Paul Koning wrote: > > I wonder if people have examined the worst case timing properties of > PCI... assuming it has any. Lots of buses have no reasonable or > defined worst case behavior. > > paul Typical 33 MHz PCI hardware latencies are 10-20 uSec according to an IBM datasheet. Add to this any delays caused by the 'readPCI' code running on the CPU before and after the read. The PCI 2.1 Specification has two equations for calculating bus latencies after a device wins arbitration of the bus: worst case: latency (bus clocks) = 16 + 8*(n-1) n = number of 32 bit words transferred bus clocks = 1/33 MHz or 1/66 MHz depending on your PCI bus speed. typical case: latency (bus clocks) = 8 + 8*(n-1) The arbitration latency is: m * Latency Timer m = number of masters ( max is 8 ) Latency Timer = typical is 22 bus clocks Your total PCI bus delay is the sum of the two latencies. - Each device can have a different timer setting. Check the settings of your devices. - Some devices can do an endless data transfer without a timer. - Normal Linux can start a PCI data transfer that can run into a real time Linux interval. Experiment with your system setup. If you need shorter delays stop any unnecessary Linux PCI transfers, and plan the transfers better. The PCI 2.1 Specification is available for download at: http://akulin.npi.msu.su/docs/standard/pci21.pdf Latencies are covered in section 3.5. - Kal. --- [rtl] --- To unsubscribe: echo "unsubscribe rtl" | mail [EMAIL PROTECTED] OR echo "unsubscribe rtl <Your_email>" | mail [EMAIL PROTECTED] ---- For more information on Real-Time Linux see: http://www.rtlinux.org/~rtlinux/
