Implement NES controller input polling

src/controller.c

@@ -0,0 +1,75 @@
+#include "./controller.h"
+
+void create_controller(controller_t *controller) {
+    controller->joy[0] = 0;
+    controller->joy[1] = 0;
+
+    controller->shift[0] = 0;
+    controller->shift[1] = 0;
+
+    controller->strobe = false;
+}
+
+void destroy_controller(controller_t *controller) {}
+
+void write_strobe_controller(controller_t *controller, unsigned char value) {
+    controller->strobe = value & 1;
+    if (controller->strobe) {
+        controller->shift[0] = controller->joy[0];
+        controller->shift[1] = controller->joy[1];
+    }
+}
+
+unsigned char read_joy1_controller(controller_t *controller) {
+    unsigned char result = controller->shift[0] & 1;
+    controller->shift[0] >>= 1;
+    controller->shift[0] |= 0x80;
+    return result;
+}
+
+unsigned char read_joy2_controller(controller_t *controller) {
+    unsigned char result = controller->shift[1] & 1;
+    controller->shift[1] >>= 1;
+    controller->shift[1] |= 0x80;
+    return result;
+}
+
+void set_joy1_controller(controller_t *controller,
+                         bool a,
+                         bool b,
+                         bool select,
+                         bool start,
+                         bool up,
+                         bool down,
+                         bool left,
+                         bool right) {
+    controller->joy[0] = 0;
+    controller->joy[0] |= a;
+    controller->joy[0] |= b << 1;
+    controller->joy[0] |= select << 2;
+    controller->joy[0] |= start << 3;
+    controller->joy[0] |= up << 4;
+    controller->joy[0] |= down << 5;
+    controller->joy[0] |= left << 6;
+    controller->joy[0] |= right << 7;
+}
+
+void set_joy2_controller(controller_t *controller,
+                         bool a,
+                         bool b,
+                         bool select,
+                         bool start,
+                         bool up,
+                         bool down,
+                         bool left,
+                         bool right) {
+    controller->joy[0] = 0;
+    controller->joy[1] |= a;
+    controller->joy[1] |= b << 1;
+    controller->joy[1] |= select << 2;
+    controller->joy[1] |= start << 3;
+    controller->joy[1] |= up << 4;
+    controller->joy[1] |= down << 5;
+    controller->joy[1] |= left << 6;
+    controller->joy[1] |= right << 7;
+}

src/controller.h

@@ -0,0 +1,114 @@
+#ifndef CONTROLLER_H
+#define CONTROLLER_H
+
+#include <stdbool.h>
+
+/**
+ * @brief NES input controller state.
+ *
+ */
+typedef struct {
+    /**
+     * @brief Button states of the controllers.
+     *
+     */
+    unsigned char joy[2];
+
+    /**
+     * @brief Shift registers for each controller.
+     *
+     */
+    unsigned char shift[2];
+
+    /**
+     * @brief Flag that determines if the controller input should be polled.
+     *
+     */
+    bool strobe;
+} controller_t;
+
+/**
+ * @brief Create a controller object.
+ *
+ * @param controller
+ */
+void create_controller(controller_t *controller);
+
+/**
+ * @brief Destroy a controller object.
+ *
+ * @param controller
+ */
+void destroy_controller(controller_t *controller);
+
+/**
+ * @brief Write to $4016.
+ *
+ * @param controller
+ * @param strobe
+ */
+void write_strobe_controller(controller_t *controller, unsigned char value);
+
+/**
+ * @brief Read the button states of the first controller.
+ *
+ * @param controller
+ * @return unsigned char
+ */
+unsigned char read_joy1_controller(controller_t *controller);
+
+/**
+ * @brief Read the button states of the second controller.
+ *
+ * @param controller
+ * @return unsigned char
+ */
+unsigned char read_joy2_controller(controller_t *controller);
+
+/**
+ * @brief Set the button states of the first controller.
+ *
+ * @param controller
+ * @param a
+ * @param b
+ * @param select
+ * @param start
+ * @param up
+ * @param down
+ * @param left
+ * @param right
+ */
+void set_joy1_controller(controller_t *controller,
+                         bool a,
+                         bool b,
+                         bool select,
+                         bool start,
+                         bool up,
+                         bool down,
+                         bool left,
+                         bool right);
+
+/**
+ * @brief Set the button states of the second controller.
+ *
+ * @param controller
+ * @param a
+ * @param b
+ * @param select
+ * @param start
+ * @param up
+ * @param down
+ * @param left
+ * @param right
+ */
+void set_joy2_controller(controller_t *controller,
+                         bool a,
+                         bool b,
+                         bool select,
+                         bool start,
+                         bool up,
+                         bool down,
+                         bool left,
+                         bool right);
+
+#endif

src/cpu_bus.c

@@ -4,11 +4,13 @@ void create_cpu_bus(cpu_bus_t *bus,
                     rom_t *rom,
                     mapper_t *mapper,
                     apu_t *apu,
-                    ppu_t *ppu) {
+                    ppu_t *ppu,
+                    controller_t *controller) {
     bus->rom = rom;
     bus->mapper = mapper;
     bus->apu = apu;
     bus->ppu = ppu;
+    bus->controller = controller;
     memset(bus->memory, 0, CPU_RAM_SIZE);
 }
 
