add infos to the 1943 driver (video) about priorities encoded in PROM

src/mame/video/1943.c

@@ -1,3 +1,32 @@
+/***************************************************************************
+
+1943 Video Hardware
+
+This board handles tile/tile and tile/sprite priority with a PROM. Its
+working is hardcoded in the driver.
+
+The PROM have address inputs wired as follows:
+
+A0 bg (SCR) opaque
+A1 bit 2 of sprite (OBJ) attribute (guess)
+A2 bit 3 of sprite (OBJ) attribute (guess)
+A3 sprite (OBJ) opaque
+A4 fg (CHAR) opaque
+A5 wired to mass
+A6 wired to mass
+A7 wired to mass
+
+2 bits of the output selects the active layer, it can be:
+(output & 0x03)
+0 bg2 (SCR2)
+1 bg (SCR)
+2 sprite (OBJ)
+3 fg (CHAR)
+
+other 2 bits (output & 0x0c) unknown
+
+***************************************************************************/
+
 #include "driver.h"
 
 UINT8 *c1943_scrollx;