Re: gEDA-user: mcu to sdram interface project

[DJ Delorie <dj@xxxxxxxxxxx>]

> One other nice thing is that the DIN/CCLK pins of the FPGA become
> user I/O after configuration, so when you're done loading the
> bitstream the MCU can use those pins to talk to the FPGA code you
> just installed. My design has a SPI slave port on those pins so I
> can monitor/control with the same SPI port I used to load it
> up. Good for flexibility so I don't have to resynthesize just to
> tweak parameters in the hardware.

The MCU is going to have a full address/data bus going to the fpga, I
don't think I need SPI *also* :-) In theory I can just map a small
part of the address space to whatever config registers I need.

> Ethernet would be pretty nifty. A bit outside my comfort zone right
> now, but it would speed things up a lot.

I've been adding the ENC28J60 part to most of my designs; it's a plain
SPI interface and common enough to be well supported.  I have a uIP
module for it for R8C if anyone needs it.  To add it, you only need
that chip, a pulsejack, a 25MHz crystal, and a few discretes.

Here's a "worst case scenario" with differing Vcc's, leds, etc:

http://www.delorie.com/electronics/powermeter/ethernet.sch

Here's a version when the Vcc's match:

http://www.delorie.com/electronics/alarmclock/ethernet.sch

Note that I've never used the interrupt pin.


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