New subject: Transmitting pkts out of Giga ports

30 Mar 2004

      Chompi,

I think I can answer some of these questions for you.  I believe your
intuition is correct and the transmit code is not filling the MAC
buffers fast enough.  The transmit code for this chapter was not tested
on the gigabit ports, so it's no surprise that the code is not fast
enough.  

However, the IXF1002 has a 2048 byte buffer per port.  So, you should be
able to send Ethernet packets of that size or less without underflowing.
The trick is to set the "tx send threshold" to something large.  This
threshold is the number of bytes that must be in the buffer before the
MAC starts transmitting.  If this threshold is set large enough, you
should never underflow.  This setting can be adjusted in the simulator,
and it can also be adjusted on the hardware using the IXF1002 driver.
If you are on Linux, this is done from user space via IOCTLs.  If you
are on VxWorks, this is done through function calls.

There are also two known bugs in the transmit code that we are trying to
put up on the errata web page.  This may be impacting your ability to
run the code on the hardware.  I have pasted the errata below.  It
should be up on the website soon.

For your last question, unfortunately, I couldn't find any microC code
for transmitting on gigabit ports, but that doesn't mean it doesn't
exist.  Maybe someone else on the list has something like that.

Aaron

Errata:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Page:   N/A
Location:  CD-ROM, Chapter09\transmit.c 
Description: 

The transmit code supplied in Chapter 9 does not properly handle packets
larger than 64 bytes.  There are two corrections:

First, lines 169 and 170 should read:

        port_state.current_data_ptr = 
            (void*)((unsigned int)(port_state.current_data_ptr) + (64 /
sizeof(long long)));

instead of:

        port_state.current_data_ptr = 
            (void*)((unsigned int)(port_state.current_data_ptr) + 64);

This correction accounts for the quad-word addressing of SDRAM on the
IXP1200.

The second correction is to add the following line after line 167:

        mpacket->eop = 0;

This ensures the the per-mpacket state maintained by the fill threads
gets properly initialized for each new packet.

------------------------------ 
Aaron Kunze 
Intel Research and Development 
aaron.kunze@intel.com 
----PGP Key ID: 0x81124B7C---- 
----NOT SPEAKING FOR INTEL---- 
---------GO BOILERS!!---------
...
-----Original Message-----
From: ixp1200-bounces@lists.cs.princeton.edu 
[mailto:ixp1200-bounces@lists.cs.princeton.edu] On Behalf Of 
chompi@softhome.net
Sent: Tuesday, March 30, 2004 4:04 AM
To: ixp1200@lists.cs.princeton.edu
Subject: [ixp1200] Transmitting pkts out of Giga ports
Hi all,
I've recently tried sample code from chap9 Johnson and Kunze 
book and in 
DWB, the code works fine with Fast Eth ports. However, if I 
try to use GE 
ports, it only works when MTU<=192 (<=3 Mpkts per pkt). If 
there are >3 
Mpkts/pkt, the simulation halts with error "Transmit buffer 
underflow". Does 
this mean that the code is not filling up TFIFO fast enough?
Anyways, even if I set MTU<=192, I still cannot send out any 
traffic on real 
hardware (we are using ENP-2506). L3Fwdr reference design 
works fine on the 
board so I do not expect any hardware or configuration problems.
Did anybody encounter this issue before? Is there any sample 
code (in micro 
C) lying around that transmits data over GE ports?
Any help is appreciated.
Chompi. 
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RE: [ixp1200] Transmitting pkts out of Giga ports

Kunze, Aaron

Chompi

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