Example Of Using The Hold Request Cancellation Request Function (Hrcr) - Fujitsu MB91319 Series Hardware Manual

CHAPTER 9 INTERRUPT CONTROLLER
9.4 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
❍ Hold request cancellation level setting register (HRCL): This module
If an interrupt with a higher interrupt level than the level defined in this register occurs, a hold
request cancellation request is issued to DMA. This register sets the level to be used as the
criterion for this purpose.
❍ ICR: This module
This register sets a higher level than the level in the HRCL register for the ICR corresponding to
the interrupt source that will be used.
■ Hardware Configuration
Figure 9.4-1 shows the flow of signals.
This module
IRQ MHALTI
I-UNIT
(ICR)
(HRCL)
214
Figure 9.4-1 Flow of Signals
Bus access request
DMA B-UNIT
DHREQ: D bus hold request
DHREQ
CPU DHACK: D bus hold acknowledge
IRQ: Interrupt request
MHALTI: Hold request
DHACK
cancellation request