STM32 SMBUS Stack Unexpected Behaviour
We're performing a block procedure call and struggled with odd SMBus-stack behaviour.
#define BLK_PRC_CALL ((uint8_t)0x90) /*!< Block process call - write, then read, variable sizes */
We incorrectly assumed the stack would read the response length from the slave after the initial write in the HAL_SMBUS_MasterRxCpltCallback. However, due to the conditional on line eight below, the receive length will be zero if you fail to set cmnd_master_RX_size in the st_command_t structure. The logic will ignore the returned length in pStackContext->Buffer[1] as it is always greater than cmnd_master_Rx_size (zero when not set).
stm32_SMBUS_stack.c HAL_SMBUS_MasterRxCpltCallback:307
/*
Reception next
Usually there is something left to be read, we continue on position 2 of the IO buffer
*/
pStackContext->StateMachine |= SMBUS_SMS_RECEIVE;
size = pStackContext->Buffer[1];
/* Applying upper limit on read size */
if ( size > pStackContext->CurrentCommand->cmnd_master_Rx_size )
{
size = pStackContext->CurrentCommand->cmnd_master_Rx_size;
}
HAL_SMBUS_Master_Receive_IT( hsmbus, pStackContext->SlaveAddress, &(pStackContext->Buffer[2]), (uint16_t)size,
SMBUS_LAST_FRAME_NO_PEC | ( pStackContext->StateMachine & SMBUS_SMS_PEC_ACTIVE ));
}
The application note (an4502) on page 18 makes no references to this field being mandatory for variable or fixed-length requests.
4.3.4 cmnd_master_Rx_size
Number of bytes transmitted in the slave response.
Is this an oversight in the documentation or a flaw in the SMBus stack?