Re: gEDA-user: gRX OS board

[DJ Delorie <dj@xxxxxxxxxxx>]

> > Want FreeRTOS?  Or one of these boards?
> 
>    One of those boards.  I run lots of FreeRTOS.  (ARM7, Philips
>    LPC2xxx)

I'll keep that in mind.

> > Other minor peripherals: Consumer IR (tv remote) receiver,
> 
>    Eh...lots of stuff has IR but nothing ever seems to use it. ;)

I had a few pins left over, had to think of *something* to put on
them, and a friend of mine had just asked for help debugging an IR
repeater module...  Hence the ambient light sensor, thermistor, and
IR.

> > For my second RX project, I was thinking of a board with an ethernet
> > switch chip (the RX has MII) and a USB hub chip, plus microsd and
> > sdram.  That gives you a home firewall/appliance/server box with 2Gb
> > of "disk space" and 64 Mb of RAM.
> 
>    This all sounds like lots of fun to me.  Maybe a hair more SDRAM 
> might be nice though.

The chip supports up to 128 Mbyte directly.  The board accepts up to a
64 Mbyte chip (32Mx16bit); You'd need to pair two 64Mx8 chips to fill
the available address space.  The SDRAM (SDR, not DDR) is one of the
most expensive parts of the board; I put only 32Mb on the first one
because it was $25 cheaper than the 64Mb chip.

The sdram controller on the RX is naive, though.  It does a full
ras/cas cycle to read each word, so it takes 5 cycles per read (no
burst).  Combine that with a half-speed external bus (50 MHz) and
you're talking a 10 mhz "read rate" (20 mbyte/sec max throughput, 40
for the 32-bit bus on the BGA version).  The RX chip allows you to
overclock the external bus but I don't know how reliable that would be
with the sdram chip on the same bus as the fpga.

>    I especially like the ability to power-cycle the board without 
> re-enumerating on the USB.  That's good thinking.

Only the FT232R does that.  The native USB still resets.

>    Has anyone done up a nice Forth system for that processor
> architecture?  I might attempt it if I can get a cheap development
> board.  (it'd have to be SUPER cheap the way things are going down
> here lately, though)

If you want to try for the contest, they'll give you an RX-RDK board
free.  No sdram on it though.  Costs $99 otherwise.

How much stuff do you *need* on a "super cheap development board" ?
All you really need to develop RX code is the chip ($18) and an FT232R
($4.50 plus $1 for the connector).  Maybe a 3.3v regulator ($0.50).
Adding SDRAM only costs as much as the sdram chip itself.

I can hook you up with a simulator and development tools if you want
to play with it...


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