SWCU192 November 2021 CC1312R7 , CC1352P7 , CC2652P7 , CC2652R7
To enter the ROM bootloader even when a valid image is in the flash, a bootloader backdoor is implemented. The CCFG parameter BL_ENABLE can enable this backdoor. The backdoor functionality uses a configurable I/O pin (CCFG parameter BL_PIN_NO) and a configurable I/O pin level (CCFG parameter BL_LEVEL).
If backdoor functionality is enabled, externally applying a configurable signal level on a configurable I/O pin can force a ROM bootloader entry upon reset. If the backdoor is enabled and a valid flash image is present, start-up code checks the level of the I/O pin. If the configured I/O-pin level matches the configured signal level, the ROM bootloader does not transfer control to the flash image.
If the backdoor pin configuration matches one of the UART0 or SSI0 pins, the external user must deassert the backdoor signal before transmitting on the UART0 or SSI0 interface.
In TI distributed software, the CCFG parameters called BL_ENABLE, BL_PIN_NO and BL_LEVEL are configured by the values of the following defines in the ccfg.c file:
Section 12.2.1 shows the BL_BACKDOOR_CONFIG parameter layout in CCFG.
When using the bootloader backdoor functionality, the pin configured as backdoor (BL_PIN_NO) will be configured to enable a pull level opposite of the configured I/O pin level while checking the backdoor level.