Re: [microblaze-uclinux] back on the air!

[John Williams <jwilliams@itee.uq.edu.au>]

Hi Michael,

I hope it's OK I've bounced this back to the list, it may be of interest 
to others.

Michael J. Wirthlin wrote:
> I am new to the mailing list and would like to start playing with the
> microblaze uClinux port. Which insight board do you recommend for this
> port?

The initial port was undertaken on the Insight/Memec Virtex2 System 
Board, V2MB1000.  I think they are about $US900 or thereabouts, 
including a Xilinx EDK license.  It has 1MB RAM, 8MB flash, and 32MB DDR 
DRAM, USB, ethernet, serial ( x 2), PS-2 connectors/physical drivers, 
plus a bunch of unconstrained user IO.

It should be trivial to "port the port" over to a new board though, 
since currently all system peripherals are just OPB cores (or wired 
outputs from the same, like uartlites and memory controllers etc).  It 
would mostly be a case of modifying the UCF file.

I haven't worked out a minimum spec of boards to host 
microblaze/uclinux, but here are a few thoughts on the subject:

Based on other uClinux ports and what I'm seeing so far, you can easily 
bring a 2.4.x kernel up in about 1MB RAM, launch a shell, some simple 
utilities, a small file system, and that's about it.

Not much more useful stuff will fit into 1MB (the base kernel size is 
about 450K).  You can get tricky and do things like XIP (execute in 
place) running application and kernel code directly from the image 
stored on the filesystem in flash.  There is support in uClinux for all 
that, but it hasn't been ported yet.  Currently the entire kernel and 
file system image get copied into RAM and it all runs from there.

As for peripherals (or at least, external connectors), that's up to you. 
  For us, ethernet driver support is a high priority, plus USB and a few 
others.  The Memec board I mentioned has physical interface chips for 
these, and we will eventually wrap linux device drivers around existing 
cores (from Xilinx and others).

I think Xilinx have started this process as part of the "official" 
Montavista Linux port for the PPC V2Pro devices.  I think it's all GPL 
so we plan to use it as much as possible, and just drop it in to the 
uClinux side of things.

So, if I were looking into a new board to eventually do some real 
uClinux work on, I'd look for at least 8MB of RAM, but up to 32MB if 
possible, ethernet PHY (or even an external MAC chipset maybe - the 
ethernet MAC core consumes about 60% of a XC2V1K device!), plus any 
other app-specific hardware you might be interested in.  A serial port 
is a very cheap and useful thing to have while debugging!

We'll be sticking with the Insight boards until we are ready to spin our 
own hardware, which should be around the last quarter of this year if 
not sooner.

Cheers,

John