DFU over USB - nRF52840 running Zephyr

RE: DFU over USB - nRF52840 running Zephyr

bojan — Thu, 06 May 2021 08:50:11 GMT

Hey, Einar.

I already shared how I write to GPREGRET/GPREGRET2 registers in one of my above messages. Now, when I compare that with the code you shared, I am realizing I did it wrong. I did not use NRF_POWER as a function argument, that was my mistake. 🤦🏻

I confirm that both GPREGRET/GPREGRET2 registers are keeping the value written to them before a soft restart with NVIC_SystemReset() function. Consequently, I was able to enter DFU mode without pressing any button (butonless DFU)! Thanks for bearing with me!

One more observation I wanted to share with you... because of the following piece of code inside MCUBoot bootloader (bootloader\mcuboot\boot\zephyr\main.c):

#ifdef CONFIG_MCUBOOT_SERIAL

    struct device const *detect_port;
    uint32_t detect_value = !CONFIG_BOOT_SERIAL_DETECT_PIN_VAL;

    detect_port = device_get_binding(CONFIG_BOOT_SERIAL_DETECT_PORT);
    __ASSERT(detect_port, "Error: Bad port for boot serial detection.\n");

    /* The default presence value is 0 which would normally be
     * active-low, but historically the raw value was checked so we'll
     * use the raw interface.
     */
    rc = gpio_pin_configure(detect_port, CONFIG_BOOT_SERIAL_DETECT_PIN,
#ifdef GPIO_INPUT
                            GPIO_INPUT | GPIO_PULL_UP
#else
                            GPIO_DIR_IN | GPIO_PUD_PULL_UP
#endif
           );
    __ASSERT(rc == 0, "Error of boot detect pin initialization.\n");

#ifdef GPIO_INPUT
    rc = gpio_pin_get_raw(detect_port, CONFIG_BOOT_SERIAL_DETECT_PIN);
    detect_value = rc;
#else
    rc = gpio_pin_read(detect_port, CONFIG_BOOT_SERIAL_DETECT_PIN,
                       &detect_value);
#endif
    __ASSERT(rc >= 0, "Error of the reading the detect pin.\n");
    if (detect_value == CONFIG_BOOT_SERIAL_DETECT_PIN_VAL &&
        !boot_skip_serial_recovery()) {
        BOOT_LOG_INF("Enter the serial recovery mode");
        rc = boot_console_init();
        __ASSERT(rc == 0, "Error initializing boot console.\n");
        boot_serial_start(&boot_funcs);
        __ASSERT(0, "Bootloader serial process was terminated unexpectedly.\n");
    }
#endif

CPU were entering DFU mode every time the board is power-cycled. Not only when Button 1 is held down while Reset button is pressed but every time the board is power-cycled. I disabled that piece of code and I am now entering DFU mode only through the GPREGRET2 register.

As a cherry on the top, it remains to replace the .pem key that comes with the MCUBoot bootloader with our own public/private keypair. I will feel free to create a new ticket if I face any difficulty there.

One more time, thanks for your great support!

Cheers, 🍻

Bojan.

RE: DFU over USB - nRF52840 running Zephyr

Einar Thorsrud — Wed, 05 May 2021 10:42:33 GMT

Hi,

That is odd. I have not found any code in NCS that write to GPREGRET2. Also, I did a very quick test using the basic blinky sample from Zephyr in NCS 1.5.1 where I just added CONFIG_BOOTLOADER_MCUBOOT=y in prj.conf and read and updated GPREGRET2 before doing a soft reset repeatedly, and that works as expected as you can see here:

Code:

devzone.nordicsemi.com/.../4454.main.c

Log:

