SAB82538 Datasheet, PDF (42/253 Pages) Infineon Technologies AG – ICs for Communications

SAB 82538
SAF 82538
Interrupt priority mode 2: Rotating priority of 8 channels
With IVA.ROT = 1 and IPC.ROTM = 0 the interrupt priority rotation mode is selected.
After an interrupt has been serviced the priorities of all eight channels are rotated
cyclically so that the channel last serviced is assigned the lowest priority of all. The
ESCC8 will adjust the priorities according to the following scheme.
Example:
Suppose the order of the channels is as follows with descending priority from left to right:
0 1 2 3 4 5 6 7 pp (pp = parallel port interrupt)
Suppose channel 4 requires interrupt service and no other channel / interrupt group with
higher priority is or becomes active, so that channel 4 has the currently highest priority
of all channels at the time when the interrupt vector is output. After the interrupt in
question has been acknowledged, an automatic reordering of the channels (and of
pending interrupts, if any) takes place so that channel 4 is given the lowest channel
priority. The relative ordering of the channels remains the same:
5 6 7 0 1 2 3 4 pp
This interrupt priority rotation guarantees fair treatment of all the channels. A reordering
of the interrupts takes also place when any other channel interrupt is acknowledged by
reading a corresponding interrupt status register, so that the corresponding channel is
put behind the others.
Note: Parallel ports have always lowest priority.
Semiconductor Group
42