MEGA65: "read of unwritten memory" debug mode #405

Rhialto had the feature request to have a mode, where Xemu/MEGA65 can warn you
on reading memory which was not written before, can be useful to find ROM bugs.

In this current form, it's quite minimal and simple:

1. Only works on the first 126K of physical RAM
2. Only works from command line, start emulation with paramter: -ramcheckread
3. You need to watch the output of the emulator, so on UNIX-like/Linux/Mac systems,
   emulator should be started from terminal window, on Windows, Xemu
   console must be open (start also with parameter: -syscon)
4. Check the output of the emulator, you can find lines like:
   MEM: DEBUG: main RAM at linear address $101A0 has been read without prior write; PC=$8613 [$20613]
   The PC value can be off by some bytes, because it may have been
   incremented already during opcode emulation. The [...] is the linear
   address for the mentioned CPU PC value.

Well, that's it.

targets/mega65/configdb.c

@@ -112,6 +112,7 @@ static const struct xemutools_configdef_switch_st switch_options[] = {
 	{ "fastboot", "Try to use sleepless emulation mode during booting", &configdb.fastboot },
 	{ "matrixstart", "Start with matrix-mode activated", &configdb.matrixstart },
 	{ "matrixdisable", "Disable the matrix hotkey", &configdb.matrixdisable },
+	{ "ramcheckread", "Enabled warnings on reading unwritten memory (first 126K only)", &configdb.ramcheckread },
 	{ NULL }
 };
 
@@ -152,7 +153,7 @@ static const void *do_not_save_opts[] = {
 	&configdb.matrixstart,
 	&configdb.dumpmem, &configdb.dumpscreen, &configdb.screenshot_and_exit,
 	&configdb.testing, &configdb.hyperdebug, &configdb.hyperdebugfreezer, &configdb.usestubrom, &configdb.useinitrom, &configdb.useutilmenu,
-	&configdb.cartbin8000, &configdb.winpos,
+	&configdb.cartbin8000, &configdb.winpos, &configdb.ramcheckread,
 	NULL
 };
 

targets/mega65/configdb.h

@@ -112,6 +112,7 @@ struct configdb_st {
 	int	matrixstart;
 	int	matrixdisable;
 	char	*winpos;
+	int	ramcheckread;
 };
 
 extern struct configdb_st configdb;

targets/mega65/hypervisor.c

@@ -269,6 +269,7 @@ void hypervisor_start_machine ( void )
 	extract_version_string(hyppo_version_string, sizeof hyppo_version_string);
 	DEBUGPRINT("HYPERVISOR: HYPPO version \"%s\" (%s) starting with TRAP reset (#$%02X)" NL, hyppo_version_string, hickup_is_overriden ? "OVERRIDEN" : "built-in", TRAP_RESET);
 	hypervisor_enter(TRAP_RESET);
+	memory_reset_unwritten_debug_stat();
 }
 
 
@@ -299,6 +300,7 @@ static inline void first_leave ( void )
 	hdos_notify_system_start_end();
 	xemu_sleepless_temporary_mode(0);	// turn off temporary sleepless mode which may have been enabled before
 	vic_frame_counter_since_boot = 0;
+	//memory_reset_unwritten_debug_stat();	// FIXME/TODO: commented out since it generates a **tons** of warnings then with the "unwritten mem read" debug mode (-ramcheckread emu option)
 	DEBUGPRINT("HYPERVISOR: first return after RESET, end of processing workarounds." NL);
 }
 

targets/mega65/memory_mapper.c

@@ -48,6 +48,7 @@ Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */
 
 // 512K is the max "main" RAM. Currently only 384K is used by M65. We want to make sure, the _total_ size is power of 2, so we can protect accesses with simple bit masks as a last-resort-protection
 Uint8 main_ram[512 << 10];
+static Uint8 main_ram_written[0x1F800U];
 // 32K of colour RAM. VIC-IV can see this as for colour information only. The first 2K can be seen at the last 2K of
 // the chip-RAM. Also, the first 1 or 2K can be seen in the C64-style I/O area too, at $D800
 Uint8 colour_ram[0x8000];
@@ -162,12 +163,38 @@ static Uint32 policy4k[0x10];		// memory policy with MAP taken account (the real
 static Uint8 zero_page_reader ( const Uint32 addr32 );
 static void  zero_page_writer ( const Uint32 addr32, const Uint8 data );
 
