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

[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]

Hi haakonsh.

I've made substantial progress on the hardware design. There is space for a little improvement.
We agreed that for bootloader restart the Soft Reset is sufficient.
Now I've realized I need to reset some external circuitry when rebooting programmatically.
Does a Soft Reset pull low the reset pin ?

Another question is how long it takes a system reboot ? I mean the time elapsed form a Soft Reset to a system ready condition under Zephyr.

Thanks for your valuable support
Gabriele

[haakonsh]

Gabriele said:

Does a Soft Reset pull low the reset pin ?

 No. 

Gabriele said:

Another question is how long it takes a system reboot ?

It depends on your specific build of zephyr. I can try to find some numbers that might be relevant.

[Gabriele]

Yes, please. Even a rough value would be fine to know

[haakonsh]

It's anything from a few ms to 500ms, depending on a vast number of variables. 

[Gabriele]

Thanks.