md: implement subchannel processing for mcd (CD+G)

ares/md/mcd/cdd.cpp

@@ -60,6 +60,7 @@ auto MCD::CDD::advance() -> void {
     io.track = track();
     io.sector++;
     io.sample = 0;
+    readSubcode();
     return;
   }
 
@@ -93,6 +94,34 @@ auto MCD::CDD::position(s32 sector) -> double {
   return sqrt(sector / sectors * (outerRadius - innerRadius) + innerRadius) / radius;
 }
 
+auto MCD::CDD::readSubcode() -> void {
+  if(!mcd.fd) return;
+
+  mcd.fd->seek(((abs(mcd.cdd.session.leadIn.lba) + io.sector) * 2448) + 2352);
+  vector<u8> subchannel;
+  subchannel.resize(96);
+  mcd.fd->read({subchannel.data(), 96});
+
+  io.subcodePosition += 49;
+  n6 index = io.subcodePosition;
+
+  //subchannel data is stored by ares as 12x8 for each channel (PQRSTUVW)
+  //we need to convert this back to the raw subchannel encoding as per EMCA-130
+  for(int i = 0; i < 96; i+= 2) {
+    n16 data = 0;
+    for(auto channel : range(8)) {
+      n8 input = subchannel[(channel * 12) + (i / 8)];
+      n2 bits = input >> (6 - (i & 6));
+      data.bit( 7 - channel) = bits.bit(0);
+      data.bit(15 - channel) = bits.bit(1);
+    }
+
+    subcode[index++] = data;
+  }
+
+  mcd.irq.subcode.raise();
+}
+
 auto MCD::CDD::process() -> void {
 //if(command[0]) print("CDD ", command[0], ":", command[3], "\n");
 

ares/md/mcd/io-internal.cpp

@@ -176,8 +176,15 @@ auto MCD::readIO(n1 upper, n1 lower, n24 address, n16 data) -> n16 {
     data.bit(1,15) = gpu.vector.base.bit(3,17);
   }
 
+  if(address == 0xff8068) {
+    data.bit(0) = Unmapped;
+    data.bit(1,7) = cdd.io.subcodePosition.bit(0,6);
+    data.bit(8,15) = Unmapped;
+  }
+
   if(address >= 0xff8100 && address <= 0xff81ff) {
-    debug(unusual, "[MCD::readIO] address=0x", hex(address, 6L));
+    n6 index = address - 0xff8100 >> 1;
+    data = cdd.subcode[index];
   }
 
   return data;

ares/md/mcd/mcd.hpp

@@ -307,6 +307,7 @@ struct MCD : M68000, Thread {
     auto sample() -> void;
     auto position(s32 sector) -> double;
     auto process() -> void;
+    auto readSubcode() -> void;
     auto valid() -> bool;
     auto checksum() -> void;
     auto insert() -> void;
@@ -345,12 +346,14 @@ struct MCD : M68000, Thread {
       n16 sample;   //current audio sample# within current frame
       n7  track;    //current track#
       n1  tocRead;
+      n6  subcodePosition;
     } io;
 
     n1 hostClockEnable;
     n1 statusPending;
     n4 status [10];
     n4 command[10];
+    n16 subcode[64];
   } cdd;
 
   struct Timer {

ares/md/mcd/serialization.cpp

@@ -148,11 +148,13 @@ auto MCD::CDD::serialize(serializer& s) -> void {
   s(io.sample);
   s(io.track);
   s(io.tocRead);
+  s(io.subcodePosition);
 
   s(hostClockEnable);
   s(statusPending);
   s(status);
   s(command);
+  s(subcode);
 }
 
 auto MCD::Timer::serialize(serializer& s) -> void {

ares/md/system/serialization.cpp

@@ -1,4 +1,4 @@
-static const string SerializerVersion = "v134";
+static const string SerializerVersion = "v135";
 
 auto System::serialize(bool synchronize) -> serializer {
   if(synchronize) scheduler.enter(Scheduler::Mode::Synchronize);