NRF52840: VDD ramp-up to main() time.

[Hrishi]

Hi,

How much is the expected time period from the time VDD goes above 1.75V to main()? I am using a custom bootloader and am seeing a ~4.5s (yes seconds!) delay in getting to bootloader main(). When the debugger is connected this time is in the 100s of ms, which is what I would expect without the bootloader on first power up (1.8V VDD rail starting up). Here's a scope shot of my 1.8V rail (CH2) starting up and the IO (CH1) toggling (one of the first things done inside main()). Any help is greatly appreciated.

Thanks.

Hrishi

[Kenneth]

Hrishi said:

Could there be something in the boot-up process that may cause a long delay?

The below text you write that it takes ~4.5 to enter main(), so it must be electrical. I do not see how software can have anything to do with this no, since it doesn't start running any code here before you enable LED. My best suggestion is to check if VDD = 2V solve the issue (even if that will mean you have to modify the the hardware).

seeing a ~4.5s (yes seconds!) delay in getting to bootloader main()

[Hrishi]

I guess you are saying that from the time nrf52840 VDD gets above 1.75V (according to the datasheet) to the time the PC enters main.c of the bootloader I should see a time delay muc much less than 4s, correct?

Hmm this is strange. 

[Hrishi]

The BMD-340 module is getting that 1.8V VDD bus I shared in the scope shot earlier.

[Kenneth]

Hi, Is there any way you can send hardware here we may use to recreate it?

Is there any way you may try with 2V?

How have you electrically connected the BMD-340? Do you have a table that show pin connections for the module?

Were you able to try: ...open the module to find the exact chip markings? 

Hrishi said:

I guess you are saying that from the time nrf52840 VDD gets above 1.75V (according to the datasheet) to the time the PC enters main.c of the bootloader I should see a time delay muc much less than 4s, correct?

That is correct! Starting up an external 32kHz may be in the hundreds of ms, but in your case I assume you are toggling that LED in the beginning of main() so that should not apply.

[Hrishi]

Hi Kenneth,

Here's a part of the relevant schematic, which shows how the BMD-340 power pins are connected:

Here's the waveform seen at pin 39 (MCU_RSTn) along with the VDD_1V8 bus

Also for completeness my previous scope capture with the VDD_1V8 rail and the GPIO that gets toggled at the start of the bootloader main.c.

Thanks.

Hrishi