Copy reset stack and program counter from ROM to RAM

Copy the reset supervisor stack pointer and reset program counter from
ROM to RAM to emulate the ROM overlay during processor reset.

Author: frno7

include/atari/rom.h

@@ -8,7 +8,6 @@
 
 #include "atari/device.h"
 
-extern const struct device rom0_device;
-extern const struct device rom1_device;
+extern const struct device rom_device;
 
 #endif /* ATARI_ROM_H */

lib/atari/Makefile

@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0
 
-lib/atari/rom.c: $(LIBPSGPLAY_TOS_HEADER)
+lib/atari/ram.c lib/atari/rom.c: $(LIBPSGPLAY_TOS_HEADER)
 
 ATARI_SRC := $(addprefix lib/atari/,					\
 	bus.c								\

lib/atari/device.c

@@ -25,8 +25,7 @@ static struct machine_device {
 	u64 machine_cycle_event;
 	const struct device *device;
 } list[] = {
-	{ .device = &rom0_device    },
-	{ .device = &rom1_device    },
+	{ .device = &rom_device     },
 	{ .device = &glue_device    },
 	{ .device = &ram_device     },
 	{ .device = &mfp_device     },

lib/atari/mmu.c

@@ -38,8 +38,7 @@ static void mmu_bus_wait(const struct device *dev)
 	valid_device_bus_address(bus_address, dev) ? dev
 #define DMA_DEVICES(bus_address)					\
 	DMA_DEVICE(bus_address, &ram_device) :				\
-	DMA_DEVICE(bus_address, &rom0_device) :				\
-	DMA_DEVICE(bus_address, &rom1_device) : NULL
+	DMA_DEVICE(bus_address, &rom_device) : NULL
 
 u8 dma_read_memory_8(u32 bus_address)
 {

lib/atari/ram.c

@@ -12,11 +12,14 @@
 #include "atari/sound.h"
 #include "atari/system-variable.h"
 
+#include "tos/tos.h"
+
 static u8 ram[4 * 1024 * 1024];	/* 4 MiB of RAM */
 
 static void ram_reset(const struct device *device)
 {
-	memset(ram, 0, sizeof(ram));
+	memcpy(&ram[0], tos, 8);	/* ROM overlay during reset */
+	memset(&ram[8], 0, sizeof(ram) - 8);
 }
 
 static u8 ram_rd_u8(const struct device *device, u32 dev_address)

lib/atari/rom.c

@@ -20,19 +20,7 @@ static u16 rom_rd_u16(const struct device *device, u32 dev_address)
 		(tos[dev_address] << 8) | tos[dev_address + 1] : 0;
 }
 
-const struct device rom0_device = {
-	.name = "rom",
-	.bus = {
-		.address = 0,
-		.size = 8,
-	},
-	.rd_u8  = rom_rd_u8,
-	.rd_u16 = rom_rd_u16,
-	.wr_u8  = bus_error_wr_u8,
-	.wr_u16 = bus_error_wr_u16,
-};
-
-const struct device rom1_device = {
+const struct device rom_device = {
 	.name = "rom",
 	.frequency = 8000000,
 	.bus = {