WIP

Enable ALSA driver and System V IPC in Linux Kernel. For
ALSA, the debug is enabled and will be removed once
this commit is ready.

Add description of descriptor chaining, yet need refactoring
the description as well as code (exists uncertainty of
the query struct).

Succeed to initialize virtio-snd.

Handle requests in control and TX queue, and print the address and length
of each virtq element to check the validness of self-implement
queue.

For macOS, an experimental core audio library check is implemented.

As the driver sends the PCM frames asynchronously, use a dedicated
thread for receiving frames from driver.

The reason that pcm_release state hangs is because of PulseAudio,
need to address this later.

Add ring buffer struct so that we don't need to allocate
space frequently.
However, the white noise produced by speaker-test does
not come out.

.github/workflows/main.yml

@@ -10,6 +10,7 @@ jobs:
     - name: install-dependencies
       run: |
             sudo apt-get install build-essential device-tree-compiler expect
+            sudo apt-get install libasound2-dev libudev-dev
     - name: default build
       run: make
       shell: bash

.gitmodules

@@ -0,0 +1,4 @@
+[submodule "cnfa"]
+    path = cnfa
+    url = https://github.com/cntools/cnfa
+    shallow = true

Makefile

@@ -1,4 +1,5 @@
 include mk/common.mk
+include mk/check-libs.mk
 
 CC ?= gcc
 CFLAGS := -O2 -g -Wall -Wextra
@@ -13,6 +14,8 @@ OBJS_EXTRA :=
 # command line option
 OPTS :=
 
+LDFLAGS := -lm
+
 # virtio-blk
 ENABLE_VIRTIOBLK ?= 1
 $(call set-feature, VIRTIOBLK)
@@ -43,6 +46,51 @@ ifeq ($(call has, VIRTIONET), 1)
     OBJS_EXTRA += netdev.o
 endif
 
+# virtio-snd
+ENABLE_VIRTIOSND ?= 1
+ifneq ($(UNAME_S),$(filter $(UNAME_S),Linux Darwin))
+    ENABLE_VIRTIOSND := 0
+endif
+
+# Check ALSA installation
+ifeq ($(UNAME_S),Linux)
+    ifeq (0, $(call check-alsa))
+        $(warning No libasound installed. Check libasound in advance.)
+        ENABLE_VIRTIOSND := 0
+    endif
+endif
+# Check core audio installation
+ifeq ($(UNAME_S),Darwin)
+    ifeq (0, $(call check-coreaudio))
+        $(warning No CoreAudio framework installed.)
+        ENABLE_VIRTIOSND := 0
+    endif
+endif
+$(call set-feature, VIRTIOSND)
+ifeq ($(call has, VIRTIOSND), 1)
+    OBJS_EXTRA += virtio-snd.o
+
+    ifeq ($(UNAME_S),Linux)
+        LDFLAGS += -lasound -lpthread
+    else ifeq ($(UNAME_S),Darwin)
+        LDFLAGS += -framework AudioToolbox -lpthread
+    endif
+    CFLAGS += -Icnfa
+
+cnfa/Makefile:
+	git submodule update --init cnfa
+cnfa/os_generic: cnfa/Makefile
+	$(MAKE) -C $(dir $<) os_generic.h
+CNFA_LIB := cnfa/CNFA_sf.h
+$(CNFA_LIB): cnfa/Makefile cnfa/os_generic
+	$(MAKE) -C $(dir $<) CNFA_sf.h
+main.o: $(CNFA_LIB)
+endif
+
+# .DEFAULT_GOAL should be set to all since the very first target is not all
+# after git submodule.
+.DEFAULT_GOAL := all
+
 BIN = semu
 all: $(BIN) minimal.dtb
 

README.md

@@ -9,7 +9,10 @@ A minimalist RISC-V system emulator capable of running Linux the kernel and corr
 - UART: 8250/16550
 - PLIC (platform-level interrupt controller): 32 interrupts, no priority
 - Standard SBI, with the timer extension
-- VirtIO: virtio-blk acquires disk image from the host, and virtio-net is mapped as TAP interface
+- Three types of I/O support using VirtIO standard:
+    - virtio-blk acquires disk image from the host.
+    - virtio-net is mapped as TAP interface.
+    - virtio-snd uses ALSA for sound operation.
 
