Sound Blaster 16
The Sound Blaster series is a family of sound cards made by Creative. For many years they were the standard audio cards on IBM PC's.
Introduction
The Sound Blaster 16 is the successor to the Sound Blaster Pro audio card found in many older computers. It was first brought out in 1992. The main improvement over the Pro is its 16-bit digital audio sampling (hence the name). Most SB16 cards are PCI compatible, as Creative made this improvement shortly after releasing the card, upgrading from ISA.
Digital Signal Processor
The DSP built into the Sound Blaster 16 supports playing and recording audio in 8-bit and 16-bit PCM encoded samples, along with playing several other formats (ADPCM, etc.). The base I/O register address can be found using the PCI bus for PCI models, or by detecting the presence of an older ISA Sound Blaster by issuing a Get Version command to one of several common I/O port addresses (0x220, 0x240, etc.) and waiting for a response.
To play audio, the ISA DMA controller must be programmed, then the DSP must be issued a Set Output Sample Rate command, and a Play command that includes the format of the audio (mono/stereo, signed, etc.) and a sample count.
Base port for DSP ports is 0x220.
| Offset | Description |
|---|---|
| 0x04 | Mixer Port (Set to 0x82 for Interrupt Status) |
| 0x05 | Mixer Data (Read to get Interrupt Status) |
| 0x06 | DSP Reset |
| 0x0a | DSP Read |
| 0x0c | DSP Write (Read this port for Write Status) |
| 0x0e | DSP Read Status (Read this port to acknowledge 8-bit interrupt) |
| 0x0f | 16-bit Interrupt Acknowledge (Read this port to acknowledge 16-bit interrupt) (DSP Version 4.0+ Only) |
| Command | Description |
|---|---|
| 0x41 | Set Output Sample Rate |
| 0xa6 | Play PCM (Auto Initialize DMA, FIFO Enabled) |
| 0xd9 | Stop PCM (Auto Initialize DMA) |
| 0xe1 | Get DSP Version |
When the samples have been played, an interrupt will be fired, and the OS/Driver will have the chance to refill the buffer, or to issue a Stop command.
Because you only have a single DMA buffer to transfer data, it is recommended that you issue the Play PCM command with a sample count of half of the data buffer. This will fire an interrupt when the buffer is half played, allowing you to refill the segment that was just played, while the DSP continues playing the other half, and so on.
Reading and writing
Until you write to the DSP write port, check the DSP write port is 0x00. Until reading the DSP read port, check the DSP status for 0x80.
Detecting DSP
Detecting DSP is really easy. You must send to DSP reset port 1, wait 3 microseconds, send to DSP reset 0 and read DSP read port. If in it is 0xAA, DSP exist.
Playing sound
- Detect DSP
- Load sound data to memory
- Program ISA DMA
- Set output sample rate
- Write DMA transfer type to DSP
- Write data lenght to DSP(low byte/high byte)
Code
#define DSP_RESET 0x226
#define DSP_READ 0x22A
#define DSP_WRITE 0x22C
#define DSP_BUFFER 0x22A
#define DSP_STATUS 0x22E
#define DSP_INTERRUPT 0x22F
void reset_DSP(void) {
outb(DSP_RESET, 1);
outb(DSP_RESET, 0);
if(read_DSP()==0xAA) {
sound_blaster=TRUE;
}
}
void sb16_init(void) {
reset_DSP();
//if DSP doesnt exist
if(sound_blaster==FALSE) {
return;
}
//get DSP version
write_DSP(0xE1);
sb16_version_major=read_DSP();
sb16_version_minor=read_DSP();
}