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]

That's clear, for bootloader restart the Soft Reset is sufficient.
But if the nRF53 locks up for an unknown issue, it will not respond on the UART and then the user will be adviced to power cycle the system.
This is because the system comprises only the nRF53. There is no external MCU.

[haakonsh]

Aah, So I guess you only connect to another device over uart when you need the DFU. 

[Gabriele]

It is linked to a PC just through the serial port, not only for DFU but also for normal operation. DFU is only one command in the list the PC could send to the nRF.
Make sense ?

[haakonsh]

Yeah, that makes sense.
A power-cycle is just as effective as a pin reset, so you can ditch that circuit as well. 

[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.