*** Booting Zephyr OS build v2.4.99-ncs2  ***
I: Starting bootloader
I: Primary image: magic=unset, swap_type=0x1, copy_done=0x3, image_ok=0x3
I: Secondary image: magic=unset, swap_type=0x1, copy_done=0x3, image_ok=0x3
I: Boot source: none
I: Swap type: none
I: Bootloader chainload address offset: 0xc000
*** Booting Zephyr OS build v2.4.99-ncs2  ***
Started...
GPREGRET2 value: 0x00
*** Booting Zephyr OS build v2.4.99-ncs2  ***
I: Starting bootloader
I: Primary image: magic=unset, swap_type=0x1, copy_done=0x3, image_ok=0x3
I: Secondary image: magic=unset, swap_type=0x1, copy_done=0x3, image_ok=0x3
I: Boot source: none
I: Swap type: none
I: Bootloader chainload address offset: 0xc000
*** Booting Zephyr OS build v2.4.99-ncs2  ***
Started...
GPREGRET2 value: 0x01
*** Booting Zephyr OS build v2.4.99-ncs2  ***
I: Starting bootloader
I: Primary image: magic=unset, swap_type=0x1, copy_done=0x3, image_ok=0x3
I: Secondary image: magic=unset, swap_type=0x1, copy_done=0x3, image_ok=0x3
I: Boot source: none
I: Swap type: none
I: Bootloader chainload address offset: 0xc000
*** Booting Zephyr OS build v2.4.99-ncs2  ***
Started...
GPREGRET2 value: 0x02

Can you share how you read and write to GPREGRET2 in your app and in MCUBoot?

RE: DFU over USB - nRF52840 running Zephyr

bojan — Wed, 05 May 2021 07:54:19 GMT

I tried the same thing with the latest NCS v1.5.1 as well. Again, GPREGRET/GPREGRET2 registers have some constant value after soft reset no matter what I write into them before the soft reset. In the case of NCS v1.5.1 the value of those registers differ compared to the v1.4.2:

v1.4.2

Button has changed. State: 1
Button 1 pressed
Setting GPREGRET/GPREGRET2 registers...
Before soft reset. GPREGRET: 86
Before soft reset. GPREGRET2: 172
*** Booting Zephyr OS build v2.4.0-ncs2  ***
[00:00:00.254,730] <inf> mcuboot: Starting bootloader. Test!
[00:00:00.254,760] <inf> mcuboot: Checking GPREGRET/GPREGRET2 registers...
[00:00:00.254,760] <inf> mcuboot: System booting. GPREGRET: 195
[00:00:00.254,760] <inf> mcuboot: System booting. GPREGRET2: 246
[00:00:00.255,249] <inf> mcuboot: Primary image: magic=unset, swap_type=0x1, copy_done=0x3, image_ok=0x3
[00:00:00.255,249] <inf> mcuboot: Boot source: none
[00:00:00.255,371] <inf> mcuboot: Swap type: none
*** Booting Zephyr OS build v2.4.0-ncs2  ***

v1.5.1

Button has changed. State: 1
Button 1 pressed
Setting GPREGRET/GPREGRET2 registers...
Before soft reset. GPREGRET: 86
Before soft reset. GPREGRET2: 172
*** Booting Zephyr OS build v2.4.99-ncs2  ***
I: Starting bootloader
I: Checking GPREGRET/GPREGRET2 registers...
I: System booting. GPREGRET: 88
I: System booting. GPREGRET2: 191
I: Primary image: magic=unset, swap_type=0x1, copy_done=0x3, image_ok=0x3
I: Secondary image: magic=unset, swap_type=0x1, copy_done=0x3, image_ok=0x3
I: Boot source: none
I: Swap type: none
I: Bootloader chainload address offset: 0x10000
*** Booting Zephyr OS build v2.4.99-ncs2  ***

RE: DFU over USB - nRF52840 running Zephyr

bojan — Wed, 05 May 2021 06:59:40 GMT

Hello, Einar.

I tried the same thing with GPREGRET2 register but the same thing happens. No matter what I write into GPREGRET/GPREGRET2 registers, I always read 0xC3 and 0xF6, respectively, after soft resetting the CPU with NVIC_SystemReset() function.

