Limits:

• Audio buffer of the Card (on the card / DMA)
• precission of pointer to data on the audio buffer
• Additional Adio buffer on the AD and DAs

  eg. this is sometimes not to small having a extra processor on board like the hammerall-DSP has latency on Multiface and Digiface in Addition to th PCMCIA or PCI-Card.

• PCI Bulk Transfer size

  Since PCI is tranfres data in bulk of data. Eg. this can be on a stereo bases at least 256 Bytes which is on an stereo data each 4bytes/frame = 64 Samples, 512B -> 128Samples, ...

  So CPU never knows how much is actuelly transfered and has to wait that transfer finish which is a minimum of latency card can do.

Examples:

Hammerfall 9652:

• 1 Sample = 1 32Bit-word
• Audio DMA Buffer je Kanal 64...8192 = 1.5ms - 186ms

  bei (44100 Hz) jeweils für Eingangs- und Ausgangsbuffer

• Interrupts: (fragmentsize) 2 for a doublebuffer size.
• PCI Burst: 64 32Bit-words for all channels (in or out)
• Conclusion:
  • using pointer can only be as accurate as PCI-Burst Size
  • using IRQ the buffer size is the limit