clear mapped RAM on subsong change

On a subsong change the player has to reset the CPU, registers, RAM
etc.

Until now the mapped external cartridge RAM was not reset, which could
make state from one subsong spill over into the next.  Depending on
the player routine and subsong sequence this could lead to playback
errors.

This fixes issue #124.

HISTORY

@@ -10,6 +10,8 @@ Bugfixes:
 - gbs core:
   - fix noise channel LSFR for more faithful drumtracks in most ROMs
   - fix generated MIDI files being ~1.5% too slow
+  - reset cartridge RAM on subsong change to prevent the state of a
+    subsong from influencing later subsongs
 
 - gbsplay
   - fix display of unknown version number (gbsplay -V)

gbs.c

@@ -242,6 +242,8 @@ long gbs_init(struct gbs* const gbs, long subsong)
 	struct gbcpu *gbcpu = &gbhw->gbcpu;
 
 	gbhw_init(gbhw);
+	if (gbs->mapper)
+		mapper_init(gbs->mapper);
 
 	if (subsong == -1) subsong = gbs->defaultsong - 1;
 	if (subsong >= gbs->songs) {

mapper.c

@@ -254,3 +254,7 @@ struct mapper *mapper_gb(struct gbcpu *gbcpu, const uint8_t *rom, size_t size, u
 void mapper_free(struct mapper *m) {
 	free(m);
 }
+
+void mapper_init(struct mapper *m) {
+	memset(m->ram, 0, sizeof(m->ram));
+}

mapper.h

@@ -19,5 +19,6 @@ struct mapper *mapper_gbr(struct gbcpu *gbcpu, const uint8_t *rom, size_t size,
 struct mapper *mapper_gb(struct gbcpu *gbcpu, const uint8_t *rom, size_t size, uint8_t cart_type, uint8_t rom_type, uint8_t ram_type);
 void mapper_lockout(struct mapper *m);
 void mapper_free(struct mapper *m);
+void mapper_init(struct mapper *m);
 
 #endif