Messages in this thread | | | Date | Mon, 1 Oct 2007 12:03:23 -0400 | From | "Kristian Høgsberg" <> | Subject | Re: [PATCH] firewire: adopt read cycle timer ABI from raw1394 |
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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/
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