add preliminary apu register support

1 files changed, 55 insertions, 0 deletions

diff --git a/apu.c b/apu.c
new file mode 100644
index 0000000..3c0393c
--- /dev/null
+++ b/apu.c
@@ -0,0 +1,55 @@
+#include <stdio.h>
+#include <string.h>
+
+#include "apu.h"
+
+struct apu apu = {0};
+
+void
+apu_init(void)
+{
+        memset(&apu, 0, sizeof(apu));
+}
+
+uint8_t
+apu_read(uint16_t addr)
+{
+        switch (addr) {
+        /* pulse1 */
+        case 0x4000:
+                return (apu.pulse1.duty << 6) | (apu.pulse1.envelope << 5)
+                    | (apu.pulse1.const_vol << 4) | apu.pulse1.envelope_vol;
+        case 0x4001:
+                return (apu.pulse1.sweep_enable << 7) | (apu.pulse1.sweep_period << 4)
+                    | (apu.pulse1.sweep_negative << 3) | apu.pulse1.sweep_shift_count;
+        case 0x4002:
+                return apu.pulse1.timer_low;
+        case 0x4003:
+                return (apu.pulse1.length_counter_load << 3) | apu.pulse1.timer_high;
+        /* pulse2 */
+        case 0x4004:
+                return (apu.pulse2.duty << 6) | (apu.pulse2.envelope << 5)
+                    | (apu.pulse2.const_vol << 4) | apu.pulse2.envelope_vol;
+        case 0x4005:
+                return (apu.pulse1.sweep_enable << 7) | (apu.pulse1.sweep_period << 4)
+                    | (apu.pulse1.sweep_negative << 3) | apu.pulse1.sweep_shift_count;
+        case 0x4006:
+                return apu.pulse1.timer_low;
+        case 0x4007:
+                return (apu.pulse1.length_counter_load << 3) | apu.pulse1.timer_high;
+        /* status */
+        case 0x4015:
+                return (apu.status.dmc_int << 7) | (apu.status.frame_int << 6)
+                    | (apu.status.dmc_active << 4) | (apu.status.lc_noise << 3)
+                    | (apu.status.lc_triangle << 2) | (apu.status.lc_pulse2 << 1)
+                    | apu.status.lc_pulse1;
+        default:
+                fprintf(stderr, "Invalid APU read at $%04X!\n", addr);
+                return 0;
+        };
+}
+
+void
+apu_write(uint16_t addr, uint8_t byte)
+{
+}