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[SCD] improved synchronization between PCM chip & SUB-CPU (Willy Beamish)

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[SCD] fixed PCM waveform sign bit and output precision
This commit is contained in:
EkeEke 2012-08-26 21:11:15 +02:00
parent 2cec58e50a
commit c8d4bb4f91
2 changed files with 59 additions and 15 deletions
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73
source/cd_hw/pcm.c
View File

@ -38,7 +38,7 @@
#include "shared.h"
#include "blip.h"
#define PCM_CLOCKS_PER_SAMPLE (384 * 4)
#define PCM_MCLOCKS_PER_SAMPLE (384 * 4)
#define pcm scd.pcm_hw
@ -49,8 +49,8 @@ void pcm_init(double clock, double samplerate)
pcm_shutdown();
/* allocate blip buffers */
blip[0] = blip_alloc(clock, samplerate * PCM_CLOCKS_PER_SAMPLE, samplerate / 4);
blip[1] = blip_alloc(clock, samplerate * PCM_CLOCKS_PER_SAMPLE, samplerate / 4);
blip[0] = blip_alloc(clock, samplerate * PCM_MCLOCKS_PER_SAMPLE, samplerate / 4);
blip[1] = blip_alloc(clock, samplerate * PCM_MCLOCKS_PER_SAMPLE, samplerate / 4);
}
void pcm_shutdown(void)
@ -69,16 +69,19 @@ void pcm_reset(void)
/* reset default bank */
pcm.bank = pcm.ram;
/* reset master clocks counter */
pcm.cycles = 0;
/* clear blip delta buffers */
blip_clear(blip[0]);
blip_clear(blip[1]);
}
void pcm_update(short *buffer, int length)
void pcm_run(unsigned int length)
{
/* get number of clocks needed */
length = blip_clocks_needed(blip[0], length);
#ifdef LOG_PCM
error("[%d][%d]run %d PCM samples (from %d)\n", v_counter, s68k.cycles, length, pcm.cycles);
#endif
/* check if PCM chip is running */
if (pcm.enabled)
{
@ -117,16 +120,21 @@ void pcm_update(short *buffer, int length)
/* infinite loop should not output any data */
if (data != 0xff)
{
/* output L & R subchannels */
/* check sign bit (output centered around 0) */
if (data & 0x80)
{
/* PCM data is positive */
data = data & 0x7f;
}
else
{
/* PCM data is negative */
data = -(data & 0x7f);
}
/* multiply PCM data with ENV & stereo PAN data then add to outputs (13.6 fixed point) */
l += ((data * pcm.chan[j].env * (pcm.chan[j].pan & 0x0F)) >> 6);
r += ((data * pcm.chan[j].env * (pcm.chan[j].pan >> 4)) >> 6);
/* multiply PCM data with ENV & stereo PAN data then add to L/R outputs (14.5 fixed point) */
l += ((data * pcm.chan[j].env * (pcm.chan[j].pan & 0x0F)) >> 5);
r += ((data * pcm.chan[j].env * (pcm.chan[j].pan >> 4)) >> 5);
}
}
}
@ -169,17 +177,43 @@ void pcm_update(short *buffer, int length)
}
}
/* resample to output stereo buffer */
/* end of blib buffer frame */
blip_end_frame(blip[0], length);
blip_read_samples(blip[0], buffer, 1);
blip_end_frame(blip[1], length);
/* update PCM master clock counter */
pcm.cycles += length * PCM_MCLOCKS_PER_SAMPLE;
}
void pcm_update(short *buffer, int length)
{
/* get number of internal clocks (samples) needed */
unsigned int clocks = blip_clocks_needed(blip[0], length);
/* run PCM chip */
pcm_run(clocks);
/* resample to output stereo buffer */
blip_read_samples(blip[0], buffer, 1);
blip_read_samples(blip[1], buffer + 1, 1);
/* reset PCM master clocks counter */
pcm.cycles = 0;
}
void pcm_write(unsigned int address, unsigned char data)
{
/* synchronize PCM chip with SUB-CPU */
int clocks = s68k.cycles - pcm.cycles;
if (clocks > 0)
{
/* number of internal clocks (samples) to run */
clocks = (clocks + PCM_MCLOCKS_PER_SAMPLE - 1) / PCM_MCLOCKS_PER_SAMPLE;
pcm_run(clocks);
}
#ifdef LOG_PCM
error("[%d][%d]PCM %x write -> 0x%02x (%X)\n", v_counter, s68k.cycles, address, data, s68k.pc);
error("[%d][%d]PCM write %x -> 0x%02x (%X)\n", v_counter, s68k.cycles, address, data, s68k.pc);
#endif
/* external RAM is mapped to $1000-$1FFF */
@ -293,8 +327,17 @@ void pcm_write(unsigned int address, unsigned char data)
unsigned char pcm_read(unsigned int address)
{
/* synchronize PCM chip with SUB-CPU */
int clocks = s68k.cycles - pcm.cycles;
if (clocks > 0)
{
/* number of internal clocks (samples) to run */
clocks = (clocks + PCM_MCLOCKS_PER_SAMPLE - 1) / PCM_MCLOCKS_PER_SAMPLE;
pcm_run(clocks);
}
#ifdef LOG_PCM
error("[%d][%d]PCM %x read (%X)\n", v_counter, s68k.cycles, address, s68k.pc);
error("[%d][%d]PCM read (%X)\n", v_counter, s68k.cycles, address, s68k.pc);
#endif
/* external RAM (TODO: verify if possible to read, some docs claim it's not !) */

1
source/cd_hw/pcm.h
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@ -59,6 +59,7 @@ typedef struct
uint8 status; /* channels ON/OFF status */
uint8 index; /* current channel index */
uint8 ram[0x10000]; /* 64k external RAM */
uint32 cycles;
} pcm_t;
/* Function prototypes */