https://github.com/cyphunk/jtagenum

Given an Arduino compatible microcontroller or Raspberry PI (experimental), JTAGenum scans pins[] for basic JTAG functionality and can be used to enumerate the Instruction Register for undocumented instructions. Props to JTAG scanner and Arduinull which came before JTAGenum and forwhich much of the code and logic is based on. Feel free to branch and modify religiously (readme, credits, whatever)
https://github.com/cyphunk/jtagenum

arduino jtag raspberrypi

Last synced: about 2 months ago
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Given an Arduino compatible microcontroller or Raspberry PI (experimental), JTAGenum scans pins[] for basic JTAG functionality and can be used to enumerate the Instruction Register for undocumented instructions. Props to JTAG scanner and Arduinull which came before JTAGenum and forwhich much of the code and logic is based on. Feel free to branch and modify religiously (readme, credits, whatever)

• Host: GitHub
• URL: https://github.com/cyphunk/jtagenum
• Owner: cyphunk
• Created: 2010-04-15T21:11:25.000Z (over 14 years ago)
• Default Branch: master
• Last Pushed: 2023-10-30T08:40:07.000Z (11 months ago)
• Last Synced: 2024-07-31T23:46:05.968Z (about 2 months ago)
• Topics: arduino, jtag, raspberrypi
• Language: C++
• Homepage: http://deadhacker.com/tools
• Size: 138 KB
• Stars: 695
• Watchers: 41
• Forks: 101
• Open Issues: 11
• Metadata Files:
  • Readme: README.md

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README

        
About JTAGenum

==============

JTAGenum is an open source Arduino ``JTAGenum.ino`` or RaspbberyPi 

``JTAGenum.sh`` (experimental) scanner. This code was built with three primary 

goals:

1. Given a large set of pins on a device determine which are JTAG lines

2. Enumerate the Instruction Register to find undocumented functionality

3. be easy to build and apply

JTAGenum is a more Arduino'y fork of 

[Arduinull](https://github.com/zoobab/arduinull) by Sébastien Bourdeauducq 

(lekernel), which is inspired by Benedikt Heinz's 

[JTAG scanner](https://elinux.org/JTAG_Finder).

JTAGenum also includes instruction scanning functionality best described

by Felix Domke (tmbinc) in his 

[26c3 paper](http://events.ccc.de/congress/2009/Fahrplan/attachments/1435_JTAG.pdf).

The initial version of this branch was built for personal research and while

working on various projects at [Recurity Labs](https://recurity-labs.com/).

Please feel free to contact me with any questions, problems, targets or

updates. I would be more than happy if you fork and take the code in

whatever direction you choose.

Links

=====

* Embedded Analysis wiki: http://github.com/cyphunk/JTAGenum/wiki

* JTAGenum blog post: http://deadhacker.com/2010/02/03/jtag-enumeration/

* JTAGenum video tutorial "Ghetto Tools for Embedded Analysis REcon 2011":

  https://www.youtube.com/watch?v=ZmBfahwV3ss

Authors and code branches

=========================

* cyphunk  http://github.com/cyphunk/JTAGenum/

* jal2     http://github.com/jal2/JTAGenum/

* zoobab   http://hackerspace.be/JTAG_pinout_detector

* z1Y2x    https://github.com/z1Y2x/JTAGenum/

Similar tools or branches:

* gremwell's https://github.com/gremwell/go-jtagenum (RaspberryPi go rewrite + improvements)

* joegrands's http://www.grandideastudio.com/jtagulator/ (purpose built hardware with improvements and added voltage range)

* szymonh's https://github.com/szymonh/SWDscan (arduino based SWD finder)

* szymonh's https://github.com/szymonh/JTAGscan (arduino based with logic similar to jtagulator) 

* dxa4481's https://github.com/dxa4481/inputProtectionShield (1.8-5v voltage shifting shield)

* dipusone's https://github.com/dipusone/inputShieldProtection (fork of dxa4481's shield)

* commercial products MiracleBox, JTAGfinder, EasyJtag (GUI based, some limitations) 

Hardware

========

JTAGenum has been tested on the following hardware:

