ref: d1cebf608b05e45b148108ac6c16ae94f6862097
dir: /sys/src/games/2600/aud.c/
#include <u.h> #include <libc.h> #include "dat.h" #include "fns.h" static int sdiv[2], fdiv[2], cdiv[2], ch[2], sr[2] = {-1,-1}; static short sbuf[2000*2], *sbufp; static int audfd; #define div(n) if(++cdiv[i] < n) break; cdiv[i] = 0 static void channel(int i) { sdiv[i] += HZ/114; for(; sdiv[i] >= RATE; sdiv[i] -= RATE) if(fdiv[i] >= (reg[AUDF0 + i] & 31)){ fdiv[i] = 0; switch(reg[AUDC0 + i] & 15){ case 0: ch[i] = 1; break; case 2: div(15); case 1: ch[i] = sr[i] & 1; sr[i] = sr[i] >> 1 & 7 | (sr[i] << 2 ^ sr[i] << 3) & 8; break; case 4: case 5: ch[i] ^= 1; break; case 12: case 13: div(3); ch[i] ^= 1; break; case 6: case 10: div(16); ch[i] ^= 1; break; case 14: div(46); ch[i] ^= 1; break; case 15: div(3); case 7: case 9: ch[i] = sr[i] & 1; sr[i] = sr[i] >> 1 & 15 | (sr[i] << 2 ^ sr[i] << 4) & 16; break; case 8: ch[i] = sr[i] & 1; sr[i] = sr[i] >> 1 & 255 | (sr[i] << 4 ^ sr[i] << 8) & 256; break; case 3: ch[i] = sr[i] & 1; sr[i] = sr[i] & 15 | sr[i] >> 1 & 240 | (sr[i] << 2 ^ sr[i] << 3) & 256; if((sr[i] & 256) != 0) sr[i] = sr[i] & 496 | sr[i] >> 1 & 7 | (sr[i] << 2 ^ sr[i]) << 3 & 8; break; } }else fdiv[i]++; } void sample(void) { int d; if(sbufp == nil) return; channel(0); channel(1); d = ch[0] * (reg[AUDV0] & 15) + ch[1] * (reg[AUDV1] & 15); if(sbufp < sbuf + nelem(sbuf) - 1){ *sbufp++ = d * 1000; *sbufp++ = d * 1000; } } int audioout(void) { int rc; if(sbufp == nil) return -1; if(sbufp == sbuf) return 0; rc = write(audfd, sbuf, (sbufp - sbuf) * 2); if(rc > 0) sbufp -= (rc+1)/2; if(sbufp < sbuf) sbufp = sbuf; return 0; } void initaudio(void) { audfd = open("/dev/audio", OWRITE); if(audfd < 0) return; sbufp = sbuf; }