Thanks for your input Tom. I'll look at UHD and stream tags. Regards, Sapna
On Tue, Mar 8, 2011 at 9:08 PM, Tom Rondeau <trondeau1...@gmail.com> wrote: > On Mon, Mar 7, 2011 at 2:26 PM, Sapna Dasarath <sapnadasar...@gmail.com>wrote: > >> Hello, >> >> I am running usrp_transmit_path.py for transmission on one USRP >> and usrp_receive_path.py for reception of signals on another USRP. >> I want to determine the exact arrival time of a packet on the USRP. >> >> I get the message stream which is received from packetutils. >> The code in PacketUtils.py gets a packet from the USRP. >> This is populated from copy_from_usrp_buffer in usrp_source_base.cc. >> I am assuming there is some polling mechanism to invoke >> usrp_basic_rx::read for this. >> I want to track the point where this buffer is populated. The time stamp >> of the packet when it is detected by USRP without any modifications by >> higher layers. >> Can this be done without any changes in Firmware? Any pointers on how to >> proceed will be appreciated. >> >> Thanks. >> > > It sounds like you don't want to go this route, but the best thing to do is > start using the UHD and stream tags. There is an interface in the UHD source > block to send stream tags of the sample times. The UHD tags frames with a > time stamp based on the internal clock of the FPGA (which you can tell to > reset). The tags are then passed downstream for you to collect later and > associate a time value with a particular sample. > > The legacy USRP2 interface also allows you to collect the time out of the > metadata, but you will have to dig into the libusrp2 library code to get > access to it. > > If you want accurate time stamps for a USRP1, there really isn't one. You > would have to have a differential timer. Look at clock_gettime for getting > clock information that you might use. > > Tom > >
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