GPIO pin settings when moving from Bootloader to Application mode

[beemavishnu]

Hi,

 

I am using nRF52840 S140 with ble_app_blinky application. I have a basic query of GPIO configuration when moving from Bootloader to Application.

 

We are using Secure Serial Bootloader. Via DFU we will load our BLE blinky application package. In Secure Serial bootloader code, P0.25 is configured as input and Pull-UP. So pin will be always high. Where as in blinky application we are not configuring any GPIO pins other than button and led.

 

After every reset of nRF chip, control will go to Bootloader mode. If P0.25 is low then only bootloader will enter into DFU mode. If pin is high control will immediately go to ble_blink application.

 

My queries are:

1) Whatever pin configurations done in bootloader, whether the same settings will retain even when control goes to ble_blink.

2) If yes, if P0.25 is configured as PullUP in bootloader, to my understanding I can configure P0.25 to PullDown in ble_blink application.

 

Thanks & Regards

Vishnu Beema

[Edvin]

Hello Vishnu,

1) When the device is reset, all the pins are set as disconnected inputs (the state that doesn't draw any power/current). I am not sure exactly what happens when you go from the bootloader to the app. I would imagine that they would be reset again, but perhaps they are manually reset (the UART and button pin are disabled).

2) Either way, you can change this in the application, yes.

Based on how you ask this question, I suspect that you want to change the configuration after entering the application, is that correct? Have you noticed the NRF_BL_DFU_ENTER_METHOD_BUTTON in the bootloader project? Look how this is used in nrf_bootloader_init() in nrf_bootloader.c. If you want to decide whether or not to enter DFU mode based on a pin input, I guess you can use that. After you start your application, you can do whatever you like to the GPIOs.

Best regards,
Edvin

[beemavishnu]

Hi,

 

Yes NRF_BL_DFU_ENTER_METHOD_BUTTON is enabled. I am trying to understand your statement "I would imagine that they would be reset again, but perhaps they are manually reset ".

 

Irrespective of P0.25, assume I configure few pins in bootloader as PULLUP. Now if I reset chip, control will go to bootloader configure gpio pins as PULLUP and since P0.25 is not Low control will be given to Application mode. In Application mode if I don't configure gpio pins will these pins retain PULLUP state as the same configured in bootloader or will reset to default state NOPULL.

 

Can you please crosscheck with your R&D team. Unfortunately I am not in office. Otherwise I would have tested using CRO by configuring few pins.

 

Thanks & Regards

Vishnu Beema

[Edvin]

beemavishnu said:

I am trying to understand your statement "I would imagine that they would be reset again, but perhaps they are manually reset ".

 What I meant was that in an unmodified bootloader + application, the configuration of pins from the bootloader doesn't follow into the application. E.g. if the application uses UART, the UART pins will either be reset in the transition from bootloader->application or the pins will be reset due to some UART deinit function.

However, I see that this is not the case for the button used in NRF_BL_DFU_ENTER_METHOD_BUTTON. By default, this is set to button 4 (pin P0.25). Remember that you can read out the GPIO configuration. The registers are listed on InfoCenter:

https://infocenter.nordicsemi.com/topic/ps_nrf52840/gpio.html?cp=4_0_0_5_8_1_9#register.PIN_CNF-0-31

So for pin 25 that would be address 0x50000764. If you read this address using nrfjprog --memrd 0x50000764 after programming the bootloader, you will see that it has the value 0x0003000C. If you change the bootloader define in sdk_config.h:

#define NRF_BL_DFU_ENTER_METHOD_BUTTON_PIN 25
to
#define NRF_BL_DFU_ENTER_METHOD_BUTTON_PIN 26

You will see that address 0x50000768 (pin 26) reads 0x0003000C.

If you also perform a DFU, so that your chip contains a bootloader and an application, and you start the application, you can see that pin 26 is still set to 0x0003000C, meaning it has a pullup, and is a connected input with sense for low level, even if your application didn't initialize anything on pin P0.26.

The reason I tested with button pin 26 is that most examples initialize the buttons with the same settings, and pin P0.25 is Button4 on the DK.

This means that if you want different behavior on the pins in your bootloader and application, you must set this in the application.

Best regards,

Edvin

[beemavishnu]

Thank you for your inputs and confirmation.