flash rom command parsing

src/hw/rom/boot.c

@@ -22,10 +22,9 @@ static void boot_rom_write(struct boot *boot, uint32_t addr, uint32_t data,
   LOG_FATAL("Can't write to boot rom");
 }
 
-static int boot_load(struct boot *boot, const char *path) {
+static int boot_load_rom(struct boot *boot, const char *path) {
   FILE *fp = fopen(path, "rb");
   if (!fp) {
-    LOG_WARNING("Failed to open boot at \"%s\"", path);
     return 0;
   }
 
@@ -34,26 +33,23 @@ static int boot_load(struct boot *boot, const char *path) {
   fseek(fp, 0, SEEK_SET);
 
   if (size != BIOS_SIZE) {
-    LOG_WARNING("BIOS size mismatch, is %d, expected %d", size, BIOS_SIZE);
+    LOG_WARNING("Boot rom size mismatch, is %d, expected %d", size, BIOS_SIZE);
     fclose(fp);
     return 0;
   }
 
   int n = (int)fread(boot->rom, sizeof(uint8_t), size, fp);
+  CHECK_EQ(n, size);
   fclose(fp);
 
-  if (n != size) {
-    LOG_WARNING("BIOS read failed");
-    return 0;
-  }
-
   return 1;
 }
 
 static bool boot_init(struct device *dev) {
   struct boot *boot = (struct boot *)dev;
 
-  if (!boot_load(boot, OPTION_bios)) {
+  if (!boot_load_rom(boot, OPTION_bios)) {
+    LOG_WARNING("Failed to load boot rom");
     return false;
   }
 

src/hw/rom/flash.c

@@ -2,33 +2,38 @@
 #include "hw/rom/flash.h"
 #include "core/option.h"
 #include "hw/dreamcast.h"
+#include "sys/filesystem.h"
 
 DEFINE_OPTION_STRING(flash, "dc_flash.bin", "Path to flash ROM");
 
-// there doesn't seem to exist any documentation on the actual flashrom used
-// by the dreamcast, however, there are several people who have replaced it
-// with the MX29LV160 successfully
+// there doesn't seem to be any documentation on the flash rom used by thae
+// dreamcast. however, several people have replaced it with the MX29LV160TMC-90
+// successfully. the implementation of the command parsing here is based on its
+// datasheet. note, the dreamcast seems to only use the word mode command
+// sequences, so that is all that is implemented
+
 #define FLASH_SIZE 0x00020000
+#define SECTOR_SIZE 0x4000
+#define CMD_NONE 0x0
+#define CMD_ERASE 0x80
+#define CMD_ERASE_CHIP 0x10
+#define CMD_ERASE_SECTOR 0x30
+#define CMD_PROGRAM 0xa0
 
 struct flash {
   struct device;
+  // path to persistent flash rom kept in the application directory
+  char app_path[PATH_MAX];
+  // cmd parsing state
+  int cmd;
+  int cmd_state;
+  // rom data
   uint8_t rom[FLASH_SIZE];
 };
 
-static uint32_t flash_rom_read(struct flash *flash, uint32_t addr,
-                               uint32_t data_mask) {
-  return READ_DATA(&flash->rom[addr]);
-}
-
-static void flash_rom_write(struct flash *flash, uint32_t addr, uint32_t data,
-                            uint32_t data_mask) {
-  WRITE_DATA(&flash->rom[addr]);
-}
-
-static int flash_load(struct flash *flash, const char *path) {
+static int flash_load_rom(struct flash *flash, const char *path) {
   FILE *fp = fopen(path, "rb");
   if (!fp) {
-    LOG_WARNING("Failed to open flash at \"%s\"", path);
     return 0;
   }
 
@@ -43,20 +48,119 @@ static int flash_load(struct flash *flash, const char *path) {
   }
 
   int n = (int)fread(flash->rom, sizeof(uint8_t), size, fp);
+  CHECK_EQ(n, size);
   fclose(fp);
 
-  if (n != size) {
-    LOG_WARNING("Flash read failed");
+  return 1;
+}
+
+static int flash_save_rom(struct flash *flash, const char *path) {
+  FILE *fp = fopen(path, "wb");
+  if (!fp) {
     return 0;
   }
 
+  int n = (int)fwrite(flash->rom, 1, FLASH_SIZE, fp);
+  CHECK_EQ(n, FLASH_SIZE);
+  fclose(fp);
+
   return 1;
 }
 