* RaspberryPi (3.3V) with mixed results

* standard Arduino (5V)

* Arduino on Teensy (3.3V) (http://www.pjrc.com/teensy/index.html)

* Arduino on Texas Instruments Tiva C / Stellaris (3.3V) (https://github.com/cyphunk/JTAGenum/issues/4)

* Arduino on STM32 Bluepill board (3.3V) (https://wiki.stm32duino.com/index.php?title=Blue_Pill and http://www.zoobab.com/bluepill-arduinoide)

When picking your micro-controller platform consider two issues: 

1. How many pins do you want to check on your target. 

2. what voltage level does your target device require.  

Concerning voltage RaspberryPi's I/O operate at 3.3v, many Arduinos 

work at 5 volts. Some are switchable but even those that are not could 

be modified. Alternatively voltage shifting Arduino shields or 

voltage shifting gadgets can be used. See the Voltage Shifting Appendix 

discussion on the Embedded Analysis wiki for more details.

https://github.com/cyphunk/JTAGenum/wiki/Embedded-Analysis#Voltage_Shifting

When connecting the micro-controller to the pins of your target one

thing to be aware of is possible cross-talk between wires. The 

loopback check function in JTAGenum cab help you determine which wires

may produce cross talk. 

Usage

=====

For use on **Raspberry Pi** use and consult the ``JTAGenum.sh``. The 

Raspberry Pi pins being used for scanning should be specified inside the script

file. This script is experimental and only provides the functions for finding JTAG. 

To use the script should be *sourc'ed* on the console the user should execute

the desired scan. See the comments in the header of the script for further details.

For use on a **Arduino** the ``JTAGenum.ino`` sketch is loaded. The Arduino pins 

being used for scanning should first be specified at the top of the sketch. This

is all that is required for basic JTAG scanning functionality. Once the 

correct JTAG pins on the target have been determined they can be specified in 

the script and along with the defining the proper IR_LENGTH the user can then

execute the search for hidden instructions or print the boundary scan register.

Before loading the sketch first define the pins[] and pinnames[] arrays. After

loadin the sketch open a serial console at baud of 115200 to access the 

user interface.  Sending a h to the console will print usage information that 

describes each function. Each function is enacted by sending the defined one 

character code:

**v > verbose**

Toggles verbose output. At times verbose might present too much

information or without it too little.

**l > loopback check**

Find loopback pairs that will generate false-positives for other

tests. After running you should remove any loopback pairs from your

pins[]/pinnames[]. Looback pairs are found by sending a predetermined

pattern[] to all possible pins while checking all pins for matching

output.  Because the JTAG clock (TCK) and state (TMS) pins are NOT

being stimulated the input/output pairs where the pattern is found

represent loopbacks. NOTE: you should probably run this once with

and without internal pull-up resistors set (r) to avoid problems

of cross-talk which is discussed in detail later.

**s > scan**

This routine is used to check all possible pins and find JTAG  clock,

state, input and output pins lines (TCK,TMS,TDI,TDO). This is done

by setting the JTAG state (TMS) into Shift_IR mode and then sending

pattern[] to TDI and checking for it on TDO while clocking TCK.

This check is run for every possible pin combination and it is

important that you remove loopback pins before running. While this

scan is meant to determine all of the JTAG pins required it is

possible that the  TMS pin found is incorrect.  This depends on if

the target uses the bypass register by default (described later).

If an IDCODE register is present then bypass mode is not the default

and you can assume that the pin this scan defines as TMS is correct.

Otherwise, only the TCK, TDI and TDO pins can be determined.  NOTE:

run with pull-ups on (r) as any cross-talk might result in

false-positives.

**y > brute force IR search**

This will set the instruction register (IR) to all possible values

and check the output. This can be used to find undocumented

instructions and examine their results via the data register (DR).

To run this scan you should have already determined the 4 JTAG pins

and define pins[] as such: [0]=TCK [1]=TMS [2]=TDO [3]=TDI.  NOTE:

run with pull-ups on (r) as any cross-talk might result in

false-positives.

