Mega65 keyboard support improvements

c64/aliases/,aliases_hardware.s

@@ -70,6 +70,13 @@
 	.label VIC_XSCAN    = $D02F // C128 only
 	.label VIC_CLKRATE  = $D030 // C128 only
 
+#endif
+
+#if CONFIG_MB_MEGA_65
+
+	.label VIC_KEY      = $D02F
+	.label VIC_XPOS     = $D050
+
 #endif
 
 	// SID registers
@@ -165,7 +172,7 @@
 	.const BIT_CIA2_PRA_CLK_IN   = $40  // 0 - low (pulled), 1 - high (released)
 	.const BIT_CIA2_PRA_DAT_IN   = $80  // 0 - low (pulled), 1 - high (released)
 
-#if CONFIG_MB_MEGA_65 
+#if CONFIG_MB_MEGA_65
 
 	.const C65_EXTKEYS_PR  = $D607
 	.const C65_EXTKEYS_DDR = $D608

c64/kernal/keyboard/scnkey.s

@@ -30,6 +30,34 @@
 
 SCNKEY:
 
+#if CONFIG_KEYBOARD_C65 && CONFIG_MB_MEGA_65
+
+	// Idea by Paul Gardner-Stephen
+
+	lda VIC_XPOS                       // check raster X position
+	cmp VIC_XPOS                       // if it changes, we are on a MEGA65 with VIC-IV registers already visible
+	bne scnkey_viciv_mode
+
+	// We are on machine that is not in VIC-IV IO mode, so try enabling it (harmless on C64/C65)
+	// If we are on a C65 (or MEGA65 with C65 VIC-III IO mode selected), the above test would
+	// have failed, but we could already be in C65 IO mode. In that case, this will disable C65 IO
+	// mode when done. This is not ideal, but as MEGA65s start C65 mode with VIC-IV IO mode
+	// selected anyway, it should not be a big problem in practice.
+
+	lda #$A5
+	sta VIC_KEY
+	lda #$96
+	sta VIC_KEY
+
+	jsr scnkey_viciv_mode
+
+	sta VIC_KEY
+	rts
+
+scnkey_viciv_mode:
+
+#endif
+
 	// Prepare for SHFLAG update
 
 	lda SHFLAG