Overview - Fujitsu MB96300 series Hardware Manual

CHAPTER 4 DMA
4.1

Overview

DMA enables automatic data transfer between memory and memory/peripheral resource
registers or vice versa without interaction of the CPU. DMA replaces 16LX family's EI
while offering the extended functionality at higher performance.
This section describes the DMA functions.
■ DMA compared to interrupt handling:
DMA has the following advantages compared to handling the transfer via interrupt (see Figure 4.1-1):
• DMA reduces CPU processing load for interrupt handling
• No CPU register is used for the transfer, eliminating the need for register saving, which increases the
transfer speed.
• The CPU bus is only used for the transfer operation itself. As consequence, the transfer speed is increased.
Figure 4.1-1 Comparison of interrupt handling by CPU and by DMA (principle only, number of clock cycles
Case A: Interrupt handling and data transfer by CPU
CLKB
Interrupt
CPU
main program
INT
execution
Case B: Interrupt handling and data transfer by DMA
CLKB
Interrupt
DMA
Data
transfer
CPU
main program
wait
execution
■ DMA functions
The DMA controller has the following functions:
116
may differ depending on the program code)
Stack
Data source/dest.
operation address calculation
CPU busy with handling interrupt
Interrupt is cleared by DMA w/o bus transfer
main program execution
CPU waiting while DMA performs interrupt handling
(During this time CPU may execute code from the prefetch queue)
MB96300 Super Series Hardware Manual
Data Stack
Clear interrupt
transfer operation
2
OS
main program
RETI
execution