Re: gEDA-user: gTag Status

[Stephen Williams <steve@icarus.com>]

wwashington@austin.rr.com said:
> What's the latest status on the JTAG project? 

Also, by the way, I got my copy of the IEEE1149 standard the other day,
so I should be able to start working out the ucontroller software, and
I got a USB card so I can look into doing drivers for it.

If Stefan chooses an EEPROM to use, then I can look into writing code
to program it from within the uController. One thing we are missing is
a way to *explicitly* disable to EEPROM so that we can force the micro
to boot up without it.

The way the processor works, it tries to read from the EEPROM on reset.
If it finds a magic code in the beginning, it reads the rest of the
device and uses that to initialize program memory. If it does *not*
find that magic code, then it ignores the EEPROM and the USB interface
kicks into fail-safe mode without the micro, ready to download a program.

This behavior will allow us to program the EEPROM from the micro, and
if the EEPROM can be explicitly be disabled,  broken programs can be
skipped, fail-safe mode entered, and we can reprogram the EEPROM. It
is fairly important, I think. There is no reason to not support a
surface mount EEPROM, soldered on. Why waste pennies on a socket?-)
-- 
Steve Williams                "The woods are lovely, dark and deep.
steve@icarus.com              But I have promises to keep,
steve@picturel.com            and lines to code before I sleep,
http://www.picturel.com       And lines to code before I sleep."