Stopping The Audio Dma - Commodore Amiga Hardware Reference Manual

Table 5-3: D11A and Audio Channel Enable Bits
DMACON Register
Bit
Name
Function
15
SETCLR
When this bit is written as a 1, it
sets any bit in D11ACONW for which
the corresponding bit position is
also a 1, leaving all other bits alone.
9
D11AEN
Only while this bit is a 1 can
any
direct memory access occur.
3 . AUD3EN
Audio channel 3 enable .
2
AUD2EN Audio channel 2 enable.
1
AUDIEN
Audio channel 1 enable.
0 AUDOEN
Audio channel 0 enable.
For example, if you are using channel 0, then you write a
1
into bit 9 to enable D11A
and a 1 into bit 0 to enable the audio channel, as shown below.
SET EQU
AUDOEN EQU
D11AEN EQU
BEGINCHANO:
$08000
$01
$0200
MOVE.W #(SET
+
AUDOEN
+
D11AEN), D11ACONW
STOPPING THE AUDIO DMA
You can stop the channel by writing a 0 into the AUDxEN bit at any time. However,
you cannot resume the output at the same point in the waveform by just writing a
1
in
the bit again. Enabling an audio channel almost always starts the data output again
from the top of the list of data pointed to by the location registers for that channel. If
the channel is disabled for a very short time (less than two sampling periods) it may stay
on and thus continue from where it left off.
144 Audio Hardware