Kernel: First cut of a sb16 driver

Also add an AudioServer that (right now) doesn't do much.
It tries to open, parse, and play a wav file. In the future, it can do more.

My general thinking here here is that /dev/audio will be "owned" by AudioServer,
and we'll do mixing in software before passing buffers off to the kernel
to play, but we have to start somewhere.

Kernel/Devices/SB16.cpp

@@ -0,0 +1,179 @@
+#include "SB16.h"
+#include "IO.h"
+#include <Kernel/VM/MemoryManager.h>
+
+const u16 DSP_READ = 0x22A;
+const u16 DSP_WRITE = 0x22C;
+const u16 DSP_STATUS = 0x22E;
+const u16 DSP_R_ACK = 0x22F;
+
+/* Write a value to the DSP write register */
+void SB16::dsp_write(u8 value)
+{
+    while (IO::in8(DSP_WRITE) & 0x80) {
+        ;
+    }
+    IO::out8(DSP_WRITE, value);
+}
+
+/* Reads the value of the DSP read register */
+u8 SB16::dsp_read()
+{
+    while (!(IO::in8(DSP_STATUS) & 0x80)) {
+        ;
+    }
+    return IO::in8(DSP_READ);
+}
+
+/* Changes the sample rate of sound output */
+void SB16::set_sample_rate(uint16_t hz)
+{
+    dsp_write(0x41); // output
+    dsp_write((u8)(hz >> 8));
+    dsp_write((u8)hz);
+    dsp_write(0x42); // input
+    dsp_write((u8)(hz >> 8));
+    dsp_write((u8)hz);
+}
+
+static SB16* s_the;
+
+SB16::SB16()
+    : IRQHandler(5)
+    , CharacterDevice(42, 42) // ### ?
+{
+    s_the = this;
+    initialize();
+}
+
+SB16::~SB16()
+{
+}
+
+SB16& SB16::the()
+{
+    return *s_the;
+}
+
+void SB16::handle_irq()
+{
+    m_interrupted = true;
+
+    // Stop sound output ready for the next block.
+    dsp_write(0xd0);
+
+    IO::in8(DSP_STATUS); // 8 bit interrupt
+    if (m_major_version >= 4)
+        IO::in8(DSP_R_ACK); // 16 bit interrupt
+}
+
+void SB16::initialize()
+{
+    IO::out8(0x226, 1);
+    IO::delay();
+    IO::out8(0x226, 0);
+
+    auto data = dsp_read();
+    if (data != 0xaa) {
+        kprintf("SB16: sb not ready");
+        return;
+    }
+
+    // Get the version info
+    dsp_write(0xe1);
+    m_major_version = dsp_read();
+    auto vmin = dsp_read();
+
+    kprintf("SB16: found version %d.%d\n", m_major_version, vmin);
+    enable_irq();
+}
+
+bool SB16::can_read(FileDescription&) const
+{
+    return false;
+}
+
+ssize_t SB16::read(FileDescription&, u8*, ssize_t)
+{
+    return 0;
+}
+
+void SB16::dma_start(uint32_t length)
+{
+    const auto addr = m_dma_buffer_page->paddr().get();
+    const u8 channel = 1;
+    const u8 mode = 0;
+
+    // Disable the DMA channel
+    IO::out8(0x0a, 4 + (channel % 4));
+
+    // Clear the byte pointer flip-flop
+    IO::out8(0x0c, 0);
+
+    // Write the DMA mode for the transfer
+    IO::out8(0x0b, channel | mode);
+
+    // Write the offset of the buffer
+    IO::out8(0x02, (u8)addr);
+    IO::out8(0x02, (u8)(addr >> 8));
+
+    // Write the transfer length
+    IO::out8(0x03, (u8)(length - 1));
+    IO::out8(0x03, (u8)((length - 1) >> 8));
+
+    // Write the buffer
+    IO::out8(0x83, addr >> 16);
+
+    // Enable the DMA channel
+    IO::out8(0x0a, channel);
+}
+
+void SB16::wait_for_irq()
+{
+    m_interrupted = false;
+#ifdef SB16_DEBUG
+    kprintf("SB16: waiting for interrupt...\n");
+#endif
+    // FIXME: Add timeout.
+    while (!m_interrupted) {
+        // FIXME: Put this process into a Blocked state instead, it's stupid to wake up just to check a flag.
+        Scheduler::yield();
+    }
+#ifdef SB16_DEBUG
+    kprintf("SB16: got interrupt!\n");
+#endif
+    memory_barrier();
+}
+
+ssize_t SB16::write(FileDescription&, const u8* data, ssize_t length)
+{
+    if (!m_dma_buffer_page) {
+        kprintf("SB16: Allocating page\n");
+        m_dma_buffer_page = MM.allocate_supervisor_physical_page();
+    }
+
+    kprintf("SB16: Writing buffer of %d bytes\n", length);
+    const int BLOCK_SIZE = 32 * 1024;
+    if (length > BLOCK_SIZE) {
+        return -ENOSPC;
+    }
+    const u8 mode = 0;
+
+    disable_irq();
+    const int sample_rate = 44100;
+    set_sample_rate(sample_rate);
+    dma_start(length);
+    memcpy(m_dma_buffer_page->paddr().as_ptr(), data, length);
+
+    u8 command = 0x06;
+    command |= 0xc0;
+
+    dsp_write(command);
+    dsp_write(mode);
+    dsp_write((u8)length);
+    dsp_write((u8)(length >> 8));
+
+    enable_irq();
+    wait_for_irq();
+    return length;
+}