gEDA-user: FPGA, uC, and JTAG (was Re: icarus, fork, and recursive tasks)

[Larry Doolittle <ldoolitt@xxxxxxxxxxxxxxx>]

On Mon, Nov 08, 2010 at 05:09:30PM -0500, DJ Delorie wrote:
> > Just boot the FPGA from the processor.  That's what I always do.
> > When I have a processor, that is.  The only overhead is the four
> > GPIO pins attached to the FPGA JTAG, and those can be put to good
> > use after booting as well.
> 
> I used the SPI pins, just streamed the bitstream at full speed.  The
> RX board uses jtag, so I have to convert the bitstream to XSVF and
> play it into the chip, but I don't have to include that code (or
> bitstream) in any normal apps.

I always like the satisfaction of "seeing" the JTAG ID of the chip
before blindly bit-banging a megabyte to a chip that might not really
be there.  I also use JTAG to access registers on the running chip;
it works about as well as SPI in that regard.

  - Larry


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