WIP

Enable ALSA driver and System V IPC in Linux Kernel.

Implement VIRTIO_SND_R_PCM_* actions.

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.

Freeze at pcm_stop as the device does not receive any data
for playing sound.

Author: Cuda-Chen

.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 :=
+
 # virtio-blk
 ENABLE_VIRTIOBLK ?= 1
 $(call set-feature, VIRTIOBLK)
@@ -41,6 +44,36 @@ ifeq ($(call has, VIRTIONET), 1)
     OBJS_EXTRA += virtio-net.o
 endif
 
+# virtio-snd
+ENABLE_VIRTIOSND ?= 1
+ifneq ($(UNAME_S),Linux)
+    ENABLE_VIRTIOSND := 0
+endif
+
+ifeq (0, $(call check-alsa))
+$(warning No libasound installed. Check libasound in advance.)
+    ENABLE_VIRTIOSND := 0
+endif
+$(call set-feature, VIRTIOSND)
+ifeq ($(call has, VIRTIOSND), 1)
+    OBJS_EXTRA += virtio-snd.o
+    LDFLAGS += -lasound -lpthread
+    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
 

cnfa

@@ -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/buildroot.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 +937,9 @@ 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
 
 #
 # HID support

configs/linux.config

@@ -190,6 +190,53 @@ 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 {
@@ -205,4 +252,8 @@ 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;

device.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

feature.h

@@ -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);
@@ -581,6 +606,11 @@ 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;
@@ -603,6 +633,11 @@ 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]);