Semaphore coding method to ensure data integrity in a can microcontroller and a can microcontroller that implements this method

摘要

A method for use in a CAN device (e.g., a CAN microcontroller) that includes a processor core and hardware external to the processor core (e.g., a DMA engine) that writes message data into a designated message buffer for ensuring integrity of the message data stored in the designated message buffer. The method includes providing a three-state semaphore to indicate a current access status of the designated message buffer, the three-state semaphore having a first state indicative of the hardware external to the processor core starting to write new message data into the designated message buffer, a second state indicative of the hardware external to the processor core having finished writing the new message data into the designated message buffer, and, a third state indicative of the processor core starting to read message data from the designated message buffer. The processor core determines whether the designated message buffer is ready to be accessed based on the current state of the semaphore. The processor core, after determining that the designated message buffer is ready to be accessed, reads the message data from the designated message buffer. After the processor core has finished reading the message data from the designated message buffer, it checks the current state of the semaphore to determine whether it has changed to a different state during the time that the processor core was reading the message data from the designated message buffer. If the processor core determines that the current state of the semaphore changed during the time that the processor core was reading the message data from the designated message buffer, it again determines whether the designated message buffer is ready to be accessed, based on the current state of the semaphore. After again determining that the designated message buffer is ready to be accessed, the processor core again reads the message data from the designated message buffer.