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