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CHAPTER 8 INTERRUPT CONTROLLER
8.8 Example of Using the Hold Request Cancel Request
Function (HRCR)
When the CPU is to perform priority processing during DMA transfer, the DMA side
must cancel the hold request and release the CPU from the hold state. An example of
an interrupt occurring for DMA to cancel the hold request and allow CPU priority
operation is as follows.
■
Control Registers
❍
Hold request cancel request level register (HRCL): This module
When an interrupt having a level higher than that set in the HRCL register occurs, a hold
request cancel request is issued to DMA. Set the reference level for this operation.
❍
Interrupt control register (ICR): This module
Set a level higher than that set in the HRCL register in the ICR corresponding to the interrupt
cause used.
❍
Postpone DMA request register (PDRR): Clock controller
The PDRR is used to temporarily suppress a hold request from DMA and prevent the CPU from
returning to the hold state when the interrupt cause is cleared. A hold request from DMA is
transmitted to the CPU only when the value of this register is 0000
B
. Increment the value of this
register at the beginning of the interrupt routine and decrement it at the exit of the routine.
■
Hardware Configuration
A signal stream is shown below:
Figure 8.8-1 Example of Hardware Configuration for Using the Hold Request Cancel Request Function
IRQ (ICR) DMA CPU
(HRCL) HRCR DHRQ (PDRR) HRQ
This module
Clock controller
DHRQ: DMA hold request
HRQ: Hold request
IRQ: Interrupt request
HRCR: Hold request cancel request