IPC — Interprocessor communication

The following figure illustrates the IPC peripheral in a multi-MCU system, where each MCU has one dedicated IPC peripheral. The IPC peripheral can be used to send and receive events to and from other IPC peripherals.

Figure 1. IPC block diagram

An instance of the IPC peripheral can have multiple SEND tasks and RECEIVE events. A single SEND task can be configured to signal an event on one or more IPC channels, and a RECEIVE event can be configured to listen on one or more IPC channels. The IPC channels that are triggered in a SEND task can be configured through the SEND_CNF registers, and the IPC channels that trigger a RECEIVE event are configured through the RECEIVE_CNF registers. The figure below illustrates how the SEND_CNF and RECEIVE_CNF registers work. Both the SEND task and the RECEIVE event can be connected to all IPC channels.

Figure 2. IPC registers SEND_CNF and RECEIVE_CNF

A SEND task can be viewed as broadcasting events onto one or more IPC channels, and a RECEIVE event can be seen as subscribing to a subset of IPC channels. It is possible for multiple IPCs to trigger events onto the same PPI channel at the same time. When two or more events on the same channel occur within t_IPC, the events may be merged into a single event seen from the IPC receiver. One of the events can therefore be lost. To prevent this, the user must ensure that events on the same IPC channel do not occur within t_IPC of each other. When implementing firmware data structures, such as queues or mailboxes, this can be done by using one IPC channel for acknowledgements.

An IPC event often does not contain any data itself, it is used to signal other MCUs that something has occurred. Data can be shared through shared memory, for example in the form of a software implemented mailbox, or command/event queues. It is up to software to assign a logical functionality to an IPC channel. For instance, one IPC channel can be used to signal that a command is ready to be executed, and any processor in the system can subscribe to that particular IPC channel and decode/execute the command.

General purpose memory

The GPMEM registers can be used freely to store information. These registers are accessed like any other of the IPC peripheral's registers. Note that the contents of the GPMEM registers are not shared between the instances of the peripherals. I.e. writing the GPMEM register of one peripheral does not change the value in another.