$ psearch jtag
devel/avarice Atmel AVR JTAG programmer and debugging interface for avr-gdb
devel/stlink STM32 ST-Link JTAG variant tools
devel/urjtag Extended utility to work with JTAG-aware boards
JTAG debugging requires specific hardware to connect to the JTAG ports on the board.
https://en.wikipedia.org/wiki/JTAG
(Seeed Studio BusPirate - GoFlex.net) (GoFlex.net - Seeed Studio BusPirate)
( nc - 1 nc ) ( 10 GND - serial cable GND )
( 6 blue (aux) - 2 IN ) ( 9 RxD - serial cable TxD )
( 8 gray (mosi) - 3 TDI ) ( 8 TxD - serial cable RxD )
( 9 white (cs) - 4 TMS ) ( 7 CN - nc )
( 7 purple (clk) - 5 TCK ) ( 6 DOT - 10 black (miso) )
power on goflex.net, serial, buspirate