Hands-On RTOS with Microcontrollers

Guaranteeing atomic transactions

Sometimes, it is desirable to transmit a message and then be confident that the response is for that message. In these cases, a mutex can be used at a higher level. This allows for groups of messages to be clustered together. An example of when this technique can be especially useful is a single peripheral servicing multiple physical ICs across multiple tasks:

In the preceding diagram, the same peripheral (SPI1) is used to service two different ICs. Although the SPI peripheral is shared, there are separate chip select lines (CS1 and CS2) for each IC. There are also two completely independent drivers for these ...