Split bus functionality

1 files changed, 206 insertions, 0 deletions

diff --git a/bus.c b/bus.c
new file mode 100644
index 0000000..9e23586
--- /dev/null
+++ b/bus.c
@@ -0,0 +1,206 @@
+#include "bus.h"
+
+#include <assert.h>
+#include <stdarg.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+
+#include "musashi-m68k/m68k.h"
+
+unsigned char g_rom[ROM_SIZE] = {0};
+unsigned char g_ram[RAM_SIZE] = {0};
+unsigned char g_io1[IO1_SIZE] = {0};
+unsigned char g_io2[IO2_SIZE] = {0};
+
+static void exit_error(char* fmt, ...)
+{
+    va_list args;
+    va_start(args, fmt);
+    vfprintf(stderr, fmt, args);
+    va_end(args);
+    fprintf(stderr, "\n");
+    unsigned int pc = m68k_get_reg(NULL, M68K_REG_PPC);
+    char buff[100];
+    m68k_disassemble(buff, pc, M68K_CPU_TYPE_68000);
+    fprintf(stderr, "%08x: %s\n", pc, buff);
+    exit(EXIT_FAILURE);
+}
+
+static inline bool is_in_range(uint32_t value, uint32_t begin, uint32_t length)
+{
+    return value >= begin && value <= begin + length;
+}
+
+enum bitness {
+    BITNESS_8,
+    BITNESS_16,
+    BITNESS_32,
+};
+
+struct read_result {
+    unsigned int result;
+    bool successful;
+};
+
+static inline unsigned int memory_read_concrete(
+        enum bitness bitness,
+        unsigned char const * base,
+        unsigned int address)
+{
+    switch (bitness) {
+    case BITNESS_8:
+        return base[address];
+    case BITNESS_16:
+        return (base[address] << 8) | base[address + 1];
+    case BITNESS_32:
+        return (base[address] << 24) |
+            (base[address + 1] << 16) |
+            (base[address + 2] << 8) |
+            base[address + 3];
+    }
+    __builtin_unreachable();
+}
+
+static inline struct read_result memory_read(
+        enum bitness bitness,
+        unsigned int address)
+{
+    if (is_in_range(address, ROM_START, ROM_SIZE))
+        return (struct read_result){
+            memory_read_concrete(bitness, g_rom, address - ROM_START),
+            true,
+        };
+    else if (is_in_range(address, RAM_START, RAM_SIZE))
+        return (struct read_result){
+            memory_read_concrete(bitness, g_ram, address - RAM_START),
+            true,
+        };
+    else if (is_in_range(address, IO1_START, IO1_SIZE))
+        return (struct read_result){
+            memory_read_concrete(bitness, g_io1, address - IO1_START),
+            true,
+        };
+    else if (is_in_range(address, IO2_START, IO2_SIZE))
+        return (struct read_result){
+            memory_read_concrete(bitness, g_io2, address - IO2_START),
+            true,
+        };
+    return (struct read_result){0, false};
+}
+
+static inline void memory_write_concrete(
+        enum bitness bitness,
+        unsigned char * base,
+        unsigned int address,
+        unsigned int value)
+{
+    switch (bitness) {
+    case BITNESS_8:
+        base[address] = value & 0xff;
+        break;
+    case BITNESS_16:
+        base[address + 0] = (value >> 8) & 0xff;
+        base[address + 1] = value & 0xff;
+        break;
+    case BITNESS_32:
+        base[address + 0] = (value >> 24) & 0xff;
+        base[address + 1] = (value >> 16) & 0xff;
+        base[address + 2] = (value >> 8) & 0xff;
+        base[address + 3] = value & 0xff;
+        break;
+    }
+}
+
+static inline bool memory_write(
+        enum bitness bitness,
+        unsigned int address,
+        unsigned int value)
+{
+    if (is_in_range(address, ROM_START, ROM_SIZE)) {
+        memory_write_concrete(bitness, g_rom, address - ROM_START, value);
+        return true;
+    } else if (is_in_range(address, RAM_START, RAM_SIZE)) {
+        memory_write_concrete(bitness, g_ram, address - RAM_START, value);
+        return true;
+    } else if (is_in_range(address, IO1_START, IO1_SIZE)) {
+        memory_write_concrete(bitness, g_io1, address - IO1_START, value);
+        return true;
+    } else if (is_in_range(address, IO2_START, IO2_SIZE)) {
+        memory_write_concrete(bitness, g_io2, address - IO2_START, value);
+        return true;
+    }
+    return false;
+}
+
+#define MASK_24(X) ((X) & (0xFF << 24))
+
+unsigned int m68k_read_memory_8(unsigned int address)
+{
+    assert(MASK_24(address) == 0); // Just curious
+    const struct read_result ret = memory_read(BITNESS_8, address);
+    if (!ret.successful)
+        exit_error("Read error u8 @%08x", address);
+    return ret.result;
+}
+
+unsigned int m68k_read_memory_16(unsigned int address)
+{
+    assert(MASK_24(address) == 0); // Just curious
+    const struct read_result ret = memory_read(BITNESS_16, address);
+    if (!ret.successful)
+        exit_error("Read error u16 @%08x", address);
+    return ret.result;
+}
+
+unsigned int m68k_read_memory_32(unsigned int address)
+{
+    assert(MASK_24(address) == 0); // Just curious
+    const struct read_result ret = memory_read(BITNESS_32, address);
+    if (!ret.successful)
+        exit_error("Read error u32 @%08x", address);
+    return ret.result;
+}
+
+unsigned int m68k_read_disassembler_16(unsigned int address)
+{
+    assert(MASK_24(address) == 0); // Just curious
+    const struct read_result ret = memory_read(BITNESS_16, address);
+    if (!ret.successful)
+        exit_error("Disasm read error u16 @0x%08x", address);
+    return ret.result;
+}
+
+unsigned int m68k_read_disassembler_32(unsigned int address)
+{
+    assert(MASK_24(address) == 0); // Just curious
+    const struct read_result ret = memory_read(BITNESS_32, address);
+    if (!ret.successful)
+        exit_error("Disasm read error u32 @0x%08x", address);
+    return ret.result;
+}
+
+void m68k_write_memory_8(unsigned int address, unsigned int value)
+{
+    assert(MASK_24(address) == 0); // Just curious
+    const bool successful = memory_write(BITNESS_8, address, value);
+    if (!successful)
+        exit_error("Attempted to write %02x (u8) to address %08x", value&0xff, address);
+}
+
+void m68k_write_memory_16(unsigned int address, unsigned int value)
+{
+    assert(MASK_24(address) == 0); // Just curious
+    const bool successful = memory_write(BITNESS_16, address, value);
+    if (!successful)
+        exit_error("Attempted to write %04x (u16) to address %08x", value&0xffff, address);
+}
+
+void m68k_write_memory_32(unsigned int address, unsigned int value)
+{
+    assert(MASK_24(address) == 0); // Just curious
+    const bool successful = memory_write(BITNESS_16, address, value);
+    if (!successful)
+        exit_error("Attempted to write %08x (u32) to address %08x", value, address);
+}