 ## Prerequisites
 

configs/buildroot.config

@@ -36,6 +36,9 @@ BR2_RELRO_NONE=y
 # BR2_RELRO_PARTIAL is not set
 # BR2_RELRO_FULL is not set
 BR2_FORTIFY_SOURCE_1=y
+BR2_PACKAGE_ALSA_UTILS=y
+BR2_PACKAGE_ALSA_UTILS_APLAY=y
+BR2_PACKAGE_ALSA_UTILS_SPEAKER_TEST=y
 # BR2_PACKAGE_URANDOM_SCRIPTS is not set
 BR2_TARGET_ROOTFS_CPIO=y
 BR2_TARGET_ROOTFS_CPIO_FULL=y

configs/linux.config

@@ -30,7 +30,8 @@ CONFIG_LOCALVERSION_AUTO=y
 CONFIG_BUILD_SALT=""
 CONFIG_DEFAULT_INIT=""
 CONFIG_DEFAULT_HOSTNAME="(none)"
-# CONFIG_SYSVIPC is not set
+CONFIG_SYSVIPC=y
+CONFIG_SYSVIPC_SYSCTL=y
 # CONFIG_POSIX_MQUEUE is not set
 # CONFIG_WATCH_QUEUE is not set
 # CONFIG_CROSS_MEMORY_ATTACH is not set
@@ -936,7 +937,12 @@ CONFIG_DUMMY_CONSOLE_ROWS=25
 # end of Console display driver support
 # end of Graphics support
 
-# CONFIG_SOUND is not set
+CONFIG_SOUND=y
+CONFIG_SND=y
+CONFIG_SND_VIRTIO=y
+CONFIG_SND_VERBOSE_PRINTK=y
+CONFIG_SND_DEBUG=y
+CONFIG_SND_DEBUG_VERBOSE=y
 
 #
 # HID support

device.h

@@ -191,6 +191,53 @@ void clint_write(hart_t *vm,
                  uint8_t width,
                  uint32_t value);
 
+/* VirtIO-Sound */
+
+#if SEMU_HAS(VIRTIOSND)
+#define IRQ_VSND 4
+#define IRQ_VSND_BIT (1 << IRQ_VSND)
+
+typedef struct {
+    uint32_t QueueNum;
+    uint32_t QueueDesc;
+    uint32_t QueueAvail;
+    uint32_t QueueUsed;
+    uint16_t last_avail;
+    bool ready;
+} virtio_snd_queue_t;
+
+typedef struct {
+    /* feature negotiation */
+    uint32_t DeviceFeaturesSel;
+    uint32_t DriverFeatures;
+    uint32_t DriverFeaturesSel;
+    /* queue config */
+    uint32_t QueueSel;
+    virtio_snd_queue_t queues[4];
+    /* status */
+    uint32_t Status;
+    uint32_t InterruptStatus;
+    /* supplied by environment */
+    uint32_t *ram;
+    /* implementation-specific */
+    void *priv;
+} virtio_snd_state_t;
+
+void virtio_snd_read(hart_t *core,
+                     virtio_snd_state_t *vsnd,
+                     uint32_t addr,
+                     uint8_t width,
+                     uint32_t *value);
+
+void virtio_snd_write(hart_t *core,
+                      virtio_snd_state_t *vsnd,
+                      uint32_t addr,
+                      uint8_t width,
+                      uint32_t value);
+
+bool virtio_snd_init(virtio_snd_state_t *vsnd);
+#endif /* SEMU_HAS(VIRTIOSND) */
+
 /* memory mapping */
 
 typedef struct {
@@ -206,4 +253,8 @@ typedef struct {
     virtio_blk_state_t vblk;
 #endif
     clint_state_t clint;
+#if SEMU_HAS(VIRTIOSND)
+    virtio_snd_state_t vsnd;
+#endif
+    uint64_t timer;
 } emu_state_t;

feature.h

@@ -12,5 +12,10 @@
 #define SEMU_FEATURE_VIRTIONET 1
 #endif
 
+/* virtio-snd */
+#ifndef SEMU_FEATURE_VIRTIOSND
+#define SEMU_FEATURE_VIRTIOSND 1
+#endif
+
 /* Feature test macro */
 #define SEMU_HAS(x) SEMU_FEATURE_##x

main.c

@@ -81,6 +81,18 @@ static void emu_update_timer_interrupt(hart_t *hart)
     clint_update_interrupts(hart, &data->clint);
 }
 
