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Limits:

  • Audio buffer of the Card (on the card / DMA)
  • precisi0on 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:

  • Audio DMA Buffer 64...8192 = 3ms-186ms
  • Interrupts: (fragmentsize) 2 for a doublebuffer size.
  • PCI Burst: 64 (32Bit words) accurate since of this.
  • Conlcusion:
    • using pointer it can be acurate as PCI-Burst Size
    • using IRQ as sync Buffer Size is limit



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