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    SubjectRe: [PATCH] firewire: adopt read cycle timer ABI from raw1394
    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
    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.

    In short: yes we use it for every packet.

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      Last update: 2007-10-01 12:07    [W:0.022 / U:19.608 seconds]
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