# Re: Issues with syncing two USRPs! (Discuss-gnuradio Digest, Vol 139, Issue 12) **URL:** \ **Category:** GNU Radio\ **Created:** [June 14, 2014, 2:21am UTC](https://www.ruby-forum.com/t/re-issues-with-syncing-two-usrps-discuss-gnuradio-digest-vol-139-issue-12/230374 "2014-06-14T02:21:17Z")\ **Posts on this page:** 1\ **Page:** 1
**Author:** ![jason\_sam](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/7993a0/32.png) [@jason\_sam](https://www.ruby-forum.com/u/jason_sam)\ **Post date:** [June 14, 2014, 2:21am UTC](https://www.ruby-forum.com/t/re-issues-with-syncing-two-usrps-discuss-gnuradio-digest-vol-139-issue-12/230374/1 "2014-06-14T02:21:17Z")
Hi Martin, This is a follow up on my earlier email. I am still having issues with getting two N200’s to work together. First, please find a short answer to your questions. > > Out of curiousity, do you have a MIMO cable and are willing to test that? > > No, I do not have a MIMO cable. > > You’re saying you get 2 channels per LFRX, correct? Also, are you > > attenuating the signal? > > Yes, I tried both 2 (i.e., A:A, A:B) and 1 (i.e, A:AB). The signal is > > attenuated by a factor of four 'cuz I’m using two T’s each with two > > outputs. > > Just to confirm: You’re setting _both_ clock and time sources to > > external? > > Yes. I initially thought the issue has to do with syncing, but it seems that it is not due to syncing per se (?!) A quick recap. One N200 acts as a single-channel Tx (i.e., A:AB) and a two-channel Rx (i.e., A:A and A:B). The other N200 only acts as a two-channel Rx (i.e., A:A and A:B). I am using two T’s to split my Tx signal into four signals and I am feeding those to the Rx’s. [i.e., my Rx signal is attenuated by a factor of 4]. In GRC, I always use an USRP sink that is properly configured for the Tx AB channel. At the Rx side, for the sake of testing, I tried multiple configurations as follows. First, I only considered one N200 (i.e., a single motherboard) at a time, and I used a source as above. When I do so, _either I apply external sync and clock or not_, I am able to perfectly receive my signal. This test was successful when I fed-in the source with either the two Rx channels from the first or the second N200, separately. Second, I used one single source with two motherboards and four Rx channels. I tested this\* with and without sync/clocking signals\*. In both cases, I get this error message: > Using Volk machine: sse4\_a\_64\_orc > _thread[thread-per-block[4]: \]: > RuntimeError: fifo ctrl timed out looking for acks_ Please note that, despite this message, the GRC program looks as if it is running, and the GUI shows me the output from the scope (i.e., scope is just placed before the USRP Tx sink). However, the output from the scopes after the Rx USRP is null for the four channels. [For Rx’s with a single source, I also tried a single-channel from the two motherboards (i.e., A:AB) without any success]. Checking the system monitor on my computer confirms that one USRP is transmitting all the time while no receive/incoming traffic whatsoever. Besides this, I tried various diagnostics. I thought that the issue may has to do with the Ethernet controller/card on my computer, and that it may be dropping/delaying some packets. Hence, I ‘unmanaged’ the Ethernet connections, and I applied static configuration. I also tried to disable some options in the network driver such as autoneg, adaptive, coalesce, etc., without any success. Please find below some diagnoses that may give some clues on the FIFO ACK error, T-UD2H:~$ sudo ethtool --show-coalesce eth4 Coalesce parameters for eth4: Adaptive RX: off TX: off stats-block-usecs: 0 sample-interval: 0 pkt-rate-low: 0 pkt-rate-high: 0 rx-usecs: 20 rx-frames: 5 rx-usecs-irq: 0 rx-frames-irq: 5 tx-usecs: 72 tx-frames: 53 tx-usecs-irq: 0 tx-frames-irq: 5 rx-usecs-low: 0 rx-frame-low: 0 tx-usecs-low: 0 tx-frame-low: 0 rx-usecs-high: 0 rx-frame-high: 0 tx-usecs-high: 0 tx-frame-high: 0 T-UD2H:/etc/network$ sudo ethtool --show-coalesce eth3 Coalesce parameters for eth3: Adaptive RX: off TX: off stats-block-usecs: 0 sample-interval: 0 pkt-rate-low: 0 pkt-rate-high: 0 rx-usecs: 20 rx-frames: 5 rx-usecs-irq: 0 rx-frames-irq: 5 tx-usecs: 72 tx-frames: 53 tx-usecs-irq: 0 tx-frames-irq: 5 rx-usecs-low: 0 rx-frame-low: 0 tx-usecs-low: 0 tx-frame-low: 0 rx-usecs-high: 0 rx-frame-high: 0 tx-usecs-high: 0 tx-frame-high: 0 T-UD2H:/etc/network$ ifconfig -a eth4 eth4 Link encap:Ethernet HWaddr REMOVED inet addr:192.168.10.1 Bcast:192.168.10.255 Mask:255.255.255.0 inet6 addr: REMOVED\_by\_KE Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:118227 errors:0 dropped:0 overruns:0 frame:0 TX packets:733915 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:8366882 (8.3 MB) TX bytes:930252111 (930.2 MB) Interrupt:19 GA-MA785GMT-UD2H:/etc/network$ ifconfig -a eth3 eth3 Link encap:Ethernet HWaddr REMOVED inet addr:192.168.20.1 Bcast:192.168.20.255 Mask:255.255.255.0 inet6 addr: REMOVED\_by\_KE Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:40807 errors:0 dropped:0 overruns:0 frame:0 TX packets:11811 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:3100954 (3.1 MB) TX bytes:1076135 (1.0 MB) Interrupt:18 We also sucessfuly upgraded the firmware for both the USRPs. We noticed that (i.e., also shown form the stickers on the back of each device) one N200 is rev 2.0 and the other is rev 4.0. Could that be the cause of the problem? I will appreciate any help on fixing this issue. Thank you in advance. Khalid