+#if SEMU_HAS(VIRTIOSND)
+static void emu_update_vsnd_interrupts(vm_t *vm)
+{
+    emu_state_t *data = PRIV(vm->hart[0]);
+    if (data->vsnd.InterruptStatus)
+        data->plic.active |= IRQ_VSND_BIT;
+    else
+        data->plic.active &= ~IRQ_VSND_BIT;
+    plic_update_interrupts(vm, &data->plic);
+}
+#endif
+
 static void mem_load(hart_t *hart,
                      uint32_t addr,
                      uint8_t width,
@@ -121,6 +133,13 @@ static void mem_load(hart_t *hart,
             clint_read(hart, &data->clint, addr & 0xFFFFF, width, value);
             clint_update_interrupts(hart, &data->clint);
             return;
+
+#if SEMU_HAS(VIRTIOSND)
+        case 0x44: /* virtio-snd */
+            virtio_snd_read(hart, &data->vsnd, addr & 0xFFFFF, width, value);
+            emu_update_vsnd_interrupts(hart->vm);
+            return;
+#endif
         }
     }
     vm_set_exception(hart, RV_EXC_LOAD_FAULT, hart->exc_val);
@@ -166,6 +185,12 @@ static void mem_store(hart_t *hart,
             clint_write(hart, &data->clint, addr & 0xFFFFF, width, value);
             clint_update_interrupts(hart, &data->clint);
             return;
+#if SEMU_HAS(VIRTIOSND)
+        case 0x44: /* virtio-snd */
+            virtio_snd_write(hart, &data->vsnd, addr & 0xFFFFF, width, value);
+            emu_update_vsnd_interrupts(hart->vm);
+            return;
+#endif
         }
     }
     vm_set_exception(hart, RV_EXC_STORE_FAULT, hart->exc_val);
@@ -591,6 +616,11 @@ static int semu_start(int argc, char **argv)
     emu.vblk.ram = emu.ram;
     emu.disk = virtio_blk_init(&(emu.vblk), disk_file);
 #endif
+#if SEMU_HAS(VIRTIOSND)
+    if (!virtio_snd_init(&(emu.vsnd)))
+        fprintf(stderr, "No virtio-snd functioned\n");
+    emu.vsnd.ram = emu.ram;
+#endif
 
     /* Emulate */
     uint32_t peripheral_update_ctr = 0;
@@ -613,6 +643,11 @@ static int semu_start(int argc, char **argv)
                 if (emu.vblk.InterruptStatus)
                     emu_update_vblk_interrupts(&vm);
 #endif
+
+#if SEMU_HAS(VIRTIOSND)
+                if (emu.vsnd.InterruptStatus)
+                    emu_update_vsnd_interrupts(&vm);
+#endif
             }
 
             emu_update_timer_interrupt(vm.hart[i]);

minimal.dts

@@ -63,5 +63,13 @@
             interrupts = <3>;
         };
 #endif
+
+#if SEMU_FEATURE_VIRTIOSND
+        snd0: virtio@4400000 {
+            compatible = "virtio,mmio";
+            reg = <0x4400000 0x200>;
+            interrupts = <4>;
+        };
+#endif
     };
 };

mk/check-libs.mk

@@ -0,0 +1,35 @@
+# Create a mininal ALSA program
+define create-alsa-prog
+echo '\
+#include <alsa/asoundlib.h>\n\
+int main(){\n\
+    snd_pcm_t *pcm;\n\
+    snd_pcm_open(&pcm, "default", SND_PCM_STREAM_PLAYBACK, 0);\n\
+    snd_pcm_close(pcm);\n\
+    return 0;\n\
+}\n'
+endef
+
+# Create a mininal Core Audio program
+define create-coreaudio-prog
+echo '\
+#include <CoreAudio/CoreAudio.h>\n\
+int main(){\n\
+    AudioComponent comp;\n\
+    comp = AudioComponentFindNext(NULL, &desc);\n\
+    if (comp == NULL) exit (-1);\n\
+    return 0;\n\
+}\n'
+endef
+
+# Check ALSA installation
+define check-alsa
+$(shell $(call create-alsa-prog) | $(CC) -x c -lasound -o /dev/null > /dev/null 2> /dev/null - 
+	&& echo $$?)
+endef
+
+# Check Core Audio installation
+define check-coreaudio
+$(shell $(call create-coreaudio-prog) | $(CC) -x c -framework CoreAudio -o /dev/null > /dev/null 2> /dev/null - 
+	&& echo $$?) 
+endef