
Decompression
Algorithm
Resources Used
Maximum
Sampling
Rate
Possible
Combined
Algorithms
RAM
ROM,
total
ROM, last
page
3-bit ADPCM
18
333
49
8.0kHz
ADPCM3,
PCM6, PCM8
3-bit ADPCM,
QUICK
15
459
196
11.0kHz
ADPCM3,
PCM6, PCM8
4-bit ADPCM
17
309
32
7.5kHz
ADPCM4,
PCM6, PCM8
4-bit ADPCM,
QUICK
14
509
256
11.0kHz
ADPCM4,
PCM6, PCM8
PCM
12
186
0
16.0kHz
PCM6, PCM8
Table: The decompressing algorithms and the resources used.
Each of these decompressing algorithms is implemented in an interrupt
service routine and shall be invoked each time the sampling rate counter
overflows. In these decompressing algorithms, the voice ROM data is
accessed, the decompressing action is taken and the decompressed data is
then sent to the D/A output.
Since there is no other function called in the decompressing algorithms, the
ISR could be invoked once when the sampling rate counter overflows and
the stack is not full. In the ISR, the value of the accumulator and the status
registers are preserved but the value of the following registers might be
changed: TBLP(07H), TBLH(08H), DAL(20H), DAH(21H), ROMC(2CH).
Important
Since the registers TBLP and TBLH might be changed in the ISR, it is
important to disable the sampling rate interrupt when using table lookup
instructions TABRDC or TABRDL.
→
Decompression algorithms usage
If it is required to use all of these decompression algorithms, the file
’voice.inc’ must be included and then the ISR specified for the sampling rate
counter interrupt in the program. Any other resources supported are in-
tended to assist with customising the sound track playing. A sample pro-
gram follows to explain this ...
; t.asm
; 1
;
; 2
#include voice.inc
; 3 include file ’voice.inc’
code .section at 0 ’code’
; 4
org
0
; 5
jmp
begin
; 6
Chapter 13
µ
C VROM Editor (HT-VDS827)
149
Содержание HT-IDE
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