Commodore Amiga - Telling the System about the Data

Table 5-1: Sample Audio Data Set for Channel 0
audiodata
--- >
AUDOLC *
100
98
AUDOLC + 2 **
92 83
AUDOLC +4
71
56
AUDOLC + 6
38
20
AUDOLC +8 0
-20
AUDOLC + 10
-38 -56
AUDOLC + 12
-71
-83
AUDOLC + 14
-92 -83
AUDOLC + 16
-100
-98
AUDOLC + 18
-92
-83
AUDOLC + 20
-71
-56
AUDOLC + 22 -38
-20
AUDOLC + 24
0
20
AUDOLC + 26 38
56
AUDOLC + 28 71 83
AUDOLC + 30
92 98
Notes
*
Audio data is located on a word-address boundary.
**
AUDOLC stands for AUDOLCL and AUDOLCH.
TELLING THE SYSTEM ABOUT THE DATA
In order to retrieve the sound data for the audio channel, the system needs to know
where the
data is located and how long (in words) the data is.
The location registers AUDxLCH and AUDxLCL contain the high three bits and the low
fifteen bits, respectively, of the starting address of the audio data. Since these two regis-
ter addresses are contiguous, writing a long word into AUDxLCH moves the audio
data
address into both locations. The "x" in the register names stands for the number of the
audio channel where the
output will occur. The channels are numbered 0, I, 2, and 3.
These registers are location registers, as distinguished from pointer registers. You need
to specify the contents of these registers only once; no resetting is necessary when you
wish the audio channel to keep on repeating the same waveform. Each time the system
retrieves the last audio word from the
data area, it uses the contents of these location
registers
to again find the start of the data. Assuming the first word of data starts at
138 Audio Hardware