Example Of Using The Hold Request Cancellation Request Function (Hrcr) - Fujitsu FR60 Hardware Manual

11.4 Example of Using the Hold Request Cancellation Request
Function (HRCR)
To allow the CPU to perform high-priority processing during DMA transfer, cancel a
hold request for DMA and clear the hold state. In this example, an interrupt is used to
cancel a hold request to the DMA, allowing the CPU to perform priority operations.
■ Control Registers
❍ HRCL (hold request cancellation request level setting register):
If an interrupt with a higher interrupt level than the level in the HRCL register occurs, a hold
request cancellation request is generated for DMA. This register sets the level to be used as the
criterion for this purpose.
❍ ICR:
This register sets a level higher than the level in the HRCL register for the ICR corresponding to
the interrupt source that will be used.
■ Hardware Configuration
The flow of signals is as follows.
This module
IRQ MHALTI
I-UNIT
(ICR)
(HRCL)
Figure 11.4-1 Flow of Signals
Bus access request
DMA B-UNIT
CHAPTER 11 INTERRUPT CONTROLLER
DHREQ: D-bus hold request
DHREQ
CPU DHACK: D-bus hold acknowledge
IRQ: Interrupt request
MHALTI: Hold request
DHACK
cancellation request
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