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cogansco
Adventurer
Adventurer
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Registered: ‎07-28-2015

Zynq 7020: How to offload xil_printf to second processor core?

Hello,

Setup: I am trying to develop a TCP/IP application, I originally based it on the lwIP Echo Server example.  Hardware is Arty Z7 board with Zynq 7020.  I have modified the application to regularly stream chunks of data 1000 times per second.  Each chunk of data is ~100 bytes, so total bandwidth is low - about 100 kB/sec. 

Problem: However, I notice regular interruptions in the stream - sometimes as short as 50 msec, and sometimes up to 300 msec.  I am currently running on just 1 processor (core_0), and I notice that these gaps happen when the tcp_sndbuf is full.  It seems tcp_write requests are queueing up and run out of space.  Eventually, the stream of data will continue, but in the meantime some data has been lost/never sent.  The problem can be reliably triggered when calling xil_printf.  This function seems to take a long time to execute, maybe because JTAG over the USB is slow?

Question:  It seems like the xil_printf statements take priority away from TCP/IP traffic somehow, is this true?  Should I try to get a second application running on a second core, and have my second core handle the xil_printf?  I hope this is not necessary though.  Is there some other way to force the TCP traffic to have priority so that other processes don't cause it to drop data?

I wonder if my problem is similar to the one described here:

https://forums.xilinx.com/t5/Ethernet/LWIP-transmit-stalls-on-Zynq-Ultrascale/m-p/1085557

 

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maps-mpls
Mentor
Mentor
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Registered: ‎06-20-2017

Things to think about:  What is it you're printing?  And to where (UART)?  Why?  Could you use sprintf into a buffer instead, and then dump the buffer at some other time?  Are they just debug prints, or something that is essential?  If you're using a UART, did you set it up to be interrupt driven?  Could you use something like proto threads (same author as lwIP)?    What OS are you using?

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