mpeg_audio.cpp/ymz770.cpp: add decode of "AMMSL" type samples for YMZ770B

src/devices/sound/mpeg_audio.cpp

@@ -32,7 +32,7 @@ void mpeg_audio::clear()
 }
 
 bool mpeg_audio::decode_buffer(int &pos, int limit, short *output,
-								int &output_samples, int &sample_rate, int &channels)
+								int &output_samples, int &sample_rate, int &channels, int atbl)
 {
 	if(limit - pos < 16)
 		return false;
@@ -44,6 +44,7 @@ bool mpeg_audio::decode_buffer(int &pos, int limit, short *output,
 
 	current_pos = pos;
 	current_limit = limit;
+	cbr_param_index = atbl;
 	unsigned short sync = do_gb(base, current_pos, 12);
 
 	retry_sync:
@@ -124,15 +125,24 @@ bool mpeg_audio::decode_buffer(int &pos, int limit, short *output,
 
 void mpeg_audio::read_header_amm(bool layer25)
 {
-	gb(1); // unused
+	int ammsl = gb(1); // 1 = older AMM variant, CBR and constant frame size
 	int full_packets_count = gb(4); // max 12
 	int srate_index = gb(2); // max 2
 	sampling_rate = srate_index + 4 * layer25;
 	int last_packet_frame_id = gb(2); // max 2
-	last_frame_number = 3*full_packets_count + last_packet_frame_id;
 	int stereo_mode = gb(2);
 	int stereo_mode_ext = gb(2);
-	param_index = gb(3);
+	if (ammsl)
+	{
+		last_frame_number = 36;
+		param_index = cbr_param_index; // CBR, param_index came from sample pointer top bits
+		gb(3);
+	}
+	else
+	{
+		last_frame_number = 3*full_packets_count + last_packet_frame_id;
+		param_index = gb(3);
+	}
 	gb(1); // must be zero
 
 	channel_count = stereo_mode != 3 ? 2 : 1;

src/devices/sound/mpeg_audio.h

@@ -38,6 +38,7 @@ public:
 	// output_samples = number of samples written to output per channel
 	// sample_rate    = output sample rate
 	// channels       = number of channels written to output (total sample count is output_samples*channels)
+	// atbl           = parameters index for older AMMSL CBR samples
 	//
 	// returns true if the buffer was complete and the new position in pos, false otherwise
 	//
@@ -50,7 +51,7 @@ public:
 	// 1152 in the amm case, <1152 indicating end of stream).
 
 	bool decode_buffer(int &pos, int limit, short *output,
-						int &output_samples, int &sample_rate, int &channels);
+						int &output_samples, int &sample_rate, int &channels, int atbl = 0);
 
 
 	// Clear audio buffer
@@ -80,7 +81,7 @@ private:
 	int accepted, position_align;
 
 	int sampling_rate, last_frame_number;
-	int param_index;
+	int param_index, cbr_param_index;
 
 	int channel_count, total_bands, joint_bands;
 

src/devices/sound/ymz770.cpp

@@ -2,17 +2,17 @@
 // copyright-holders:Olivier Galibert, R. Belmont, MetalliC
 /***************************************************************************
 
-    Yamaha YMZ770C "AMMS-A" and YMZ774 "AMMS2C"
+    Yamaha YMZ770B "AMMSL", YMZ770C "AMMS-A" and YMZ774 "AMMS2C"
 
     Emulation by R. Belmont and MetalliC
     AMM decode by Olivier Galibert
 
 -----
 TODO:
-- What does channel ATBL mean?
 - Simple Access mode. SACs is register / data lists same as SEQ. in 770C, when both /SEL and /CS pins goes low - will be run SAC with number set at data bus.
   can not be used in CV1K (/SEL pin is NC, internally pulled to VCC), probably not used in PGM2 too.
  770:
+- Configurable clock (currently hardcoded at 16kHz)
 - sequencer timers implemented but seems unused, presumably because of design flaws or bugs, likely due to lack of automatic adding of sequencer # to register offset.
   in result sequences uses very long chains of 32-sample wait commands instead, wasting a lot of ROM space.
 - sequencer triggers not implemented, not sure how they works (Deathsmiles ending tune starts sequence with TGST = 01h, likely a bug and don't affect tune playback)
@@ -23,7 +23,7 @@ TODO:
 - sequencer off trigger (not used in games)
 
  known SPUs in this series:
-  YMZ770B  AMMSL    Capcom medal hardware (alien.cpp), sample format is not AMM, in other parts looks like 770C
+  YMZ770B  AMMSL    Capcom medal hardware (alien.cpp)
   YMZ770C  AMMS-A   Cave CV1000
   YMZ771   SSGS3
   YMZ773   AMMS2    Cron corp. video slots
@@ -236,7 +236,7 @@ retry:
 				{
 					// next block
 					int sample_rate, channel_count;
-					if (!channel.decoder->decode_buffer(channel.pptr, m_rom.bytes()*8, channel.output_data, channel.output_remaining, sample_rate, channel_count) || channel.output_remaining == 0)
+					if (!channel.decoder->decode_buffer(channel.pptr, m_rom.bytes()*8, channel.output_data, channel.output_remaining, sample_rate, channel_count, channel.atbl) || channel.output_remaining == 0)
 					{
 						channel.is_playing = !channel.last_block; // detect infinite retry loop
 						channel.last_block = true;