[dorkbotpdx-blabber] Does benito5 only program but not debug AVRs

[Paul Stoffregen]

All my debug stuff is for the NXP/Philips LPC2000 chips, which are based 
on an ARM7 (32 bit) core.  I am using the AT90USB82 chip as a USB to 
JTAG adaptor, but I can only debug 32 bit ARM chips, not Atmel's 8 bit 
AVR chips.

For an analogy, consider using a USB-serial adaptor with an FTDI chip to 
program a bare-bones Arduino.  The adaptor uses a FTDI chip, but it only 
programs the AVR (Arduino) chip, not a FTDI chip.

Most AVR chips have debug wire, which is a closed, proprietary 
protocol.  Some also have JTAG.  While JTAG itself is an open spec, JTAG 
itself only tells you how to access registers inside the chip.  To 
actually use JTAG, additional specs are necessary to know what registers 
are available and how to use them (it's usually quite complicated).  
Atmel has published boundary scan info for some chips (which allows 
manipulating the external pins for testing the circuit board traces), to 
the best of my knowledge, Atmel has never released  JTAG debug register 
specs which would be necessary to use that JTAG port to debug an AVR 
processor.

If those JTAG register specs are available for AVR chips, please tell me 
where.

Without that info, there is no hope of ever making an open debug tool 
for the AVR/Arduino (which is the main reason I'm using the ARM chip).


-Paul


> Paul Stoffregon has done some work towards this using the at90usb82. 
> Debug wire as I understand it is Atmel proprietary.