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JTAGscan

JTAGscan allows you to find JTAG ports without buying specialized hardware like the JTAGulator. All you need is a Arduino compatible board and optionally a logic level shifter.

How does it work?

JTAGscan iterates through configured set of pins to find the JTAG TMS, TCK, TDO and TDI lines using two approaches:

• by reading ID CODE to find TMS, TCK and TDO, TDI is found by shifting bits in BYPASS mode
• by shifting bits in BYPASS mode to find TMS, TCK, TDO and TDI The first approach is quicker and thus preferred.

Unfortunately not all chips support ID CODE retrieval so BYPASS mode scan will be needed for them.

How to use it?

• hook up your Arduino to the target
• use a logic level shifer between Arduino and target if required
• adjust PIN_MASK for your setup (can be done later using m)
• select proper build target
• build the project and upload it to your board
• establish serial connection with baud rate of 115200
• ammend debug options if required
• use option h for help
• use option a to automatically enumerate pins using available methods

How to set the pin_mask?

Pins are enabled by setting corresponding bits of PIN_MASK, i.e. pins 2-8 are enabled for PIN_MASK of 0b111111100 or 0x1fc.

Besides PIN_MASK predefined at build time you can also set the pin mask at runtime using the m command. Entering 508 or 0x1fc will result in pin_mask set to 0b111111100 so you can update the configuration without the need to rebuild the project.

How does it look like?

• help

> h
+-------------------------------+
|  JTAGscan Jtag Pinout Finder  |
+-------------------------------+
 a - Automatically find all pins
 i - IDCODE search for pins
 b - BYPASS search for pins
 t - TDI-only BYPASS search
 m - set pin mask, current: 0xFC
 d - set debug level: 1
 c - half cycle us, current: 32
 h - print this help
+-------------------------------+

• automatic enumeration on a Kinetis based board

> a
     Automatically searching
+-- Starting with IDCODE scan --+
| TCK | TMS | TDO |      IDCODE |
+-------------------------------+
|   2 |   3 |   0 |    cba00477 |
+----------- SUCCESS -----------+
    TCK, TMS, and TDO found.

+-- BYPASS searching, just TDI -+
| TCK | TMS | TDO | TDI | Width |
+-------------------------------+
|   2 |   3 |   0 |   1 |    31 |
+----------- SUCCESS -----------+

• toggle debug level to 1, then ID CODE enumeration of TCK, TMS and TDO lines

> d
Debug level set to 1
> i
+------ IDCODE searching -------+
| TCK | TMS | TDO |      IDCODE |
+-------------------------------+
|   0 |   1 |   2 |           0 |
|   0 |   1 |   3 |           0 |
|   0 |   1 |   4 |           0 |
|   0 |   1 |   5 |           0 |
|   0 |   2 |   1 |           0 |
|   0 |   2 |   3 |           0 |
|   0 |   2 |   4 |           0 |
|   0 |   2 |   5 |           0 |
...
|   2 |   0 |   1 |           0 |
|   2 |   0 |   3 |           0 |
|   2 |   0 |   4 |           0 |
|   2 |   0 |   5 |           0 |
|   2 |   1 |   0 |           0 |
|   2 |   1 |   3 |           0 |
|   2 |   1 |   4 |           0 |
|   2 |   1 |   5 |           0 |
|   2 |   3 |   0 |    4ba00477 |
+----------- SUCCESS -----------+
| TCK | TMS | TDO |      IDCODE |
+------ IDCODE complete --------+

• enumeration of TDI following a ID CODE scan

> t
+-- BYPASS searching, just TDI -+
| TCK | TMS | TDO | TDI | Width |
+-------------------------------+
|   2 |   3 |   0 |   1 |    31 |
+----------- SUCCESS -----------+

• full identification of lines using BYPASS mode

> b
+------ BYPASS searching -------+
| TCK | TMS | TDO | TDI | Width |
+-------------------------------+
|   0 |   1 |   2 |   3 |     0 |
|   0 |   1 |   2 |   4 |     0 |
|   0 |   1 |   2 |   5 |     0 |
|   0 |   1 |   3 |   2 |     0 |
|   0 |   1 |   3 |   4 |     0 |
|   0 |   1 |   3 |   5 |     0 |
|   0 |   1 |   4 |   2 |     0 |
|   0 |   1 |   4 |   3 |     0 |
|   0 |   1 |   4 |   5 |     0 |
...
|   2 |   1 |   4 |   3 |     0 |
|   2 |   1 |   4 |   5 |     0 |
|   2 |   1 |   5 |   0 |     0 |
|   2 |   1 |   5 |   3 |     0 |
|   2 |   1 |   5 |   4 |     0 |
|   2 |   3 |   0 |   1 |    31 |
+----------- SUCCESS -----------+
| TCK | TMS | TDO | TDI | Width |
+------ BYPASS complete --------+

No Platformio?

No problem, just copy the contents of src/main.cpp to a new Arduino project, remove the Arduino.h import from the first line and you're ready to go.

Using ARM?

Check SWDscan to identify the Serial Wire Debug pins.