Figure 4-2 Dma Read/Write Example - Nintendo Ultra64 Programmer's Manual

RSP Coprocessor 0
98
DMA Read/Write Example
Figure 4-2
###############################################
# Procedure to do DMA reads/writes.
# Registers:
# $20
# $19
# $18
# $17
# $11
.name mem_addr,
.name dram_addr,
.name dma_len,
.name iswrite,
.name tmp,
DMAproc: # request DMA access: (get semaphore)
DMAFull: # wait for not FULL:
# set DMA registers:
# handle writes:
DMAWrite:
DMADone:
.unname mem_addr
.unname dram_addr
.unname dma_len
.unname iswrite
.unname tmp
#
################################################
mem_addr
dram_addr
dma_len
iswrite?
used as tmp
$20
$19
$18
$17
$11
mfc0 tmp, SP_RESERVED
bne tmp, zero, DMAproc
# note delay slot
mfc0 tmp, DMA_FULL
bne tmp, zero, DMAFull
nop
mtc0 mem_addr, DMA_CACHE
bgtz iswrite, DMAWrite
mtc0 dram_addr, DMA_DRAM
j DMADone
mtc0 dma_len, DMA_READ_LENGTH
mtc0 dma_len, DMA_WRITE_LENGTH
jr return
# clear semaphore, delay slot
mtc0 zero, SP_RESERVED