nRF5340 - UART boot mode selection

RE: nRF5340 - UART boot mode selection

Gabriele — Tue, 07 Apr 2020 09:57:50 GMT

Thanks.

RE: nRF5340 - UART boot mode selection

haakonsh — Mon, 06 Apr 2020 07:41:39 GMT

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

RE: nRF5340 - UART boot mode selection

Gabriele — Fri, 03 Apr 2020 12:40:38 GMT

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

RE: nRF5340 - UART boot mode selection

haakonsh — Fri, 03 Apr 2020 10:18:27 GMT

[quote user="gabrielef@cosmed.it"]Does a Soft Reset pull low the reset pin ?[/quote]

No.

[quote user="gabrielef@cosmed.it"]Another question is how long it takes a system reboot ?[/quote]

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

RE: nRF5340 - UART boot mode selection

Gabriele — Fri, 03 Apr 2020 09:30:12 GMT

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

RE: nRF5340 - UART boot mode selection

haakonsh — Wed, 25 Mar 2020 13:44:36 GMT

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

RE: nRF5340 - UART boot mode selection

Gabriele — Wed, 25 Mar 2020 13:30:02 GMT

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 ?

RE: nRF5340 - UART boot mode selection

haakonsh — Wed, 25 Mar 2020 13:21:31 GMT

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

RE: nRF5340 - UART boot mode selection

Gabriele — Wed, 25 Mar 2020 12:43:13 GMT

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.

RE: nRF5340 - UART boot mode selection

haakonsh — Wed, 25 Mar 2020 12:07:07 GMT

Well, I'd still connect the ext MCU to nRESET, it's a good last resort if the nRF53 locks up for a currently unknown issue, but you do not need R1 or Q1. nRESET has an internal 13k pull-up, so if you configure AL27/P0.24 as high impedance the nRF device will not reset, then you configure it as output low when you need to reset the nRF device.

RE: nRF5340 - UART boot mode selection

Gabriele — Wed, 25 Mar 2020 10:38:07 GMT

Perfect,
that means I can throw away also this circuit.
Thanks

RE: nRF5340 - UART boot mode selection

haakonsh — Wed, 25 Mar 2020 10:23:11 GMT

[quote user="gabrielef@cosmed.it"]I guess P18 is the one I have to replicate on my board.
Is it correct ?[/quote]

Yes, you're correct.

[quote user="gabrielef@cosmed.it"]For the BOOT_SERIAL_DETECT_PIN mechanism to work, is a Soft Reset equivalent to a Pin Reset ?[/quote]

For DFU purposes yes, as the bootloader is the first piece of code executed after a reset. A soft reset resets the CPU only, a pin reset resets the rest of the MCU as well.

RE: nRF5340 - UART boot mode selection

Gabriele — Wed, 25 Mar 2020 09:36:33 GMT

For production programming the SWD method would be fine.
On the PDK I see two different SWD interfaces

P18 (Debug In)
P19 (Debug Out)

I guess P18 is the one I have to replicate on my board.
Is it correct ?

A second question is about nRF5340 reset in relation to DFU.
I want to keep the BOOT_SERIAL_DETECT_PIN as a backup DFU mechanism.
For the BOOT_SERIAL_DETECT_PIN mechanism to work, is a Soft Reset equivalent to a Pin Reset ?

RE: nRF5340 - UART boot mode selection

haakonsh — Tue, 24 Mar 2020 10:26:25 GMT

Are you asking about production programming? If so you need VDD, GND, SWDIO, and SWDCLK exposed to an SWD programmer interface.

You need to program at least the bootloader and a DFU with the UART interface during production.

An alternative is to create an SWD interface in the other MCU and use that to program the nRF device, this can serve as the future DFU process as well. Though I would not recommend it unless you've got large volume production as it is a fair bit of development involved.

RE: nRF5340 - UART boot mode selection

Gabriele — Tue, 24 Mar 2020 10:11:26 GMT

Sorry, one last question. So far we dealt with DFU handled by a custom FW.
What about the very first DFU ?
How do I do it ?

RE: nRF5340 - UART boot mode selection

Gabriele — Mon, 23 Mar 2020 15:04:33 GMT

Good idea! I'll get rid of the circuit.

RE: nRF5340 - UART boot mode selection

haakonsh — Mon, 23 Mar 2020 15:00:43 GMT

If the ext MCU will send a UART command to the application then you can just store that state in persistent storage and issue a system reset, then check for that state in the bootloader. In that case, you won't need the BOOT_SERIAL_DETECT_PIN signal at all.

RE: nRF5340 - UART boot mode selection

Gabriele — Mon, 23 Mar 2020 14:11:07 GMT

Great.

In my application the user cannot put her hands on the board, to press buttons etc. Thus DFU must be entirely managed by SW.
This is the idea (look at the circuit)

a) the user sends a command like "please, DFU on next reboot"
b) the nRF5340 sets DFUEN high long enough to charge the capacitor, then resets the board
c) on reboot DFUBOOTn is found low, and the DFU process starts
d) during the DFU process, the capacitor discharges through the large resistor

RE: nRF5340 - UART boot mode selection

haakonsh — Mon, 23 Mar 2020 13:18:52 GMT

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.

RE: nRF5340 - UART boot mode selection

Gabriele — Fri, 20 Mar 2020 13:21:27 GMT

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

RE: nRF5340 - UART boot mode selection

haakonsh — Fri, 20 Mar 2020 12:37:45 GMT

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.

RE: nRF5340 - UART boot mode selection

Gabriele — Fri, 20 Mar 2020 12:28:55 GMT

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 ?

RE: nRF5340 - UART boot mode selection

haakonsh — Wed, 18 Mar 2020 10:51:41 GMT

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