add simple drum loop to menu music

src/gbprinter.h

 #include <stdint.h>
 
 enum PRN_STATUS {
+    // status flags from printer
     PRN_STATUS_LOWBAT      = 0x80, // battery too low
     PRN_STATUS_ER2         = 0x40, // unspecified error
     PRN_STATUS_ER1         = 0x20, // paper jam
     PRN_STATUS_UNTRAN      = 0x08, // unprinted data in buffer
     PRN_STATUS_FULL        = 0x04, // ready, triggered by DATA with len 0
     PRN_STATUS_BUSY        = 0x02, // printer is printing
-    PRN_STATUS_CHECKSUM    = 0x01, // Checksum error
-    PRN_STATUS_OK          = 0x00,
+    PRN_STATUS_CHECKSUM    = 0x01, // checksum error
+    PRN_STATUS_OK          = 0x00, // everything is fine
 
-    PRN_STATUS_CANCELLED   = 0x100,
-    PRN_STATUS_TIMEOUT     = 0x200,
-    PRN_STATUS_NO_MAGIC    = 0x400,
+    // status flags from driver code
+    PRN_STATUS_CANCELLED   = 0x100, // user has aborted the print by pressing B
+    PRN_STATUS_TIMEOUT     = 0x200, // timeout waiting for printer response
+    PRN_STATUS_NO_MAGIC    = 0x400, // printer did not respond with proper 'alive'
 
+    // masks to check for errors
     PRN_STATUS_MASK_ERRORS = 0x7F0,
     PRN_STATUS_MASK_ANY    = 0x7FF,
 };

src/maps.c

 
 void map_title(void) NONBANKED {
     START_ROM_BANK(BANK(title_map)) {
-
         set_bkg_palette(OAMF_CGB_PAL0, title_map_PALETTE_COUNT, title_map_palettes);
         set_bkg_data(0, title_map_TILE_COUNT, title_map_tiles);
 
                       title_map_WIDTH / title_map_TILE_W,
                       title_map_HEIGHT / title_map_TILE_H,
                       title_map_map);
-
     } END_ROM_BANK
 
     move_bkg(0, 0);

src/sound_menu.c

     END
 };
 
+#define DRUM_LOOP \
+    dSI, dSI, dSn, dSI, dKi, dSI, dSI, dSI, \
+    dSn, dSI, dSI, dSI, dKi, dSI, dSI, dSI  \
+
+const enum drums menu_drums[] = {
+    // intro
+
+    DRUM_LOOP,
+    DRUM_LOOP,
+
+    DRUM_LOOP,
+    DRUM_LOOP,
+
+    // repeat 1
+
+    DRUM_LOOP,
+    DRUM_LOOP,
+
+    DRUM_LOOP,
+    DRUM_LOOP,
+
+    DRUM_LOOP,
+    DRUM_LOOP,
+
+    DRUM_LOOP,
+    DRUM_LOOP,
+
+    // bridge
+
+    DRUM_LOOP,
+    DRUM_LOOP,
+
+    DRUM_LOOP,
+    DRUM_LOOP,
+
+    // repeat 2
+
+    DRUM_LOOP,
+    DRUM_LOOP,
+
+    DRUM_LOOP,
+    DRUM_LOOP,
+
+    // bridge
+
+    DRUM_LOOP,
+    DRUM_LOOP,
+
+    DRUM_LOOP,
+    DRUM_LOOP,
+
+    // end
+
+    dSI, dSI, dSI, dSI, dSI, dSI, dSI, dSI,
+    dSI, dSI, dSI, dSI, dSI, dSI, dSI, dSI,
+    dSI, dSI, dSI, dSI, dSI, dSI, dSI, dSI,
+
+    dSI, dSI, dSI, dSI, dSI, dSI, dSI, dSI,
+    dSI, dSI, dSI, dSI, dSI, dSI, dSI, dSI,
+    dEND
+};
+
 const struct music music_menu = {
     .notes = menu_music,
     .notes2 = menu_music2,
-    .drums = NULL,
+    .drums = menu_drums,
     .duration = 150,
     .repeat = 0,
 };

src/sound_over.c

 
 #define DRUM_LOOP \
     dKi, dSI, dSI, dSI, dSI, dSI, dKi, dSI, \
-    dSn, dSI, dSI, dSI, dKi, dSI, dSI, dSI \
+    dSn, dSI, dSI, dSI, dKi, dSI, dSI, dSI  \
 
 const enum drums over_drums[] = {
     DRUM_LOOP,