starting on lcd

cli/compile.sh

@@ -1,6 +1,6 @@
 #!/bin/sh
 mkdir -p build
 cd build
-cmake ..
+cmake -DCMAKE_BUILD_TYPE=Debug ..
 make
 cd ..

cli/emulator.c

@@ -3,13 +3,16 @@
 #include "dmg.h"
 #include "cpu.h"
 #include "rom.h"
+#include "lcd.h"
 
 int main(int argc, char *argv[])
 {
     struct cpu cpu;
     struct rom rom;
     struct dmg dmg;
-    int executed = 0;
+    struct lcd lcd;
+
+    int executed;
 
     if (argc < 2) {
         printf("no rom specified\n");
@@ -24,12 +27,12 @@ int main(int argc, char *argv[])
     // this might be too much abstraction but it'll let me
     // test the cpu, rom, and dmg independently and use the cpu
     // for other non-GB stuff
-    dmg_new(&dmg, &cpu, &rom);
+    dmg_new(&dmg, &cpu, &rom, &lcd);
     cpu_bind_mem_model(&cpu, &dmg, dmg_read, dmg_write);
 
     cpu.pc = 0;
 
-    for (; executed < 100000; executed++) {
+    for (executed = 0; executed < 100000; executed++) {
         cpu_step(&cpu);
     }
 

src/dmg.c

@@ -2,14 +2,16 @@
 
 #include "cpu.h"
 #include "rom.h"
+#include "lcd.h"
 #include "dmg.h"
 #include "types.h"
 #include "bootstrap.h"
 
-void dmg_new(struct dmg *dmg, struct cpu *cpu, struct rom *rom)
+void dmg_new(struct dmg *dmg, struct cpu *cpu, struct rom *rom, struct lcd *lcd)
 {
     dmg->cpu = cpu;
     dmg->rom = rom;
+    dmg->lcd = lcd;
 }
 
 u8 dmg_read(void *_dmg, u16 address)
@@ -30,10 +32,13 @@ u8 dmg_read(void *_dmg, u16 address)
         return 0;
     } else if (address < 0xe000) {
         return dmg->main_ram[address - 0xc000];
+    } else if (lcd_is_valid_addr(address)) {
+        return lcd_read(dmg->lcd, address);
     } else if (address >= 0xff80 && address <= 0xfffe) {
         return dmg->zero_page[address - 0xff80];
     } else {
         // not sure about any of this yet
+        fprintf(stderr, "don't know how to read 0x%04x\n", address);
         return 0;
     }
 }
@@ -54,9 +59,22 @@ void dmg_write(void *_dmg, u16 address, u8 data)
         // TODO switchable ram bank
     } else if (address < 0xe000) {
         dmg->main_ram[address - 0xc000] = data;
+    } else if (lcd_is_valid_addr(address)) {
+        lcd_write(dmg->lcd, address, data);
     } else if (address >= 0xff80 && address <= 0xfffe) {
         dmg->zero_page[address - 0xff80] = data;
     } else {
         // not sure about any of this yet
     }
 }
+
+void dmg_step(void *_dmg)
+{
+    struct dmg *dmg = (struct dmg *) _dmg;
+
+    // order of dependencies? i think cpu needs to step first then update
+    // all other hw
+    cpu_step(dmg->cpu);
+
+    lcd_step(dmg->lcd);
+}

src/dmg.h

@@ -13,9 +13,12 @@ struct dmg {
     u8 zero_page[0x80];
 };
 
-void dmg_new(struct dmg *dmg, struct cpu *cpu, struct rom *rom);
+void dmg_new(struct dmg *dmg, struct cpu *cpu, struct rom *rom, struct lcd *lcd);
 
+// why did i make these void *
 u8 dmg_read(void *dmg, u16 address);
 void dmg_write(void *dmg, u16 address, u8 data);
 
+void dmg_step(void *dmg);
+
 #endif

src/lcd.c

@@ -3,6 +3,35 @@
 #include "types.h"
 #include "lcd.h"
 
+static void set_bit(struct lcd *lcd, u16 addr, u8 bit)
+{
+    lcd_write(lcd, addr, lcd_read(lcd, addr) | (1 << bit));
+}
+
+static void clear_bit(struct lcd *lcd, u16 addr, u8 bit)
+{
+    lcd_write(lcd, addr, lcd_read(lcd, addr) & ~(1 << bit));
+}
+
+u8 lcd_is_valid_addr(u16 addr)
+{
+    return addr >= REG_LCD_BASE && addr <= REG_LCD_LAST;
+}
+
+u8 lcd_read(struct lcd *lcd, u16 addr)
+{
+    return lcd->regs[addr - REG_LCD_BASE];
+}
+
+void lcd_write(struct lcd *lcd, u16 addr, u8 value)
+{
+    if (addr == REG_LY) {
+        // writing to this register always resets it
+        value = 0;
+    }
+    lcd->regs[addr - REG_LCD_BASE] = value;
+}
+
 void lcd_put_pixel(struct lcd *lcd, u8 x, u8 y, u8 value)
 {
     if (x >= LCD_WIDTH || y >= LCD_HEIGHT) {
@@ -10,4 +39,18 @@ void lcd_put_pixel(struct lcd *lcd, u8 x, u8 y, u8 value)
         return;
     }
     lcd->pixels[y * LCD_WIDTH + x] = value;
+}
+
+void lcd_step(struct lcd *lcd)
+{
+    // update LYC
+    if (lcd_read(lcd, REG_LY) == lcd_read(lcd, REG_LYC)) {
+        set_bit(lcd, REG_STAT, STAT_FLAG_MATCH);
+    } else {
+        clear_bit(lcd, REG_STAT, STAT_FLAG_MATCH);
+    }
+
+    // step to next scanline 0-153
+    u8 next_scanline = (lcd_read(lcd, REG_LY) + 1) % 154;
+    lcd_write(lcd, REG_LY, next_scanline);
 }

src/lcd.h

@@ -6,10 +6,37 @@
 #define LCD_WIDTH 160
 #define LCD_HEIGHT 144
 
+#define REG_LCD_BASE 0xff40
+
+#define REG_LCDC 0xff40
+#define REG_STAT 0xff41
+#define REG_SCY  0xff42
+#define REG_SCX  0xff43
+#define REG_LY   0xff44
+#define REG_LYC  0xff45
+#define REG_DMA  0xff46
+#define REG_BGP  0xff47
+#define REG_OBP0 0xff48
+#define REG_OBP1 0xff49
+#define REG_WY   0xff4a
+#define REG_WX   0xff4b
+
+#define REG_LCD_LAST REG_WX
+
+#define STAT_FLAG_MATCH 2
+
 struct lcd {
+    u8 regs[0x0c];
     u8 *pixels;
 };
 
+u8 lcd_is_valid_addr(u16 addr);
+u8 lcd_read(struct lcd *lcd, u16 addr);
+void lcd_write(struct lcd *lcd, u16 addr, u8 value);
+
 void lcd_put_pixel(struct lcd *lcd, u8 x, u8 y, u8 value);
 
+// i feel like i'm going to need to call this every cycle and update regs
+void lcd_step(struct lcd *lcd);
+
 #endif