nRF5340 - UART boot mode selection

[Gabriele]

Hello,

I want to program nRF5340 via UART.

What is the hardware related event that puts the application processor in program mode over the UART ?

All ARM microprocessors I've worked with have special pins with "boot-mode" function.
When the device reset is deasserted, the boot mode selection is determined by the logic values of these pins.
I suppose nRF5340 does the same. Or not?

I'm in the hardware design process, and need to fix this.

Regards,
Gabriele

[haakonsh]

Any available GPIO can be used. 

See https://github.com/NordicPlayground/fw-nrfconnect-mcuboot/blob/master/boot/zephyr/Kconfig#L296. 
and https://github.com/NordicPlayground/fw-nrfconnect-mcuboot/blob/master/boot/zephyr/main.c#L223

[Gabriele]

Thanks haakonsh,

Kconfig tells that BOOT_SERIAL_DETECT_PIN is "11" for BOARD_NRF52840_PCA10056.
In the HW schematics of PCA10056 the RESET pin is P0.18.
How does P0.18 relates to 11 ?

[haakonsh]

You're mixing two concepts here. The reset pin called nRESET is used to reset the MCU, in case of the nRF52840 this pin can be configured as a GPIO instead.

The BOOT_SERIAL_DETECT_PIN is used to signal the bootloader that you wish to start the DFU procedure.

[Gabriele]

If I understand well,
P0.18 is the reset pin
P0.11 is the in to get monitored to start DFU
Is it correct ?

[haakonsh]

Yes, the bootloader checks the BOOT_SERIAL_DETECT_PIN during boot and starts the DFU process. The reset pin is used to start the bootloader.