DEBUG: Do not clear cycle count when entering the debugger, doing so …

…jumps emulator time forward up to 1ms. Add VRT command for programmers who wish to see the output of their program while debugging [#4980]

CHANGELOG

@@ -1,4 +1,12 @@
 Next:
+  - Fixed debugger mapper shortcut bug where entering the debugger
+    completes the 1 ms "tick" early, effectively jumping emulator time
+    up to start of the next ms. This might explain the mysterious cases
+    where a program always fails to work unless you are debugging it.
+    (joncampbell123).
+  - Added debugger command "VRT" which resumes running the guest until
+    vertical retrace. Added for programmers who wish to write something
+    to screen and then see it show up. (joncampbell123).
   - Fix IMGMOUNT, when mounting FAT disk images, to provide the DPB the
     actual media id byte instead of assuming 0xF8 or 0xF0. INT AH=1Ch
     should now report the proper media id byte for any floppy format,

src/debug/debug.cpp

@@ -76,6 +76,8 @@ char *FormatDate(uint16_t year, uint8_t month, uint8_t day);
 void GFX_SetTitle(int32_t cycles, int frameskip, Bits timing, bool paused);
 bool pc98_pegc_linear_framebuffer_enabled(void);
 
+bool DEBUG_HaltOnRetrace = false;
+
 extern bool                 dos_kernel_disabled;
 extern bool                 is_paused;
 extern bool                 pc98_crt_mode;
@@ -2228,6 +2230,11 @@ bool ParseCommand(char* str) {
 		return true;
 	}
 
+	if (command == "VRT") {
+		DEBUG_HaltOnRetrace = true;
+		command = "RUN";
+	}
+
 	if (command == "RUN") {
 		DrawRegistersUpdateOld();
 		debug_running = false;
@@ -3610,7 +3617,7 @@ bool ParseCommand(char* str) {
 		DEBUG_ShowMsg("SR [reg] [value]          - Set register value. Multiple pairs allowed.\n");
 		DEBUG_ShowMsg("SM [seg]:[off] [val] [.]..- Set memory with following values.\n");
 		DEBUG_ShowMsg("SMV [addr] [val] [.]..    - Set memory with following values at linear (virtual) address.\n");
-        DEBUG_ShowMsg("FM [seg]:[off]            - Freeze memory value at address.\n");
+		DEBUG_ShowMsg("FM [seg]:[off]            - Freeze memory value at address.\n");
 		DEBUG_ShowMsg("EV [value [value] ...]    - Show register value(s).\n");
 		DEBUG_ShowMsg("IV [seg]:[off] [name]     - Create var name for memory address.\n");
 		DEBUG_ShowMsg("SV [filename]             - Save var list in file.\n");
@@ -3641,6 +3648,7 @@ bool ParseCommand(char* str) {
 		DEBUG_ShowMsg("TIMERIRQ                  - Run the system timer.\n");
 		DEBUG_ShowMsg("TIME [time]               - Display or change the internal time.\n");
 		DEBUG_ShowMsg("DATE [date]               - Display or change the internal date.\n");
+		DEBUG_ShowMsg("VRT                       - Run, then enter debugger at next vertical retrace.\n");
 
 		DEBUG_ShowMsg("IN[P|W|D] [port]          - I/O port read byte/word/dword.\n");
 		DEBUG_ShowMsg("OUT[P|W|D] [port] [data]  - I/O port write byte/word/dword.\n");
@@ -5157,7 +5165,8 @@ Bitu DEBUG_EnableDebugger(void)
 	if (!debugging || (debugging && debug_running))
 		DEBUG_Enable_Handler(true);
 
-	CPU_Cycles=CPU_CycleLeft=0;
+	CPU_CycleLeft += CPU_Cycles;
+	CPU_Cycles = 0;
 	return 0;
 }
 

src/hardware/vga_draw.cpp

@@ -5654,9 +5654,21 @@ pic_tickindex_t VGA_PITSync_delay(void) {
 	return et;
 }
 
+#if C_DEBUG
+extern bool DEBUG_HaltOnRetrace;
+Bitu DEBUG_EnableDebugger(void);
+#endif
+
 static void VGA_VerticalTimer(Bitu /*val*/) {
 	double current_time = PIC_GetCurrentEventTime();
 
+#if C_DEBUG
+	if (DEBUG_HaltOnRetrace) {
+		DEBUG_EnableDebugger();
+		DEBUG_HaltOnRetrace = false;
+	}
+#endif
+
 	dbg_event_maxscan = false;
 	dbg_event_scanstep = false;
 	dbg_event_hretrace = false;