Figure 4-5 Outputopen Function Using The Xbus - Nintendo Ultra64 Programmer's Manual

RSP Coprocessor 0
102
OutputOpen Function Using the XBUS
Figure 4-5
.name dmemp,
.name dramp,
.name outsz,
# open(size)
#
#
#
#
OutputOpen: # check if the packet will fit in the buffer
WrapBuffer: # packet won't fit, wait for current to wrap
AdvanceCurrent:
CurrentFit: # done if current_address <= outp
# loop if current_address <= (outp + outsz)
OpenDone:
$20
$19
$18 # caller sets to max size of write
- wait for size avail in
ring buffer.
- possibly handle wrap
- wait for 'current' to get
out of the way
.ent OutputOpen
addi dramp, zero, (RSP_OUTPUT_OFFSET
+ RSP_OUTPUT_SIZE8)
add dmemp, outp, outsz
sub dramp, dramp, dmemp
bgez dramp, CurrentFit
nop
mfc0 dramp, CMD_STATUS
andi dramp, dramp, 0x0400
bne dramp, zero, WrapBuffer
# wait for current to advance
mfc0 dramp, CMD_CURRENT
addi outp, zero, RSP_OUTPUT_OFFSET
beq dramp, outp, AdvanceCurrent
nop
mtc0 outp, CMD_START
mfc0 dramp, CMD_CURRENT
sub dmemp, outp, dramp
bgez dmemp, OpenDone
add dmemp, outp, outsz
sub dramp, dmemp, dramp
bgez dramp, CurrentFit
nop
jr return
nop
.end OutputOpen
# reset START