The symbols used
in
the-
state diagram are explained
in
the following list. Upper-case
names indicate external signals; lower-case names indicate local signals.
AUDxON
AUDxIP
AUDxIR
intreql
intreq2
AUDxDAT
AUDxDR
AUDxDSR
dmasen
percntrld
percount
perfin
lencntrld
lencount
lenfin
volcntrld
pbufldl
pbufld2
DMA
on
"x"
indicates channel number (signal from DMACON).
Audio interrupt pending (input
to
channel from interrupt circuitry).
Audio interrupt request (output from channel
to
interrupt
circuitry)
Interrupt request
that
combines with intreq2 to form AUDxIR
..
Prepare for interrupt request. Request comes
out
after the next
011-010
transition
in
normal operation.
Audio
data
load signal. Loads
16
bits of
data
to
audio channel.
Audio DMA request to Agnus for one word of data.
Audio
DMA
request to Agnus to reset pointer to
start
of block.
Restart request enable.
Reload period counter from back-up latch typically written by pro-
cessor with AUDxPER (can also be written by attach mode).
Count period counter down one latch.
Period counter finished (value
=
1)
..
Reload length counter from back-up latch.
Count length counter down one notch.
Length coun tel' finished (value
=
1).
Reload volume counter from back-up latch.
Load
output
buffer from holding latch written to by AUDxDAT.
Like pbufldl,
but
only during
010-011
with attach period.
162
Audio Hardware
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