Minimal sound implementation take 2

Makefile

@@ -27,6 +27,7 @@
 
 DEBUG ?= 0
 MEMSIZE ?= 128
+ENABLE_AUDIO ?= 1
 
 SOURCES = $(wildcard src/*.c)
 
@@ -54,7 +55,7 @@ endif
 # Basic support for changing screen res (with the MacPlusV3 ROM)
 DISP_WIDTH ?= 512
 DISP_HEIGHT ?= 342
-CFLAGS_CFG = -DDISP_WIDTH=$(DISP_WIDTH) -DDISP_HEIGHT=$(DISP_HEIGHT)
+CFLAGS_CFG = -DDISP_WIDTH=$(DISP_WIDTH) -DDISP_HEIGHT=$(DISP_HEIGHT) -DENABLE_AUDIO=$(ENABLE_AUDIO)
 
 all:	main
 

include/machw.h

@@ -81,6 +81,8 @@ extern int overlay;
  * But, that should never happen post-boot.
  */
 #define CLAMP_RAM_ADDR(x) ((x) >= RAM_SIZE ? (x) % RAM_SIZE : (x))
+/* Is the address (previously clamped with CLAMP_RAM_ADDR) the audio trap address? (last byte of audio data) */
+#define IS_RAM_AUDIO_TRAP(x) (x == umac_get_audio_offset() + 2 * 369)
 
 #define IS_VIA(x)       ((ADR24(x) & 0xe80000) == 0xe80000)
 #define IS_IWM(x)       ((ADR24(x) >= 0xdfe1ff) && (ADR24(x) < (0xdfe1ff + 0x2000)))

include/umac.h

@@ -53,4 +53,11 @@ static inline unsigned int      umac_get_fb_offset(void)
         return RAM_SIZE - ((DISP_WIDTH * DISP_HEIGHT / 8) + 0x380);
 }
 
+#if ENABLE_AUDIO
+#define umac_get_audio_offset() (RAM_SIZE - 768)
+
+void umac_audio_trap();
+void umac_audio_cfg(int volume, int sndres);
+#endif
+
 #endif

src/main.c

@@ -40,6 +40,7 @@
 #include <errno.h>
 #include <setjmp.h>
 
+#include "umac.h"
 #include "machw.h"
 #include "m68k.h"
 #include "via.h"
@@ -70,6 +71,9 @@ static unsigned int g_int_controller_highest_int = 0;  /* Highest pending interr
 uint8_t *_ram_base;
 uint8_t *_rom_base;
 
+#if ENABLE_AUDIO
+static int umac_volume, umac_sndres;
+#endif
 int overlay = 1;
 static uint64_t global_time_us = 0;
 static int sim_done = 0;
@@ -155,6 +159,14 @@ static void     via_ra_changed(uint8_t val)
                 update_overlay_layout();
         }
 
+#if ENABLE_AUDIO
+        uint8_t vol = val & 7;
+        if (vol != umac_volume) {
+                umac_volume = val & 7;
+                umac_audio_cfg(umac_volume, umac_sndres);
+        }
+#endif
+
         oldval = val;
 }
 
@@ -166,7 +178,15 @@ static void     via_rb_changed(uint8_t val)
         // 4 = mouse4 (in, mouse X2)
         // 3 = mouse7 (in, 0 = button pressed)
         // [2:0] = RTC controls
+#if ENABLE_AUDIO
+        uint8_t sndres = val >> 7;
+        if(sndres != umac_sndres) {
+                umac_sndres = sndres;
+                umac_audio_cfg(umac_volume, umac_sndres);
+        }
+#else
         (void)val;
+#endif
 }
 
 static uint8_t  via_ra_in(void)
@@ -437,7 +457,13 @@ unsigned int    cpu_read_long_dasm(unsigned int address)
 void    FAST_FUNC(cpu_write_byte)(unsigned int address, unsigned int value)
 {
         if (IS_RAM(address)) {
-                RAM_WR8(CLAMP_RAM_ADDR(address), value);
+                address = CLAMP_RAM_ADDR(address);
+                RAM_WR8(address, value);
+#if ENABLE_AUDIO
+                if(IS_RAM_AUDIO_TRAP(address)) {
+                        umac_audio_trap();
+                }
+#endif
                 return;
         }
 

src/rom.c

@@ -116,6 +116,9 @@ static void     rom_patch_plusv3(uint8_t *rom_base)
          * allowing the ROM checksum to fail (it returns failure, then
          * we carry on).  This avoids wild RAM addrs being accessed.
          */
+
+        /* Fix up the sound buffer as used by BootBeep */
+        ROM_WR32(0x292, RAM_SIZE - 768);
 #endif
 
