HydraFW JTAG guide

HydraFW Bus JTAG (Joint Test Action Group)

Bus: JTAG
Connections: four pins (TMS, TCK, TDI, TDO) and one optional pin (TRST)
Output types: 3.3volt normal output, or open drain
(pull-up/pull-down resistors integrated in MCU or external).
Pull-up resistors: required for open collector output mode (2K – 10K).
Maximum Voltage: 5.5volts (5volt safe).

This guide is updated towards firmware release HydraFW v0.8 Beta: HydraFW (HydraBus) v0.8-beta-0-ga2aab9d 2016-10-13

Protocol configuration syntax description:

• show Show JTAG parameters or show pins Show pins used in this mode

• pull with parameter up or down or floating to choose internal MCU pull up/down or no pull/external

• msb-first or lsb-first to send/receive respectively MSB first or LSB first.

• tck, tms, tdi and tdo with an integer parameter to set the corresponding pin on PB (tms 1 sets TMS on pin PB1)

• brute with bypass or idcode parameters is used to discover JTAG ports on an unknown device.

• bypass to query the number of devices in the JTAG chain.

• idcode to get the devices IDCODEs in the JTAG chain.

• openocd to switch to openOCD mode. See OpenOCD guide

• exit to exit JTAG mode

> jtag
Device: JTAG1
GPIO resistor: floating
Bit order: LSB first

Configuration options:

Hardware Informations:

jtag1> show pins 
TMS: PB10
TCK: PB11
TDI: PB8
TDO: PB9
TRST: PB7

Protocol interaction syntax description:

r or read Read one packet. (r:1…255 for bulk reads)

w or write Followed by values to write byte(s). (w:1…255 for bulk writes)

0 Write this Octal value. Format is prefixed by a 0 (values from 000 to 077)

0b Write this binary value. Format is 0b00000000 for a byte, but partial bytes are also fine: 0b1001.

0x Write this HEX value. Format is 0x01. Partial bytes are fine: 0xA. A-F can be lower-case or capital letters.

0-255 Write this decimal value. Any number not preceded by 0x, or 0b is interpreted as a decimal value.

" Write an ASCII-encoded string

Write support optional repeat : (eg.: 10:1…255 for repeated write of same value 10 in this example)

space Value delimiter. Use a space to separate numbers/commands. Any combination is fine, delimiter is required between each number/command, Example: 0x1 0xff 0 10 0b11 077

^ to send one clock tick

/ to set TCK level high

\ to set TCK level low

- to set TDI level high

_ to set TDI level low

[ to set TMS level high

] to set TMS level low

! to read TDO with clock tick

. to read TDO without clock tick

& Delay 1uS. (&:1…1000000 for multiple delays)

% Delay 1mS. (%:1…1000000 for multiple delays)

~ Write a random byte. (~:10 repeats the same random byte 10 times)

Protocol interaction example usage JTAG1 to discover JTAG pins:

Connect several test pins on the board to analyze on HydraBus PBx pins, and run :

jtag1> brute idcode 12
Bruteforce on 12 pins.
Device found. IDCODE : FC300037
TMS: PB8 TCK: PB9 TDO: PB7

jtag1> brute bypass 12
Bruteforce on 12 pins.
TMS: PB8 TCK: PB9 TDI: PB6 TDO: PB7

Additional informations about JTAG

For more details on JTAG see: https://en.wikipedia.org/wiki/Joint_Test_Action_Group