[c-nsp] tag-switching mtu question

[David Freedman]

Gert Doering wrote:
> Hi,
> 
> On Mon, Jun 26, 2006 at 05:09:58PM +0100, David Freedman wrote:
>> 1. Both the PA-FE and IO-FE series of interfaces are limited to
>> transmitting up to 1530 bytes of frame "on the wire"
> 
> I assume that this is a hardware issue of the DEC21140 chips?
> 
> What about the PA-2FE-TX and IO-2FE ethernets, built on the i82543 chips?
> 
> Is IOS clueful enough to do "the right thing" on DEC and i82543 chips
> (if there is a difference)?


Well, the closest thing I can find in terms of documentation on the DEC 
chip is from a VxWorks manual, and it says:

SYSTEM RESOURCE USAGE:
    - one mutual exclusion semaphore
    - one interrupt vector
    - 16 bytes in the uninitialized data section (bss)
    - 180 bytes (plus overhead) of malloc ed memory per unit
    - 1530 bytes (plus overhead) of malloc ed memory per frame buffer, 

    - minimum 5 frame buffers.


This would tend to imply that the 1530B limit is indeed down to the DEC 
chip.

As for the i82543 I can't seem to find any information on this


> 
> (Is there a way to tell IOS "hey, I am using this PA-2FE-TX board because
> I need larger MTUs, but I'm not going to use the second FE port, so please
> shut up and don't annoy me with needless bandwidth points warnings"?)
> 
> gert
>