+static uint32_t flash_cmd_read(struct flash *flash, uint32_t addr, uint32_t data_mask) {
+  uint32_t *mem = (uint32_t *)&flash->rom[addr];
+  return *mem & data_mask;
+}
+
+static void flash_cmd_program(struct flash *flash, uint32_t addr, uint32_t data,
+                              uint32_t data_mask) {
+  uint32_t *mem = (uint32_t *)&flash->rom[addr];
+  *mem &= ~data_mask | data;
+
+  // update persistent copy of the flash rom
+  CHECK(flash_save_rom(flash, flash->app_path));
+}
+
+static void flash_cmd_erase_chip(struct flash *flash) {
+  memset(flash->rom, 0xff, FLASH_SIZE);
+}
+
+static void flash_cmd_erase_sector(struct flash *flash, uint32_t addr) {
+  addr &= ~(SECTOR_SIZE - 1);
+  memset(&flash->rom[addr], 0xff, SECTOR_SIZE);
+}
+
+static uint32_t flash_read(struct flash *flash, uint32_t addr,
+                           uint32_t data_mask) {
+  CHECK_EQ(flash->cmd_state, 0);
+  return flash_cmd_read(flash, addr, data_mask);
+}
+
+static void flash_write(struct flash *flash, uint32_t addr, uint32_t data,
+                        uint32_t data_mask) {
+  switch (flash->cmd_state) {
+    case 0: {
+      CHECK(addr == 0x5555 && data == 0xaa);
+      flash->cmd_state++;
+    } break;
+
+    case 1: {
+      CHECK(addr == 0x2aaa && data == 0x55);
+      flash->cmd_state++;
+    } break;
+
+    case 2: {
+      CHECK(addr == 0x5555 && (data == CMD_ERASE || data == CMD_PROGRAM));
+      flash->cmd = data;
+      flash->cmd_state++;
+    } break;
+
+    case 3: {
+      if (flash->cmd == CMD_PROGRAM) {
+        flash_cmd_program(flash, addr, data, data_mask);
+        flash->cmd_state = 0;
+      } else {
+        CHECK_EQ(flash->cmd, CMD_ERASE);
+        CHECK(addr == 0x5555 && data == 0xaa);
+        flash->cmd_state++;
+      }
+    } break;
+
+    case 4: {
+      CHECK(addr == 0x2aaa && data == 0x55);
+      flash->cmd_state++;
+    } break;
+
+    case 5: {
+      if (data == CMD_ERASE_CHIP) {
+        CHECK(addr == 0x5555);
+        flash_cmd_erase_chip(flash);
+      } else {
+        CHECK_EQ(data, CMD_ERASE_SECTOR);
+        flash_cmd_erase_sector(flash, addr);
+      }
+      flash->cmd_state = 0;
+    } break;
+
+    default:
+      LOG_FATAL("Unexpected flash command state %d", flash->cmd_state);
+      break;
+  }
+}
+
 static bool flash_init(struct device *dev) {
   struct flash *flash = (struct flash *)dev;
 
-  if (!flash_load(flash, OPTION_flash)) {
+  // keep a persistent copy of the flash rom in the application directory
+  const char *appdir = fs_appdir();
+  snprintf(flash->app_path, sizeof(flash->app_path),
+           "%s" PATH_SEPARATOR "flash.bin", appdir);
+
+  // attempt to load flash rom from the application directory first, falling
+  // back to the command line path if it doesn't exist
+  if (!(flash_load_rom(flash, flash->app_path) ||
+        flash_load_rom(flash, OPTION_flash))) {
+    LOG_WARNING("Failed to load flash rom");
     return false;
   }
 
@@ -76,7 +180,7 @@ void flash_destroy(struct flash *flash) {
 // clang-format off
 AM_BEGIN(struct flash, flash_rom_map);
   AM_RANGE(0x00000000, 0x0001ffff) AM_HANDLE("flash rom",
-                                             (mmio_read_cb)&flash_rom_read,
-                                             (mmio_write_cb)&flash_rom_write)
+                                             (mmio_read_cb)&flash_read,
+                                             (mmio_write_cb)&flash_write)
 AM_END();
 // clang-format on

src/hw/sh4/sh4.c

@@ -803,7 +803,7 @@ REG_R32(sh4_cb, PDTRA) {
   // 3. When VREG1 = 1 and VREG0 = 1 are written in the AICA register,
   // VIDEO1 = 0 and VIDEO0 = 0 are output.  VIDEO0 is connected to the
   // DVE-DACH pin, and handles switching between RGB and NTSC/PAL.
-  // v |= 0x3 << 8;
+  v |= 0x3 << 8;
   return v;
 }