@@ -56,6 +58,10 @@ unsigned char read_cpu_bus(cpu_bus_t *bus, address_t address) {
         case PPU_REG_OAMADDR:
         case PPU_REG_OAMDMA:
             return bus->ppu->io_databus;
+        case CTRL_REG_STROBE:
+            return read_joy1_controller(bus->controller);
+        case APU_REG_FRAME_COUNTER:
+            return read_joy2_controller(bus->controller);
         // TODO: Handle APU, controller input registers
         default:
             return bus->memory[address];
@@ -95,7 +101,10 @@ void write_cpu_bus(cpu_bus_t *bus, address_t address, unsigned char value) {
         case PPU_REG_STATUS:
             bus->ppu->io_databus = value;
             break;
-        // TODO: Handle APU, controller input registers
+        case CTRL_REG_STROBE:
+            write_strobe_controller(bus->controller, value);
+            break;
+        // TODO: Handle APU registers
         default:
             bus->memory[address] = value;
             break;

src/cpu_bus.h

@@ -2,6 +2,7 @@
 #define CPU_BUS_H
 
 #include "./apu.h"
+#include "./controller.h"
 #include "./mapper.h"
 #include "./ppu.h"
 #include "./rom.h"
@@ -57,6 +58,9 @@
 #define PPU_REG_DATA    0x2007
 #define PPU_REG_OAMDMA  0x4014
 
+// Memory mapped controller registers
+#define CTRL_REG_STROBE 0x4016
+
 /**
  * @brief Bus for memory accessing and communication between the CPU and its
  * peripherals.
@@ -98,6 +102,12 @@ typedef struct {
      *
      */
     ppu_t *ppu;
+
+    /**
+     * @brief Pointer to the input controller.
+     *
+     */
+    controller_t *controller;
 } cpu_bus_t;
 
 /**
@@ -108,12 +118,14 @@ typedef struct {
  * @param mapper
  * @param apu
  * @param ppu
+ * @param controller
  */
 void create_cpu_bus(cpu_bus_t *bus,
                     rom_t *rom,
                     mapper_t *mapper,
                     apu_t *apu,
-                    ppu_t *ppu);
+                    ppu_t *ppu,
+                    controller_t *controller);
 
 /**
  * @brief Mirror an address according to the CPU memory map.

src/emulator.c

@@ -6,11 +6,13 @@ void create_emulator(emulator_t *emu, const char *rom_path) {
     create_cpu(&emu->cpu, &emu->cpu_bus, &emu->interrupt);
     create_apu(&emu->apu, &emu->interrupt);
     create_ppu(&emu->ppu, &emu->ppu_bus, &emu->interrupt);
+    create_controller(&emu->controller);
     create_cpu_bus(&emu->cpu_bus,
                    &emu->rom,
                    &emu->mapper,
                    &emu->apu,
-                   &emu->ppu);
+                   &emu->ppu,
+                   &emu->controller);
     create_ppu_bus(&emu->ppu_bus, &emu->rom, &emu->mapper);
     reset_interrupt(&emu->interrupt);
 
@@ -28,6 +30,7 @@ void destroy_emulator(emulator_t *emu) {
     destroy_cpu(&emu->cpu);
     destroy_apu(&emu->apu);
     destroy_ppu(&emu->ppu);
+    destroy_controller(&emu->controller);
     destroy_mapper(&emu->mapper);
     unload_rom(&emu->rom);
 }

src/emulator.h

@@ -2,6 +2,7 @@
 #define EMULATOR_H
 
 #include "./apu.h"
+#include "./controller.h"
 #include "./cpu.h"
 #include "./cpu_bus.h"
 #include "./mapper.h"
@@ -45,6 +46,12 @@ typedef struct {
      */
     ppu_t ppu;
 
+    /**
+     * @brief Input controller.
+     *
+     */
+    controller_t controller;
+
     /**
      * @brief CPU bus.
      *

src/nes.c

@@ -51,14 +51,25 @@ int main(int argc, char **argv) {
             }
         }
 
-        // Handle input
+        // Handle debug input
         if (is_keydown_input(&io.input, SDLK_o)) {
             set_debug_io(&io, true);
         }
         if (is_keydown_input(&io.input, SDLK_p)) {
             set_debug_io(&io, false);
         }
 
+        // Handle controller 1 input
+        set_joy1_controller(&emu.controller,
+                            is_keydown_input(&io.input, SDLK_z),
+                            is_keydown_input(&io.input, SDLK_x),
+                            is_keydown_input(&io.input, SDLK_a),
+                            is_keydown_input(&io.input, SDLK_s),
+                            is_keydown_input(&io.input, SDLK_UP),
+                            is_keydown_input(&io.input, SDLK_DOWN),
+                            is_keydown_input(&io.input, SDLK_LEFT),
+                            is_keydown_input(&io.input, SDLK_RIGHT));
+
         // Refresh IO
         bool io_state = refresh_io(&io, &emu);
         if (!emu_state || !io_state) {