+
+static void checked_reader_warning ( const Uint32 addr32 )
+{
+	DEBUGPRINT("MEM: DEBUG: main RAM at linear address $%X has been read without prior write; PC=$%04X [$%X]" NL, addr32, cpu65.pc, memory_cpu_addr_to_linear(cpu65.pc, NULL));
+}
+
+
+static Uint8 zero_page_checked_reader ( const Uint32 addr32 ) {
+	if (!main_ram_written[addr32])
+		checked_reader_warning(addr32);
+	return zero_page_reader(addr32);
+}
+static void  zero_page_checked_writer ( const Uint32 addr32, const Uint8 data ) {
+	main_ram_written[addr32] = 1;
+	zero_page_writer(addr32, data);
+}
+
 static Uint8 main_ram_reader ( const Uint32 addr32 ) {
 	return main_ram[addr32];
 }
 static void  main_ram_writer ( const Uint32 addr32, const Uint8 data ) {
 	main_ram[addr32] = data;
 }
+static Uint8 main_ram_checked_reader ( const Uint32 addr32 ) {
+	if (!main_ram_written[addr32])
+		checked_reader_warning(addr32);
+	return main_ram[addr32];
+}
+static void  main_ram_checked_writer ( const Uint32 addr32, const Uint8 data ) {
+	main_ram_written[addr32] = 1;
+	main_ram[addr32] = data;
+}
 static void  shared_main_ram_writer ( const Uint32 addr32, const Uint8 data ) {
 	main_ram[addr32] = data;
 	colour_ram[addr32 - 0x1F800U] = data;
@@ -348,6 +375,30 @@ static struct mem_map_st mem_map[] = {
 
 static XEMU_INLINE void slot_assignment_postprocessing ( const Uint32 slot )
 {
+	if (XEMU_UNLIKELY(configdb.ramcheckread && mem_slot_rd_addr32[slot] < 0x1F800U)) {
+		if (mem_slot_rd_func[slot] == main_ram_reader) {
+#ifdef			MEM_USE_DATA_POINTERS
+			mem_slot_rd_data[slot] = NULL;
+#endif
+			mem_slot_rd_func[slot] = main_ram_checked_reader;
+		} else if (mem_slot_rd_func[slot] == zero_page_reader) {
+#ifdef			MEM_USE_DATA_POINTERS
+			mem_slot_rd_data[slot] = NULL;
+#endif
+			mem_slot_rd_func[slot] = zero_page_checked_reader;
+		}
+		if (mem_slot_wr_func[slot] == main_ram_writer) {
+#ifdef			MEM_USE_DATA_POINTERS
+			mem_slot_wr_data[slot] = NULL;
+#endif
+			mem_slot_wr_func[slot] = main_ram_checked_writer;
+		} else if (mem_slot_wr_func[slot] == zero_page_writer) {
+#ifdef			MEM_USE_DATA_POINTERS
+			mem_slot_wr_data[slot] = NULL;
+#endif
+			mem_slot_wr_func[slot] = zero_page_checked_writer;
+		}
+	}
 	mem_slot_rd_func_real[slot] = mem_slot_rd_func[slot];
 	mem_slot_wr_func_real[slot] = mem_slot_wr_func[slot];
 #ifdef	MEM_WATCH_SUPPORT
@@ -934,6 +985,7 @@ void memory_init (void )
 	// Initiailize memory content with something ...
 	// NOTE: make sure the first 2K of colour_ram is the **SAME** as the 2K part of main_ram at offset $1F800
 	memset(main_ram,   0x00, sizeof main_ram);
+	memory_reset_unwritten_debug_stat();
 	memset(colour_ram, 0x00, sizeof colour_ram);
 	memset(attic_ram,  0xFF, sizeof attic_ram);
 	DEBUGPRINT("MEM: memory decoder initialized, %uK fast, %uK attic, %uK colour, %uK font RAM" NL,
@@ -945,6 +997,12 @@ void memory_init (void )
 }
 
 
+void memory_reset_unwritten_debug_stat ( void )
+{
+	memset(main_ram_written, 0x00, sizeof main_ram_written);
+}
+
+
 // Warning: this overwrites ref_slot!
 static XEMU_INLINE Uint32 cpu_get_flat_addressing_mode_address ( const Uint8 index )
 {

targets/mega65/memory_mapper.h

@@ -20,6 +20,7 @@ Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */
 #define XEMU_MEGA65_MEMORY_MAPPER_H_INCLUDED
 
 extern void memory_init ( void );
+extern void memory_reset_unwritten_debug_stat ( void );
 extern void memory_set_rom_protection ( const bool protect );
 extern void memory_reconfigure (
 	const Uint8 d030_value, const Uint8 new_io_mode, const Uint8 new_cpu_port0, const Uint8 new_cpu_port1,