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AD1848: Use the correct algorithm for CS423x ADPCM

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Still has level and DC offset issues, but actual use cases are lacking (all validation was done with ALSA's adpcm conversion plugin)
This commit is contained in:
RichardG867
2025-09-27 16:31:11 -03:00
parent bc41f8bbb6
commit 37eb2cb359
2 changed files with 48 additions and 24 deletions
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6
src/include/86box/snd_ad1848.h
View File

@@ -66,10 +66,10 @@ typedef struct ad1848_t {
uint8_t enable : 1;
uint8_t irq : 4;
uint8_t dma : 3;
uint8_t adpcm_ref;
int8_t adpcm_step;
int adpcm_predictor[2];
int16_t adpcm_step_index[2];
int freq;
int adpcm_data;
uint8_t adpcm_data;
int adpcm_pos;
uint8_t dma_ff;

66
src/sound/snd_ad1848.c
View File

@@ -56,9 +56,22 @@ ad1848_log(const char *fmt, ...)
static int ad1848_vols_7bits[128];
static double ad1848_vols_5bits_aux_gain[32];
/* Borrowed from snd_sb_dsp */
extern int8_t scaleMap4[64];
extern uint8_t adjustMap4[64];
/* Borrowed from ffmpeg. */
static const int8_t adpcm_index_table[16] = {
-1, -1, -1, -1, 2, 4, 6, 8,
-1, -1, -1, -1, 2, 4, 6, 8
};
static const int16_t adpcm_step_table[89] = {
7, 8, 9, 10, 11, 12, 13, 14, 16, 17,
19, 21, 23, 25, 28, 31, 34, 37, 41, 45,
50, 55, 60, 66, 73, 80, 88, 97, 107, 118,
130, 143, 157, 173, 190, 209, 230, 253, 279, 307,
337, 371, 408, 449, 494, 544, 598, 658, 724, 796,
876, 963, 1060, 1166, 1282, 1411, 1552, 1707, 1878, 2066,
2272, 2499, 2749, 3024, 3327, 3660, 4026, 4428, 4871, 5358,
5894, 6484, 7132, 7845, 8630, 9493, 10442, 11487, 12635, 13899,
15289, 16818, 18500, 20350, 22385, 24623, 27086, 29794, 32767
};
void
ad1848_setirq(ad1848_t *ad1848, int irq)
@@ -311,6 +324,8 @@ ad1848_write(uint16_t addr, uint8_t val, void *priv)
case 9:
if (!ad1848->enable && (val & 0x41) == 0x01) {
ad1848->adpcm_pos = 0;
ad1848->adpcm_predictor[0] = ad1848->adpcm_predictor[1] = 0;
ad1848->adpcm_step_index[0] = ad1848->adpcm_step_index[1] = 0;
ad1848->dma_ff = 0;
if (ad1848->timer_latch)
timer_set_delay_u64(&ad1848->timer_count, ad1848->timer_latch);
@@ -358,6 +373,11 @@ ad1848_write(uint16_t addr, uint8_t val, void *priv)
}
break;
case 17:
if (val & 0x08)
ad1848->adpcm_predictor[0] = ad1848->adpcm_predictor[1] = 0;
break;
case 18 ... 19:
if (ad1848->type >= AD1848_TYPE_CS4236B) {
if (ad1848->type >= AD1848_TYPE_CS4235) {
@@ -622,29 +642,33 @@ ad1848_dma_channel_read(ad1848_t *ad1848, int channel)
}
static int16_t
ad1848_process_adpcm(ad1848_t *ad1848)
ad1848_process_adpcm(ad1848_t *ad1848, int channel)
{
int temp;
if (ad1848->adpcm_pos++ & 1) {
temp = (ad1848->adpcm_data & 0x0f) + ad1848->adpcm_step;
temp = ad1848->adpcm_data >> 4;
} else {
ad1848->adpcm_data = (int) (ad1848_dma_channel_read(ad1848, ad1848->dma) & 0xffff);
temp = (ad1848->adpcm_data >> 4) + ad1848->adpcm_step;
ad1848->adpcm_data = ad1848_dma_channel_read(ad1848, ad1848->dma);
temp = ad1848->adpcm_data & 0x0f;
}
if (temp < 0)
temp = 0;
else if (temp > 63)
temp = 63;
ad1848->adpcm_ref += scaleMap4[temp];
if (ad1848->adpcm_ref > 0xff)
ad1848->adpcm_ref = 0xff;
else if (ad1848->adpcm_ref < 0x00)
ad1848->adpcm_ref = 0x00;
int step = adpcm_step_table[ad1848->adpcm_step_index[channel]];
int step_index = ad1848->adpcm_step_index[channel] + adpcm_index_table[temp];
if (step_index < 0)
step_index = 0;
else if (step_index > 88)
step_index = 88;
ad1848->adpcm_step = (int8_t) ((ad1848->adpcm_step + adjustMap4[temp]) & 0xff);
int diff = ((2 * (temp & 7) + 1) * step) >> 3;
int predictor = ad1848->adpcm_predictor[channel] + ((temp & 8) ? -diff : diff);
if (predictor < -32768)
predictor = -32768;
else if (predictor > 32767)
predictor = 32767;
ad1848->adpcm_predictor[channel] = predictor;
ad1848->adpcm_step_index[channel] = step_index;
return (int16_t) ((ad1848->adpcm_ref ^ 0x80) << 8);
return (int16_t) predictor;
}
static void
@@ -705,12 +729,12 @@ ad1848_poll(void *priv)
/* 0x80 and 0x90 reserved */
case 0xa0: /* Mono, 4-bit ADPCM */
ad1848->out_l = ad1848->out_r = ad1848_process_adpcm(ad1848);
ad1848->out_l = ad1848->out_r = ad1848_process_adpcm(ad1848, 0);
break;
case 0xb0: /* Stereo, 4-bit ADPCM */
ad1848->out_l = ad1848_process_adpcm(ad1848);
ad1848->out_r = ad1848_process_adpcm(ad1848);
ad1848->out_l = ad1848_process_adpcm(ad1848, 0);
ad1848->out_r = ad1848_process_adpcm(ad1848, 1);
break;
case 0xc0: /* Mono, 16-bit PCM big endian */