# HG changeset patch
# User Michael Pavone <pavone@retrodev.com>
# Date 1661226199 25200
# Node ID 2f8984ff5c854056cfcd691b5a797bf88fdcf5fd
# Parent  f11f4399d64bb444a9f80ec9449dde79f565d1e6
Prevent Mode 5 selection when not emulating the Genesis VDP

diff -r f11f4399d64b -r 2f8984ff5c85 vdp.c
--- a/vdp.c	Mon Aug 22 20:19:59 2022 -0700
+++ b/vdp.c	Mon Aug 22 20:43:19 2022 -0700
@@ -3822,9 +3822,12 @@
 				//printf("register %d set to %X\n", reg, value & 0xFF);
 				if (reg == REG_MODE_1 && (value & BIT_HVC_LATCH) && !(context->regs[reg] & BIT_HVC_LATCH)) {
 					vdp_latch_hv(context);
-				}
-				if (reg == REG_BG_COLOR) {
+				} else if (reg == REG_BG_COLOR) {
 					value &= 0x3F;
+				} else if (reg == REG_MODE_2 && context->type != VDP_GENESIS) {
+					// only the Genesis VDP does anything with this bit
+					// so just clear it to prevent Mode 5 selection if we're not emulating that chip
+					value &= ~BIT_MODE_5;
 				}
 				/*if (reg == REG_MODE_4 && ((value ^ context->regs[reg]) & BIT_H40)) {
 					printf("Mode changed from H%d to H%d @ %d, frame: %d\n", context->regs[reg] & BIT_H40 ? 40 : 32, value & BIT_H40 ? 40 : 32, context->cycles, context->frame);