README.md

Setup

1. Install OpenOCD. You need version >= 0.8.0.

• This version is not in Ubuntu 14.04, but the packages from Ubuntu Utopic work fine there
• brew install open-ocd installs >= 0.8.0.

1. Acquire a configuration script for your Bus Blaster. Included in the firmware repo is tools/tessel-busblaster.cfg.

2. Plug the JTAG cable into the Bus Blaster's adapter board and the Tessel. Pin one is towards the USB port; the cable goes over the center of the board.

3. Run

arm-none-eabi-gdb out/Release/tessel-firmware.elf -ex 'target remote | openocd -c "gdb_port pipe;" -f tools/tessel-busblaster.cfg'

(adjust paths as appropriate) to launch gdb.

GDB commands

Basics

• c - continue
• ctrl-c - stop
• p expr - print the value of the C expression expr
• bt - stack backtrace
• s - step instruction, goes into calls
• n - next instruction, skips over calls
• fin - run until return from function
• break function - break at the beginning of a function (can also pass file.c:line)
• delete 1 - delete the first breakpoint
• tbreak - break only once

Hardware

• mon reset - Reset Tessel and all on-chip peripherals (like the reset button)
• mon soft_reset_halt - Reset the CPU only

Other notes

• Make sure your .elf file matches the firmware on the Tessel. Otherwise the position information will be wrong and calls will crash.

• LPC1800 SPIFI Flash is functional from OpenOCD, but I don't recommend using it. Flash Tessel with the bootloader (make arm-deploy) before running GDB.

• The ROM confuses JTAG on reset. If you c and then ctrl-c, it recovers. To debug the very beginning of execution, use

  mon soft_reset_halt
  tbreak main
  c
  

Troubleshooting

OS X: If you are getting a libusb error, you may need to disable some system drivers in order for OpenOCD to work. Run kextstat | grep -i ftdi. If any drivers are listed, you need to run either sudo kextunload -bundle com.apple.driver.AppleUSBFTDI and/or sudo kextunload -bundle com.FTDI.driver.FTDIUSBSerialDriver. For a long-term solution for configuring this, see http://alvarop.com/2014/01/using-busblaster-openocd-on-osx-mavericks/.