Ethernet throughput in OMAP3503 with an external MAC

Hi everyone,

I am also looking for similar information. The Linux PSP document of OMAP describes testing up to 44Mbps on OMAP 35xx processor. However, it does show the CPU loading nor why the speed is limited to 44Mbps (i.e. bound by CPU load, or packets handling logic or GPMC speed).

Does anyone have more information (besides the info provided by the Linux PSP driver documentation) in this area?

Thanks in advance

Chi Ho

I just tested this with an out of the box Angstrom build on an OMAP3 connected to a LAN9221 Ethernet chip using GPMC. Running "iperf" against a standard PC Linux server gave a transmit through put of ~95Mbit/s and a receive throughput of ~70Mbit/s. The transmit and receive tests were conducted individually of each other. I unfortunately didn't check the CPU load during the tests, but I don't believe it to be maxed out in any way.

With respect to the the EMAC in AM3505 I see no reasons it should perform (significantly) differently from this, although I haven't checked it in function - Just gave the datasheet a quick overview. The bandwidths of the GPMC (connecting to external LAN9221) and the internal L3-bus (connecting the internal EMAC in AM3505) are both much larger than 100Mbit/s, so the Ethernet link will be the limiting factor in both circumstances...

I hope this answer helped you forward?
  Søren

Thanks Soren! I'm thinking to test the networking throughput by reducing the CPU clock, and find out the CPU load for ethernet.

What about just running "top" while doing the test with "iperf"?

I just forgot to do it today while testing
  Søren

Thank you for your response. Your answer definitely help us getting a view of the performance.

We tested using OMAP 3503 (embedded module Gumstix) and reached 50Mbps at 100% CPU load. Which processor were you using?

I think the OMAP 3503 does not have an EMAC on-chip. As you said, It is connected to LAN9221 which has both MAC and PHY integrated.

We are also using Angstrom build. Are you using the standard Ethernet driver included in the build?

Thanks

Chi Ho

 

 

Soren, could you please try to measure the CPU usage when you get 70Mbps ethernet performance? Chi Ho only gets 40Mbps using Gumstix. Are you using Mistral board? If yes, could you please provide me the software project files you used to test ethernet. so we can try to reproduce it? Thanks, John

Hi,

Sorry for first getting back to you now, but last week was rather crazy :-) I used an OMAP3503 (or OMAP3530) I can't remember, but it doesn't do any difference since from the Cortex-A8/GPMC point of view they are identical. [:)]

After my previous post, I upgraded to a newer version of U-boot (with NET support enabled) and I can confirm, that my numbers as well went down to around 40-50Mb/s. The reason for this is, that enabling NET support in u-boot will setup of the GPMC CS6 (connected to the LAN9221-chip), to a very slow speed. My initial measurements were done with default timings for CS6. The big questions is now, if they violate the LAN9221 spec (but works anyway) or if the timings in the new U-boot are way too slow. I haven't had time to look into that, but giving it a brief check last week I think the U-boot timings are way too slow.

With respect to the 100% CPU usage while running iperf, the time is consumed by the iperf application itself, and not the LAN9221 driver leaving me to think, that the iperf application just loops in a while-forever-loop while doing the test, but I haven't checked this either. But for now I don't trust this number. For another measurement without too much overhead try transferring some big files (to (/dev/null) using i.e. FTP instead...

Hope this answers your questions - Good luck
  Søren

Soren,

Could you please share this LAN 9221 driver that you're using? I'm getting very low data transfer speeds with the driver I got along with 3530 EVM. (OMAP35x-PSP-SDK-02.01.03.11)

Thanks