JTAG Pins

JTAG pins can be switched in 2 ways:

• Burning JTAG efuse bits (jtag_cfg key)
• Runtime remapping in user program

Here is an example switching default mapping to pins 16 17 18 19:

1. Make Efuse image and its mask, provided for convenience in there They are composed of 2 elements, the efuse bin, which sets the value (0x96 at 0x5D here), and efuse_mask bin, which sets the modification mask (we only want to modify a single bit, so we put 0x4 at 0x5D).
2. Copy the 2 files to chips/bl616/efuse_bootheader/, overwrite if other files of same name are present.
3. Open Devcube, enable advanced pages, and go to the ‘Efuse’ tab.
4. Setup your settings on the right side and your device, do not click any buttons, especially program or create. Set AES Mode to None and verify no locks or keys are set.
5. Press the Program button.
6. Verify by resetting the device into flash mode, pressing the Read button, and opening the file efuse.bin next to devcube executable that 0x5D is now 0x96 instead of 0x92

BL616CL may come with the efuses enabling JTAG unburnt.

To enable JTAG, or switch to other pinouts (1: 20-23, 2: 12-13 18-19, 3: 8-11), the bits 6 to 8 at efuse address 0x70 may be set. Example using BLFlashCommand.

1. Read efuses for your chip: ./BLFlashCommand-ubuntu --chip bl616cl --read --efuse --start 0x0 --len 0x80 --file the_efuses.bin
2. Modify the binary file, for example with okteta, such that the appropriate bits are set. Remember the first byte at the address is 7-0 and the last one (0x73) is 31-24. For me, the byte at 0x70 was 0x02, I changed it to 0x62 (bit 5 enables USB flashing) such that the sequence in okteta was 62 E0 55 00 at 0x70.
3. Burn the efuses: ./BLFlashCommand-ubuntu --chip bl616cl --efusefile the_efuses.bin
4. Check the result is as expected by re-reading the fuses.

Runtime remapping is done by first disabling the JTAG function of the default pins, and then configuring the new chosen pins to provide the JTAG functionality.

Bare Example for Thirdreality Temperature and Humidity Sensor Lite