Re: [microblaze-uclinux] Minimal mb-system on virtexII

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

Hi Jan-Willem,

Kemna Jan-Willem wrote:
> On my current pcb i use a virtex-II device, currently the xc2v80-4fg256c.

the v80 might be a bit of a squeeze for any microblaze system - how many 
slices does it have?

> The only external component is an AMD-flash memory, currently the am29lv641.

another difficulty, you definitely need external RAM of some kind, 1 meg 
absolute minimum to just boot the kernel, 2meg to even think of doing 
anything useful.

> The communication with the outside world is now only serially via i2c and
> spi, 
> but it should not be too difficult to get a uart connected to it as well.

I think a breadboard with a couple of wires and a max232 chip would be 
sufficient for that.

> I'm wondering if this pcb can be used to start testing with microblaze and
> uclinux ???

I'm sorry, from what you've said it doesn't seem likely :(

> Is the xc2v80 big enough for that or do i have to replace it with a bigger, 
> pincompatible device (if so, which one, xc2v250 or xc2v1000)??

again I'm not sure about fitting a mcroblaze system into a 250... the 
"bare-bones" mbvanilla target uses about 30% of the xc2v1000.  That 
could be trimmed a bit - see below.  You will have no problems with an 
xc2v1000... even room left for the xilinx emac core ;-)

The best bet is to probably grab the mbvanilla_ddr target from the 
website, and start hacking at the MHS (and UCF) files.  Remove one of 
the memory controllers, one of the UARTs, and also the GPIO.  That's 
probably about as small as you can go.  Then synthesise it for different 
devices and see what it can fit into.

> What else am i overlooking/forgetting ???

External ram is a show-stopper.  I think you could _just_ boot uclinux 
in the internal bram on a xc2v8000!!! not very practical!  for mere 
mortals like us, the external ram is essential.

Regards,

John

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