lkml.org 
[lkml]   [2007]   [Oct]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH] firewire: adopt read cycle timer ABI from raw1394
    On 10/1/07, Pieter Palmers <pieterp@joow.be> wrote:
    > Stefan Richter wrote:
    > >> This duplicates the read cycle timer feature of raw1394 (added in Linux
    > >> 2.6.21) in firewire-core's userspace ABI.
    > >
    > > Kristian and Pieter, does this simple duplication of the ioctl make
    > > sense on its own? AFAIU rawiso's iso packet buffers look different from
    > > fw-cdevs's. It seems to me as if rawiso always put the cycle into a user
    > > buffer for each iso packet received...
    > >
    > > raw1394.h::struct raw1394_iso_packet_info {
    > > __u32 offset;
    > > __u16 len;
    > > __u16 cycle; /* recv only */
    > > __u8 channel; /* recv only */
    > > __u8 tag;
    > > __u8 sy;
    > > };
    > >
    > > raw1394.c::raw1394_iso_recv_packets()
    > >
    > > /* copy the packet_infos out */
    > > for (i = 0; i < upackets.n_packets; i++) {
    > > if (__copy_to_user(&upackets.infos[i],
    > > &fi->iso_handle->infos[packet],
    > > sizeof(struct raw1394_iso_packet_info)))
    > > return -EFAULT;
    > >
    > > packet = (packet + 1) % fi->iso_handle->buf_packets;
    > > }
    > >
    > > ...while the Juju ABI returns the cycle only for those packets whose
    > > fw_cdev_iso_packet.control had the FW_CDEV_ISO_INTERRUPT flag set.
    > > The cycle is then written out in the fw_cdev_event_iso_interrupt event
    > > which happens when this particular packet was received. Right?
    > >
    > > Pieter, do applications like yours need the cycle counter only for a few
    > > predetermined packets or for each and every packet?
    >
    > We need it for every packet for two reasons:
    > 1) it's the only way to determine how many packets were dropped when
    > packet drops are flagged in the callback

    Your application should know what the timestamp should be for each iso
    receive callback and if you see a larger value than expected you can
    use that to calculate how many cycles were lost.

    > 2) we convert the 16-bit SYT timestamp of a packet to a full 32-bit
    > cycle counter value. This because the range of the 16-bit SYT is too
    > small (only 16 packets) for systems that have large buffering.

    If you get the timestamp for the first packet in a receive batch, you
    can still do this, right?

    cheers,
    Kristian
    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2007-10-01 18:05    [W:0.025 / U:0.112 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site