Weird Issue observed with Nrf52832

RE: Weird Issue observed with Nrf52832

hmolesworth — Fri, 25 Dec 2020 00:02:03 GMT

Something else to think about, pardon me if you already know this. Once the reset pin is actually working as a reset pin (more on this in a while) erasing all flash does not stop it being a reset pin until after a full reset takes place, either via the reset pin or power cycle or other. The Flash registers which control the pin are only read following a reset, so until a reset happens the fact that the registers are erased is not recognised.

Once the reset pin is no longer a reset pin (erase all, hard reset or power cycle) and you set it to be a reset pin (write to the Flash registers) it does not become a reset pin until after a hard reset which is of course not possible by using the reset pin (in this case). If using Nordic examples, setting the pin as a reset pin automatically generates the required reset in software, but if setting by other means then the pin won't reset until after some other reset.

That's basically what your option 1 is doing, but the reset pin might not be a reset pin depending on what you did earlier and so may not reset, for example if you do 2 recover reset cycles. So .. --pinreset might not, and what is --reset?

RE: Weird Issue observed with Nrf52832

Nguyen Hoan Hoang — Thu, 24 Dec 2020 23:18:17 GMT

Option 1. A hard reset is required after recover.

option 2. will not work reliably

RE: Weird Issue observed with Nrf52832

VishnuGS — Thu, 24 Dec 2020 22:43:41 GMT

Hello hmolesworth,

Thanks for your reply.

I will consult my HW engineers to see a quick way of discharging my bulk capacitors.

About, J-link circuitry disconnection, I have tried that.

In my Second procedure, while waiting for 15 minutes I disconnected my custom board with all other external circuitry.

Thanks.

RE: Weird Issue observed with Nrf52832

VishnuGS — Thu, 24 Dec 2020 22:39:52 GMT

Hello Nguyen Hoan Hoang,

Thanks for your reply.

Did you mean,

Option 1:

Recover(from preloaded APP FW) -> --pinreset -> Flash HQ Test FW -> --reset -->Test

Option 2:

Recover(from preloaded APP FW) -> Flash HQ Test FW -> --pinreset --> Test

And you do you mean by,

Since I am not doing hard reset, Even though I recovered from Main App FW, Normal Operation can not be guaranteed with my HQ Test FW?

My Second procedure as mentioned in the ticket description where I try to power cycle the board helped to get it work?

Thanks again for your response.

RE: Weird Issue observed with Nrf52832

hmolesworth — Thu, 24 Dec 2020 22:09:20 GMT

To add to Nguyen's reply there are some power issues to consider. Once the power supply is removed or switched off the bulk capacitance you mention starts to discharge. Once that capacitor voltage falls below some magic figure the nRF52832 will no longer be executing code and all port pins are in reset condition and so do not dissipate power; this means current consumption is extremely low, just a few 10s of nA. Note the voltage on the bulk capacitance has not discharged completely yet, and the voltage is high enough to prevent the nRF52832 reset circuitry from properly operating, so it is possible to restore power, fiddle with recover tools but yet be unable to actually get a working product.

The Work-around

The 15-minute delay allows the bulk capacitance to discharge below the magical reset voltage minimum-level-to-work-at-all, so now fiddling with tools and reprogramming works fine. Note that the discharge to near zero of the bulk capacitor is likely not through the nRF52832 draining the capacitor, but by other circuit elements - including capacitor leakage - which are likely to have higher leakage than the nRF52832 itself at low voltages of less than 1 volt.

The Test

Turn off the power and immediately short all the bulk capacitors with a Gnd wire thus discharging them, Immediately switch back on and verify the recover-program procedure you are hoping for without using a 15-minute delay.

The Fix

Add a crowbar, either on-board or off-board. This is a means of short-circuiting the capacitor to discharge quickly. Some regulators have this built-in, but most don't and an external FET or other dummy load is required. It doesn't need to be a short-circuit, just a low enough resistance to discharge all capacitors in the required time. Some capacitors are before and some after regulators, so some circuit knowledge is required.

Stuff to Watch For

Any external device or circuit - say an FTDI serial link or a J-Link debugger tool - will add to the problem as they back-drive any parts of the circuit they are connected to making the problem worse and discharge slower, and can even prevent any reset and recover at all. If not already disconnecting the programmer when power-cycling then doing so may even be a simple fix.

Nordic engineers have to look after the reindeer and gifts this time of year, but when back they might have some voltage figures to quote; I don't think the data sheet can be relied on here as the figures we need are not really specified, but the required discharge voltage is pretty low maybe 400mV or less.

RE: Weird Issue observed with Nrf52832

Nguyen Hoan Hoang — Thu, 24 Dec 2020 21:08:24 GMT

Recover from protection or set protection or any change for the reset pin or NFC pins requires a full reset, either by power cycle or hard reset