I am working on a low latency application, sending udp packets from a master to a slave. The master acts as access point sending the data directly to the slave. Mostly it is working well but sometimes data is arriving late in the slave. In order to narrow down the possible sources of the delay I want to timestamp the packets when they are sent out in the master device.
To achieve that I need a hook where I can take a timestamp right after a packet is sent out.
According to http://www.xml.com/ldd/chapter/book/ch14.html#t7 there should be an interrupt after a packet is sent out but I can't really find where the tx interrupt is serviced.
This is the driver: drivers/net/wireless/bcmdhd/dhd_linux.c
I call dhd_start_xmit(..) from another driver to send out my packet. dhd_start_xmit(..) calls dhd_sendpkt(..) and then dhd_bus_txdata(..) (in bcmdhd/dhdpcie.c) is called where the data is queued. Thats basically where I lose track of what happens after the queue is scheduled in dhd_bus_schedule_queue(..).
Does someone know what happens right after a packet is physically sent out in this particular driver and maybe can point me to the piece of code.
Of course any other advice how to tackle the problem is also welcome.
Thanks
The packet is freed in the function
static void BCMFASTPATH
dhd_prot_txstatus_process(dhd_pub_t *dhd, void * buf, uint16 msglen)
in the file dhd_msgbuf.c
with
PKTFREE(dhd->osh, pkt, TRUE);