Adding skeleton that at least compiles for audio4.c

CMakeLists.txt

@@ -144,6 +144,10 @@ else()
     option(NEW_DYNAREC "Use the PCem v15 (\"new\") dynamic recompiler" OFF)
 endif()
 
+if((CMAKE_SYSTEM_NAME STREQUAL "NetBSD") OR (CMAKE_SYSTEM_NAME STREQUAL "OpenBSD"))
+    set(AUDIO4 ON)
+endif()
+
 if(WIN32)
     set(QT ON)
     option(CPPTHREADS "C++11 threads" OFF)

src/sound/CMakeLists.txt

@@ -53,7 +53,10 @@ add_library(snd OBJECT
     snd_opl_esfm.c
 )
 
-if(OPENAL)
+# TODO: Should platform-specific audio driver be here?
+if(AUDIO4)
+    target_sources(snd PRIVATE audio4.c)
+elseif(OPENAL)
     if(VCPKG_TOOLCHAIN)
         find_package(OpenAL CONFIG REQUIRED)
     elseif(MINGW)

src/sound/audio4.c

@@ -0,0 +1,51 @@
+/*
+ * 86Box     A hypervisor and IBM PC system emulator that specializes in
+ *           running old operating systems and software designed for IBM
+ *           PC systems and compatibles from 1981 through fairly recent
+ *           system designs based on the PCI bus.
+ *
+ *           This file is part of the 86Box distribution.
+ *
+ *           Interface to audio(4).
+ *
+ *
+ *
+ * Authors:  Nishi
+ *
+ *           Copyright 2025 Nishi.
+ */
+#include <stdint.h>
+
+#include <86box/sound.h>
+
+#define FREQ   SOUND_FREQ
+#define BUFLEN SOUNDBUFLEN
+
+static int midi_freq = 44100;
+static int midi_buf_size = 4410;
+
+void closeal(void){
+}
+
+void inital(void){
+}
+
+void givealbuffer(const void *buf){
+}
+
+void givealbuffer_music(const void *buf){
+}
+
+void givealbuffer_wt(const void *buf){
+}
+
+void givealbuffer_cd(const void *buf){
+}
+
+void givealbuffer_midi(const void *buf, const uint32_t size){
+}
+	
+void al_set_midi(const int freq, const int buf_size){
+    midi_freq     = freq;
+    midi_buf_size = buf_size;
+}