[lkml]   [2007]   [Oct]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
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.

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2007-10-01 12:07    [W:0.052 / U:0.240 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site