31.5.2.13 Interrupt Status and Interrupts Arbitration

The Interrupt Status register stores all channels with pending interrupts, as shown below.

Figure 31-2. Interrupt Status Register

The Event System can arbitrate between all channels with pending interrupts. The arbiter can be configured to prioritize statically or dynamically the incoming events. The priority is evaluated each time a new channel has an interrupt pending, or an interrupt has been cleared. The Channel Pending Interrupt register (INTPEND) will provide the channel number with the highest interrupt priority, and the corresponding channel interrupt flags and status bits.

By default, static arbitration is enabled (PRICTRL.RRENx is '0'), the arbiter will prioritize a low channel number over a high channel number as shown below. When using the status scheme, there is a risk of high channel numbers never being granted access by the arbiter. This can be avoided using a dynamic arbitration scheme.

Figure 31-3. Static Priority

The dynamic arbitration scheme available in the Event System is round-robin. Round-robin arbitration is enabled by writing PRICTRL.RREN to one. With the round-robin scheme, the channel number of the last channel being granted access will have the lowest priority the next time the arbiter has to grant access to a channel, as shown below. The channel number of the last channel being granted access, will be stored in the Channel Priority Number bit group in the Priority Control register (PRICTRL.PRI).

Figure 31-4. Round-Robin Scheduling

The Channel Pending Interrupt register (INTPEND) also offers the possibility to indirectly clear the interrupt flags of a specific channel. Writing a flag to one in this register, will clear the corresponding interrupt flag of the channel specified by the INTPEND.ID bits.