Example code to write to UICR

[rmarques]

I am trying to store data to the UICR using SDK16, mesh SDK 4.2.0 and the nRF52840 chip.

I want to write to the UICR once on runtime and never again. To avoid messing with the softdevice, I am trying to write to the UICR before calling ble_stack_init() and after __LOG_INIT to get logs working.

This is the code:

NRF_NVMC->CONFIG = NVMC_CONFIG_WEN_Wen;
while (NRF_NVMC->READY == NVMC_READY_READY_Busy){}

uint32_t * consumer0 = (uint32_t *) 0x10001080;
*consumer0 = 0x00000005;

NRF_NVMC->CONFIG = NVMC_CONFIG_WEN_Ren;
while (NRF_NVMC->READY == NVMC_READY_READY_Busy){}
__LOG(LOG_SRC_APP, LOG_LEVEL_INFO, "%d\n", *consumer0);

NVIC_SystemReset();

So we put the NVMC in Write enable, wait for it to be ready, write to consumer0, put it in Read enable, wait for it to be ready and reset the device. I can see 5 logged to Segger console.

Then I comment what I don't need:

//NRF_NVMC->CONFIG = NVMC_CONFIG_WEN_Wen;
//while (NRF_NVMC->READY == NVMC_READY_READY_Busy){}

uint32_t * consumer0 = (uint32_t *) 0x10001080;
//*consumer0 = 0x00000005;

//NRF_NVMC->CONFIG = NVMC_CONFIG_WEN_Ren;
//while (NRF_NVMC->READY == NVMC_READY_READY_Busy){}
__LOG(LOG_SRC_APP, LOG_LEVEL_INFO, "%d\n", *consumer0);

//NVIC_SystemReset();

And I see -1 logged to Segger console, meaning the flash still has the 0xFFFF on that position. I can confirm it on Segger Memory explorer that 10001080 is never filled with the data I wanted. Am I doing something wrong?

[Learner]

Thank you rmarques.

We are not using MeshSDK and I know nothing about it. 

Using UICR seems like a very simple way of achieving what we want (if it works!). I am going to persevere with UICR a little longer before I go to plan B.

Kind regards

Mohamed

[Einar Thorsrud]

Hi Mohamed,

Generally, when Access port protection is enabled, the only way to recover is to do a full chip erase (ERASE ALL), and that will erase the UICR. So the only way to avoid this is to ensure that access port protection is not enabled in the first place.

The code snippet you have here works with the latest revision of the ICs, which improved APPROTECT. Can you first double check which IC revision you are using so that you know this code matches the revision you have? Assuming it does and there are no bugs in this code (I might overlook something and I dont know your system_WriteDebugPortAccess() function), you will always have to do a recover / erase all if your CONFIG_DEBUG_PORT_ACCESS is false/0.

[Learner]

Hi Thorsrud,

Einar Thorsrud said:

So the only way to avoid this is to ensure that access port protection is not enabled in the first place.

I use two versions of prj.conf, prj_debug.conf where CONFIG_DEBUG_PORT_ACCESS=y and prj_release.conf where CONFIG_DEBUG_PORT_ACCESS=n.

Einar Thorsrud said:

you will always have to do a recover / erase all if your CONFIG_DEBUG_PORT_ACCESS is false/0.

So, in debug mode I should NOT be experiencing this problem, right?

Also, isn't the whole purpose of the access port protection is to make sure it is enabled before product deployment?

Einar Thorsrud said:

Can you first double check which IC revision you are using so that you know this code matches the revision you have?

We are currently using a mixture of N52833 QDAAB0 and QDAAA0 but ultimately we will be using only revision QDAAB0.

Einar Thorsrud said:

Assuming it does and there are no bugs in this code (I might overlook something and I dont know your system_WriteDebugPortAccess() function)

Here is my function

static void system_WriteDebugPortAccess(uint32_t value)
{
    /* Allow UICR access */
    NRF_NVMC->CONFIG = NVMC_CONFIG_WEN_Wen;
    while (NRF_NVMC->READY == NVMC_READY_READY_Busy) { }

    /* Set new value for HW protection of AP */
    NRF_UICR->APPROTECT = value;

    /* Disallow UICR access */
    NRF_NVMC->CONFIG = NVMC_CONFIG_WEN_Ren;
    while (NRF_NVMC->READY == NVMC_READY_READY_Busy) { }

    /* Reboot to take new UICR values */
    system_Reset();
}

Thank you.

Kind regards

Mohamed

[Einar Thorsrud]

Hi Mohamed,

Learner said:

So, in debug mode I should NOT be experiencing this problem, right?

I do not know everything you do, but yes: as long as debug port access is enabled, then you can erase and write specific sectors and do not need to do a full chip erase.

Learner said:

Also, isn't the whole purpose of the access port protection is to make sure it is enabled before product deployment?

Yes it is. But that also means that debug access is blocked, and to enable it you must do an ERASE ALL (recover), which also erases UICR.

Learner said:

We are currently using a mixture of N52833 QDAAB0 and QDAAA0 but ultimately we will be using only revision QDAAB0.

I see. The code snippet you have seems to match QDAAB0, which has the improved access port mechanism (IN-149). With this debugging is disabled by default and you need to disable it by writing to UICR and also writing to  NRF_APPROTECT->DISABLE on every boot. If not, a full erase is needed to be able to debug again.

Note that it is also so that the only way to erase UICR is to erase the whole flash, so if the UICR is "suddenly" erased it is because the tools you use for some reason do an erase all. The question is why. Can you start by reading data from UICR to see if debug access is enabled and the data is still there? then what exactly do you do when the UICR is erased by the debugger?

[Learner]

Hi Thorsrud,

Before I try what you suggested I would like you to clarify the statement below.

dgerman said:

write to flash can only reset bits. It is necessary to erase flash to set it to FFFFFFF

Is the above statement from dgerman correct?

I see you are not erasing flash in the example code you shared earlier with rmarques.

Please clarify.

Thank you.

Kind regards

Mohamed