 #if DISP_WIDTH != 512 || DISP_HEIGHT != 342

src/unix_main.c

@@ -27,6 +27,7 @@
  * SOFTWARE.
  */
 
+#include <assert.h>
 #include <stdio.h>
 #include <fcntl.h>
 #include <getopt.h>
@@ -35,6 +36,9 @@
 #include <sys/time.h>
 #include <string.h>
 #include <unistd.h>
+#if ENABLE_AUDIO
+#include <stdatomic.h>
+#endif
 #include "SDL.h"
 
 #include "rom.h"
@@ -78,6 +82,42 @@ static void     copy_fb(uint32_t *fb_out, uint8_t *fb_in)
         }
 }
 
+#if ENABLE_AUDIO
+// audio_callback is called from a thread, so pending_v_retrace can't be a regular variable
+atomic_int pending_v_retrace;
+static int volscale;
+uint8_t *audio_base;
+
+int16_t audio[370];
+
+void umac_audio_cfg(int umac_volume, int umac_sndres) {
+        volscale = umac_sndres ? 0 : 65536 * umac_volume / 7;
+}
+
+void umac_audio_trap() {
+        int32_t  offset = 128;
+        uint16_t *audiodata = (uint16_t*)audio_base;
+        int scale = volscale;
+        if (!scale) {
+                memset(audio, 0, sizeof(audio));
+                return;
+        }
+        int16_t *stream = audio;
+        for(int i=0; i<370; i++) {
+                int32_t a = (*audiodata++ & 0xff) - offset;
+                a = (a * scale) >> 8;
+                *stream++ = a;
+        }
+}
+
+static void audio_callback(void *userdata, Uint8 *stream_in, int len_bytes) {
+        (void) userdata;
+        assert(len_bytes == sizeof(audio));
+        atomic_store(&pending_v_retrace, 1);
+        memcpy(stream_in, audio, sizeof(audio));
+}
+#endif
+
 /**********************************************************************/
 
 /* The emulator core expects to be given ROM and RAM pointers,
@@ -232,7 +272,11 @@ int     main(int argc, char *argv[])
         SDL_Renderer *renderer;
         SDL_Texture *texture;
 
-        SDL_Init(SDL_INIT_VIDEO);
+        SDL_Init(SDL_INIT_VIDEO
+#if ENABLE_AUDIO
+                | SDL_INIT_AUDIO
+#endif
+);
         SDL_Window *window = SDL_CreateWindow("umac",
                                               SDL_WINDOWPOS_UNDEFINED,
                                               SDL_WINDOWPOS_UNDEFINED,
@@ -264,18 +308,47 @@ int     main(int argc, char *argv[])
                 return 1;
         }
 
+#if ENABLE_AUDIO
+        SDL_AudioSpec desired, obtained;
+
+        audio_base = (uint8_t*)ram_base + umac_get_audio_offset();
+
+        SDL_zero(desired);
+        desired.freq = 22256; // wat
+        desired.channels = 1;
+        desired.samples = 370;
+        desired.userdata = (uint8_t*)ram_base + umac_get_audio_offset();
+        desired.callback = audio_callback;
+        desired.format = AUDIO_S16;
+
+        SDL_AudioDeviceID audio_device = SDL_OpenAudioDevice(NULL, 0, &desired, &obtained, 0);
+        if (!audio_device) {
+                char buf[500];
+                SDL_GetErrorMsg(buf, sizeof(buf));
+                printf("SDL audio_deviceSDL_GetError() -> %s\n", buf);
+                return 1;
+        }
+#endif
+
         ////////////////////////////////////////////////////////////////////////
         // Emulator init
 
         umac_init(ram_base, rom_base, discs);
         umac_opt_disassemble(opt_disassemble);
 
+#if ENABLE_AUDIO
+        // Default state is paused, this unpauses it
+        SDL_PauseAudioDevice(audio_device, 0);
+#endif
+
         ////////////////////////////////////////////////////////////////////////
         // Main loop
 
         int done = 0;
         int mouse_button = 0;
+#if !ENABLE_AUDIO
         uint64_t last_vsync = 0;
+#endif
         uint64_t last_1hz = 0;
         do {
                 struct timeval tv_now;
@@ -321,11 +394,14 @@ int     main(int argc, char *argv[])
                 uint64_t now_usec = (tv_now.tv_sec * 1000000) + tv_now.tv_usec;
 
                 /* Passage of time: */
-                if ((now_usec - last_vsync) >= 16667) {
+#if ENABLE_AUDIO
+                int do_v_retrace = atomic_exchange(&pending_v_retrace, 0);
+#else
+                int do_v_retrace = (now_usec - last_vsync) >= 16667;
+#endif
+                if (do_v_retrace) {
                         umac_vsync_event();
-                        last_vsync = now_usec;
 
-                        /* Cheapo framerate limiting: */
                         copy_fb(framebuffer, ram_get_base() + umac_get_fb_offset());
                         SDL_UpdateTexture(texture, NULL, framebuffer,
                                           DISP_WIDTH * sizeof (Uint32));