SPRUIZ1B July 2023 – August 2024 TMS320F28P650DH , TMS320F28P650DK , TMS320F28P650SH , TMS320F28P650SK , TMS320F28P659DH-Q1 , TMS320F28P659DK-Q1 , TMS320F28P659SH-Q1
For every PIE group, the low-number channels in the group have the highest priority. For instance in PIE group 1, channel 1.1 has priority over channel 1.3. If those two enabled interrupts occurred simultaneously, channel 1.1 is serviced first with channel 1.3 left pending. Once the ISR for channel 1.1 completes and provided there are no other enabled and pending interrupts for PIE group 1, channel 1.3 is serviced. However, for the CPU to service any more interrupts from a PIE group, PIEACK for the group must be cleared. For this specific example, for channel 1.3 to be serviced, channel 1.1’s ISR has to clear PIEACK for group 1.
The following example describes an alternative scenario: channel 1.1 is currently being serviced by the CPU, channel 1.3 is pending and before channel 1.1’s ISR completes, channel 1.2 that is enabled also comes in. Since channel 1.2 has a higher priority than channel 1.3, the CPU services channel 1.2 and channel 1.3 remains pending. Using the steps from the Interrupt Entry Sequence (Section 3.4.3), channel 1.2 interrupt can happen as late as step 10 (The CPU fetches the ISR vector from the PIE. PIEIFRx.y is cleared) and the channel 1.2 interrupt is serviced ahead of channel 1.3.