Messages in this thread | | | Date | Mon, 01 Oct 2007 11:31:51 +0200 | From | Pieter Palmers <> | Subject | Re: [PATCH] firewire: adopt read cycle timer ABI from raw1394 |
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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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