RE: DFU over USB - nRF52840 running Zephyr

Einar Thorsrud — Tue, 04 May 2021 12:56:46 GMT

Hi Bojan,

The retention registers are retained during a soft reset (NVIC_SystemReset()) but not during a pin reset. I did not think about that. GPREGRET is allready in use by sys_arch_reboot() implementatino for nRF52 in zephyr\soc\arm\nordic_nrf\nrf52\soc.c, which is called by sys_reboot(). But GPREGRET2 seems to be unused, so if you use that instead I think you should be good.

The retention register is not cleared automatically, so you you want to clear it once you have read it in MCUboot and decided to enter DFU mode so that it does not repeat again on next reset and so on.

Einar

RE: DFU over USB - nRF52840 running Zephyr

bojan — Tue, 04 May 2021 11:41:08 GMT

Hello, Einar.

Thanks for your explanations!

I can report that resetting nRF via mcumgr using:

mcumgr --conntype=serial --connstring=<USB Serial Device> reset

after binary file is transferred over USB works fine!

Concerning the first question (entering DFU by GPREGRET), I tried what you suggested. Inside the application code, I tried to write the 0xB1 value into GPREGRET register and restart the board after that with the following piece of code:

static void reboot_into_bootloader(void) {  
  #define BOOTLOADER_DFU_GPREGRET_MASK            (0xB0)      
  #define BOOTLOADER_DFU_START_BIT_MASK           (0x01)  
  #define BOOTLOADER_DFU_START    (BOOTLOADER_DFU_GPREGRET_MASK | BOOTLOADER_DFU_START_BIT_MASK)
  NRF_POWER_Type gp_reg_ret;
  nrf_power_gpregret_set((NRF_POWER_Type *)&gp_reg_ret, BOOTLOADER_DFU_START);
  k_msleep(1500);
  uint8_t gp_reg;
  gp_reg = nrf_power_gpregret_get(&gp_reg_ret);
  printk("System resetting. GPREGRET: %d\n", gp_reg_ret.GPREGRET);
  printk("System resetting. GPREGRET: %d\n", gp_reg);
  NVIC_SystemReset();
}

On the other side, inside main.c file located at bootloader\mcuboot\boot\zephyr\main.c, I tried to read the content of GPREGRET register during the boot process with the following piece of code:

BOOT_LOG_INF("Checking GPREGRET register...");
NRF_POWER_Type gp_reg_ret;
uint8_t gp_reg;
gp_reg = nrf_power_gpregret_get(&gp_reg_ret);
BOOT_LOG_INF("System booting. GPREGRET: %d\n", (gp_reg_ret.GPREGRET & 0xFF));
BOOT_LOG_INF("System booting. GPREGRET: %d\n", gp_reg);

The content of GPREGRET register after restart is equal to 0xC3!

Do you have any idea why those two values differ? According to some threads (link), GPREGRET register is a RAM mapped retained register which will lose it's content after power-cycle. However, it keeps its content after a wakeup from SYSTEMOFF mode. I was using NVIC_SystemReset() function to reset the CPU. Could it be that the register lost its value because of the way CPU is restarted?

Also, should I clear the GPREGRET register before writing any value there? nRF SDK has a function for that (sd_power_gpregret_clr()) but I was unable to find anything similar in <hal/nrf_power.h>.

Cheers,

Bojan.

RE: DFU over USB - nRF52840 running Zephyr

Einar Thorsrud — Mon, 03 May 2021 18:29:06 GMT

Hi Bojan,

The guide you refer to demonstrates the serial recovery feature of MCUBoot, where the DFU process is handled entirely in the bootloader. There is no option to enter DFU by GPREGret there, but you can add it yourself by modifying MCUBoot to check for a magic word in the retention register that you set in your application before resetting. In that case you could look at how this is handled in main() in bootloader\mcuboot\boot\zephyr\main.c and add your logic there.

Regarding the second question, you can reset via mcumgr using "mcumgr reset".

Einar