Mercurial > repos > blastem
diff ym2612.c @ 1798:5278b6e44fc1
Optionally emulate the offset around zero in the imperfect DAC of a discrete YM2612
| author | Michael Pavone <pavone@retrodev.com> |
|---|---|
| date | Sun, 24 Mar 2019 19:59:41 -0700 |
| parents | 804f13c090b4 |
| children | 1d1198f16279 |
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--- a/ym2612.c Sun Mar 24 13:31:22 2019 -0700 +++ b/ym2612.c Sun Mar 24 19:59:41 2019 -0700 @@ -256,6 +256,7 @@ } } ym_reset(context); + ym_enable_zero_offset(context, 1); } void ym_free(ym2612_context *context) @@ -267,8 +268,18 @@ free(context); } -#define YM_VOLUME_MULTIPLIER 2 -#define YM_VOLUME_DIVIDER 3 +void ym_enable_zero_offset(ym2612_context *context, uint8_t enabled) +{ + if (enabled) { + context->zero_offset = 0x70; + context->volume_mult = 79; + context->volume_div = 120; + } else { + context->zero_offset = 0; + context->volume_mult = 2; + context->volume_div = 3; + } +} #define YM_MOD_SHIFT 1 #define CSM_MODE 0x80 @@ -549,7 +560,7 @@ if (value & 0x2000) { value |= 0xC000; } - dfprintf(debug_file, "channel %d output: %d\n", channel, (value * YM_VOLUME_MULTIPLIER) / YM_VOLUME_DIVIDER); + dfprintf(debug_file, "channel %d output: %d\n", channel, (value * context->volume_mult) / context->volume_div); } } //puts("operator update done"); @@ -571,14 +582,19 @@ value |= 0xC000; } } + if (value >= 0) { + value += context->zero_offset; + } else { + value -= context->zero_offset; + } if (context->channels[i].logfile) { fwrite(&value, sizeof(value), 1, context->channels[i].logfile); } if (context->channels[i].lr & 0x80) { - left += (value * YM_VOLUME_MULTIPLIER) / YM_VOLUME_DIVIDER; + left += (value * context->volume_mult) / context->volume_div; } if (context->channels[i].lr & 0x40) { - right += (value * YM_VOLUME_MULTIPLIER) / YM_VOLUME_DIVIDER; + right += (value * context->volume_mult) / context->volume_div; } } render_put_stereo_sample(context->audio, left, right);