diff --git a/src/mame/drivers/namcos22.c b/src/mame/drivers/namcos22.c
index c8559906e85..f8b3ca7c61c 100644
--- a/src/mame/drivers/namcos22.c
+++ b/src/mame/drivers/namcos22.c
@@ -1463,7 +1463,8 @@ static READ16_HANDLER( pdp_begin_r )
 				}
 				break;
 
-			case 0xfffd: /* unknown */
+			case 0xfffd: /* direct command to render device */
+				// len -> command (eg. BB0003) -> data
 				numWords = ReadFromCommRAM(state, offs++);
 				while( numWords-- )
 				{
@@ -1473,7 +1474,7 @@ static READ16_HANDLER( pdp_begin_r )
 				break;
 
 			case 0xfffe: /* unknown */
-				data = ReadFromCommRAM(state, offs++); /* ??? */
+				data = ReadFromCommRAM(state, offs++); /* ??? (usually 0x400 or 0) */
 				break;
 
 			case 0xffff: /* "goto" command */
@@ -5742,7 +5743,7 @@ GAME( 1994, alpinerd, 0,         namcos22s, alpiner,  alpiner,  ROT0, "Namco", "
 GAME( 1994, alpinerc, alpinerd,  namcos22s, alpiner,  alpiner,  ROT0, "Namco", "Alpine Racer (Rev. AR2 Ver.C)"             , GAME_IMPERFECT_SOUND|GAME_IMPERFECT_GRAPHICS )
 GAME( 1995, airco22b, 0,         namcos22s, airco22,  airco22,  ROT0, "Namco", "Air Combat 22 (Rev. ACS1 Ver.B, Japan)"    , GAME_IMPERFECT_SOUND|GAME_IMPERFECT_GRAPHICS|GAME_NOT_WORKING ) // boots but missing sprite clear DMA?
 GAME( 1995, cybrcycc, 0,         namcos22s, cybrcycc, cybrcyc,  ROT0, "Namco", "Cyber Cycles (Rev. CB2 Ver.C)"             , GAME_IMPERFECT_SOUND|GAME_IMPERFECT_GRAPHICS ) // 95/04/04
-GAME( 1995, dirtdash, 0,         namcos22s, dirtdash, dirtdash, ROT0, "Namco", "Dirt Dash (Rev. DT2)"                      , GAME_IMPERFECT_SOUND|GAME_IMPERFECT_GRAPHICS|GAME_NOT_WORKING ) // 95/12/20 20:01:56. locks up, slave dsp?
+GAME( 1995, dirtdash, 0,         namcos22s, dirtdash, dirtdash, ROT0, "Namco", "Dirt Dash (Rev. DT2)"                      , GAME_IMPERFECT_SOUND|GAME_IMPERFECT_GRAPHICS|GAME_NOT_WORKING ) // 95/12/20 20:01:56. locks up, dsp comms/slave dsp? - romdump looks fine
 GAME( 1995, timecris, 0,         namcos22s, timecris, timecris, ROT0, "Namco", "Time Crisis (Rev. TS2 Ver.B)"              , GAME_IMPERFECT_SOUND|GAME_IMPERFECT_GRAPHICS ) // 96/04/02 18:48:00
 GAME( 1995, timecrisa,timecris,  namcos22s, timecris, timecris, ROT0, "Namco", "Time Crisis (Rev. TS2 Ver.A)"              , GAME_IMPERFECT_SOUND|GAME_IMPERFECT_GRAPHICS ) // 96/01/08 18:56:09
 GAME( 1996, propcycl, 0,         namcos22s, propcycl, propcycl, ROT0, "Namco", "Prop Cycle (Rev. PR2 Ver.A)"               , GAME_IMPERFECT_SOUND|GAME_IMPERFECT_GRAPHICS ) // 96/06/18 21:22:13