; it gets no object, and libxr parse warns about it.

Example​

The last constructor argument is the DMA switching threshold. The relevant branch requires the transfer length to be strictly greater than this value. With threshold 3, a three-byte transfer does not enter the DMA branch; four bytes does.

static STM32I2C i2c1(&hi2c1, i2c1_buf, 3);

Configuration File​

After code generation, the following I2C section appears in User/libxr_config.yaml:

I2C:
  i2c1:
    buffer_size: 32
    dma_section: ''
    dma_enable_min_size: 3
  • buffer_size: shared I2C transfer / receive buffer size
  • dma_section: linker section for the generated buffer declaration
  • dma_enable_min_size: DMA switching threshold; only a transfer longer than this value enters the DMA branch

Generation rules:

  • each I2C instance gets one buffer shared by transmit and receive, for example i2c1_buf, of buffer_size bytes;
  • dma_enable_min_size is the last argument of the STM32I2C constructor;
  • dma_section decides the section the buffer goes to, see Cache;
  • FMPI2C peripherals get no object and libxr parse warns about them; LibXR has no FMPI2C driver.

After editing the file, regenerate the code with the commands in Regenerating the Code.