Mode 3 provides a tool to scan for JTAG and SWD pinouts on a board.
The implementation is lifted from JTAGenum and SWDscan, for which we are very grateful.
Pinout
Any pin marked as "test pin" below can be probed. Actual pins probed depends on the command used to scan, see dpctl.
Raspberry Pico
On the Raspberry Pico, 20 pins can be used:
| Pin number |
Usage |
Usage |
Pin number |
| GP0 |
stdio UART TX |
|
VBUS |
| GP1 |
stdio UART RX |
|
VSYS |
| GND |
<ground> |
<ground> |
GND |
| GP2 |
Test pin |
|
3V3 EN |
| GP3 |
Test pin |
|
3V3 OUT |
| GP4 |
Test pin |
|
ADC VREF |
| GP5 |
Test pin |
|
GP28 / ADC2 |
| GND |
<ground> |
<ground> |
GND / AGND |
| GP6 |
Test pin |
|
GP27 / ADC1 |
| GP7 |
Test pin |
|
GP26 / ADC0 |
| GP8 |
Test pin |
|
RUN |
| GP9 |
Test pin |
Test pin |
GP22 |
| GND |
<ground> |
<ground> |
GND |
| GP10 |
Test pin |
Test pin |
GP21 |
| GP11 |
Test pin |
Test pin |
GP20 |
| GP12 |
Test pin |
Test pin |
GP19 |
| GP13 |
Test pin |
Test pin |
GP18 |
| GND |
<ground> |
<ground> |
GND |
| GP14 |
Test pin |
Test pin |
GP17 |
| GP15 |
Test pin |
Test pin |
GP16 |
| <end> |
<bottom> |
<bottom> |
<end> |
Usage
This mode is controlled entirely through dpctl.
Time spent scanning is proportional to n_pins_probed nCr n_pins_in_itf, i.e. n_pins_probed!/(n_pins_probed-n_pins_in_itf)!. For JTAG, n_pins_in_itf is equal to 5, for SWD, it is 2. n_pins_probed depends on the start and end arguments passed to dmctl.