Teensy debugging via JTAG

[ybk]

I acquired Teensy++ http://www.adafruit.com/products/731 with the intention to use with Atmel AVR Dragon http://store.atmel.com/PartDetail.aspx?q=p:10500053
My project is relatively large and dealing with USB bootloader trial and error method is getting very time consuming.
Having read the AT90USB1286 400+ pages documentation I found that it supports JTAG. However it appears that JTAG is disabled by a proprietary halfkay loader to protect the code. I wonder if there is a documented path to switch from USB loader to hardware debugger/AVR studio.

[adafruit]

you can use the Dragon via ISP to turn the JTAG fuse back on - its not set in the bootloader its set by a fuse

[ybk]

you can use the Dragon via ISP to turn the JTAG fuse back on - its not set in the bootloader its set by a fuse

AVR Dragon is indeed able to communicate with Teensy board in ISP mode.

BODLEVEL = 2V6
HWBE = [X]
OCDEN = [ ]
JTAGEN = [ ]
SPIEN = [X]
WDTON = [ ]
EESAVE = [ ]
BOOTSZ = 512W_FE00
BOOTRST = [ ]
CKDIV8 = [X]
CKOUT = [ ]
SUT_CKSEL = EXTXOSC_8MHZ_XX_16KCK_0MS

EXTENDED = 0xF3 (valid)
HIGH = 0xDF (valid)
LOW = 0x5F (valid)

LB = PROG_VER_DISABLED
BLB0 = NO_LOCK
BLB1 = LPM_SPM_DISABLE

LOCKBIT = 0xCC (valid)

I see that both Memory Lock Bits are programmed and thus pretty much everything is locked unless "Erase Device" operation is performed. Is there an alternative loader? I would like to preserve original functionality.

[adafruit]

the bootloader is not distributed, but you could ask PJRC for help - he might be able to send you a teensy++ with the bits unlocked

[ybk]

the bootloader is not distributed, but you could ask PJRC for help - he might be able to send you a teensy++ with the bits unlocked

I know that PJRC bootloader is not distributed, that is why I included word "alternative" in my original question. I've heard that there is an open source bootloader with the same functionality but I haven't been able to find a ready to use one yet. Any pointers?

Sending with bits unlocked means distributing bootloader which PJRC will not do.

[adafruit]

we do not know of an alternative bootloader

[ybk]

we do not know of an alternative bootloader

After some searching I found LUFA library which includes a bootloader similar to an original one. The only problem is that loaded program starts only after a powercycle. Included in the bootloader reset sequence

Code: Select all

   USB_Detach();

   /* Enable the watchdog and force a timeout to reset the AVR */
   wdt_enable(WDTO_250MS);

   for (;;);

does not work as on author's at90usb1287 device. In the Teensy++2.0 case it appears to restart the bootloader. USB seen detached and then reattached again to the bootloader application.

Is there anything special about WDT here? If I add the same reset code into the PJRC blinky example at the end of while(1) loop it causes LED to blink rapidly instead of a restart of MORSE sequence.