[uCsimm] RE: [uClinux-dev] BEWARE: Lineo 68360 board

From: Michael Leslie (mleslie@lineo.ca)
Date: Wed Nov 22 2000 - 13:13:36 EST


Luc,

It's not quite true that you cannot configure the 68en360 for more than
two Ethernet ports. You can do so, but you are limited, as you observe, to
an aggregate throughput of about 20Mbps.

I would refer anyone interested in the gory details to the 360 manual,
appendix A: "Serial Performance":

  http://www.mot.com/netcomm/aesop/683XX/360/360UM-P3.pdf

and also the "CPM Performance Spreadsheet" and accompanying documentation at:

  http://www.mot.com/SPS/RISC/netcomm/tools/index.html#68360_table

As an example, a router with multiple ethernet connections to 2Mbps DSL
modems, would be well within the limits. From Motorola's worksheet, the
following configuration yields ~73% CPM usage for a 25MHz part:

        Ethernet on SCC1, 10Mbps throughput
        Ethernet on SCC2, 3, and 4, 2Mbps throughput

The perormance of the CPU core should, in an application like a router,
have little to no effect on the throughput of the communications
engine. As long as CPM interrupts are serviced quickly, and the amount of
buffer copying is kept to a minimum, fully loading the CPU should have no
effect on data transfers. This is the basic idea behind the '360, of
course. If the CPU core is performing significant manipulation of the
rx/tx data, then of course it will become a bottleneck. But then a 25MHz
68k core is no DSP...

Cheers,
Michael Leslie,
Lineo Inc.

On Wed, 22 Nov 2000, Paugam Luc wrote:

>
> BEWARE If you use a 25MHz Motorola MC68EN360, you cannot have 3 Ethernet
> ports due to the bandwidth between the CPU core and its CPM (Communications
> Processor Module). It is about 22 Mbits/s.
> You better should use a 33MHz chip: the bandwidth between the CPU core and
> its CPM is 30 Mbits/s (OK for 3 LAN/WAN ports).
>
> Generally it is not a good idea to design a CPU with more than 1 Ethernet
> port, with only a MC68EN360.
> This uP is not very fast: at 33MHz, 6 MIPS, 10500 dhrystones/second (5.5
> BogoMips on uClinux). You have not enough power to fill up 2 or 3 LAN/WAN
> ports and to execute apllications.
>
> In order to remedy this fact and to really use 2 or 3 LAN/WAN ports, you
> need to use your MC68EN360 at 33MHz in companion mode with a MC68EC060 at
> 66MHz.
>
> Best Regards
> Luc
>
> >Michael Leslie [SMTP:mleslie@lineo.ca] wrote:
> >
> >For those interested in Lineo's MC68360 board.
> >
> >The device is designed to be a high-end T1/E1 router platform.
> >For availability and pricing, please contact Jim Stewart
> <jim.stewart@lineo.com>
> >
> >Again, this board's vital statistics are:
> >
> > - 25MHz Motorola MC68EN360
> > - 32M DRAM
> > - 8M FLASH
> > - 10-base-T Ethernet
> > - Serial console
> > - 3 highly configurable WAN ports
> > - IDE interface
> > - Nice and small; designed to mount on a laptop hard disk
> >
> >
> >Cheers,
> >Michael Leslie,
> >Lineo Inc.
>

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