**x > boundary scan**

This will return the state of all the pins on the target.  Actually

it is not just the pins but the contents of the scan/sample register.

This should be a rather large register and is defined in the code

by SCAN_LEN+100. You can check your targets documentation and specify

this or just leave it as a large number (currently 1800). To run

this scan you should have already determined the 4 JTAG pins and

define pins[] as such: [0]=TCK [1]=TMS [2]=TDO [3]=TDI.  NOTE: run

with pull-ups on (r) as any cross-talk might result in false-positives.

**i > idcode scan**

The JTAG standards specify that if an idcode register is present

it should be set as the default data register (DR) and attached to

output (TDO) by default. Meaning, regardless of the state of the

JTAG chip (set with TMS line) and regardless of input being sent

to the chip (TDI) by clocking the chip (TCK) it should return the

contents of the idcode to the output (TDO). Hence, this routine

iterates through all possible TCK,TDO pairs of pins and prints the

output when it changes (we assume an idcode will not be all 0s or

1s). You should examine the documentation of your target(s) to see

if the idcode matches. NOTE: run with pull-ups on (r) as any

cross-talk might result in false-positives.

**b > shift_bypass**

Broken atm (need to add TCK enumeration). The JTAG standards specify

that if and idcode register is NOT present on the chip then the

bypass register (length of 1) should be the default DR. Essentially

this means what is sent to the input (TDI) should come out on the

output (TDI) with a one clock delay (TCK). It is important that you

remove loopbacks before running this test otherwise the loopback

pins will look like valid JTAG lines. NOTE: run with pull-ups on

(r) as any cross-talk might result in false-positives.

**r > set pull-up resistors & cross-talk**

If like me the cables you use to connect between JTAGenum to your

targets are flimsy or uninsulated you might run into issues of

cross-talk whereby when one pin is transmitting a nearby pin picks

up the transmission even though they are not connected. To avoid

this you can turn on the internal pull-up resistors which will force

the pin to a default state. If for some reason you continue to have

sporadic issues run the following in sequence to check if the problem

is the cable, target or other:

1. Disconnect the cables between your target and JTAGenum. Disconnected them

   entirely from JTAGenum as well.

2. Run a loopback check (l) with pull-ups off. In this state the pins are in

   open mode and might fluctuate.  Youll notice that as you move the

   microcontroller around, turn lights on and off or move other devices close

   to or away from it that the results change.

3. Turn on pull-ups (r) and run the test again. The results should now be

   consistent. If they arent, then let me know.

4. Now attach your cables to JTAGenum but not the target. Run steps 2 and 3

   again. Step 2 will give you a feel for how much inconsistency the cable may

   add. If the loopback check results in actual pattern matches then your cable

   has cross-talk. Step 3 should still result in a consistent state of either

   all high (1s) or all low (0s) and if it doesnt then your cross-talk issues

   are such that all JTAGenum tests are going to be buggy at best. Feel free to

   give me an email and I will happily try to help solve the problem.

A bit about JTAG

================

Basic understanding of how JTAG works will be helpful when using

JTAGenum. There are 4 lines/pins: TDO=output, TDI=input, TCK=clock,

TMS=state machine control.  Say you want to read the ID of the chip.

First you would send the IDCODE instruction to the instruction

register (IR). The JTAG controller then places the actual id code

value of the chip in a data register which you could then read out.

You would think that it would be enough to have one input line going

to the IR and one output coming from the DR but JTAG also supports

writing to the DR. As apposed to adding another input line specific

to the DR instead JTAG works by moving the input and output lines

between IR and DR. The TMS line is used to switch TDI/TDO to IR

when you want to place an instruction and back to DR when you want

to read or write data. With all operations, be it state change (TMS)

reading (TDI) or writing (TDO), the clock line must be cycled once

(TCK) for every bit or change. This was a brutal and drastic

simplification but with that understood reading the Usage section

should be comprehensible.

For a more detailed discussion of JTAG see 

https://github.com/cyphunk/JTAGenum/wiki

TODO

====

1. upload pictures of the hardware setups

2. add ESP32 support

4. BusPirate bitbang support