Unexpected return value when calling sd_ble_gatts_hvx() when notifications are not enabled

[m.wagner]

This issue concerns code using Softdevice S132 v6.1.1. v5.0.0. I did not test with any other version.

From the documentation of sd_ble_gatts_hvx in ble_gatts.h, I expect that the return value when calling this function while notifications are disabled for the characteristic in question is NRF_ERROR_INVALID_STATE.

Instead, the function returns BLE_ERROR_NOT_ENABLED, which suggests that the softdevice is not enabled, but this is of course not the case because the device in question is connected when the issue arises.

[AndreasF]

Hi.

Have you enabled the SoftDevice? BLE_ERROR_NOT_ENABLED will only be returned if the SoftDevice is not enabled.

Best regards,

Andreas

[m.wagner]

AndreasF said:

Have you enabled the SoftDevice?

As I mentioned in my initial question, the softdevice is enabled. Even a BLE connection has been established at the point that issue arises, so the behaviour of this call is indeed not as documented.

I just assume that there was a simple mishap when implementing the function, "BLE_ERROR_NOT_ENABLED" by itself does sound like the right error to return when notifications are "not enabled"... ;-)

[m.wagner]

Hi,

Unfortunately I haven't gotten around looking into it more closely, but I noticed that I mixed up two projects. This issue specifically concerns S132 v5.0.0 and not v6.1.1 as originally mentioned!

Also, the product has actually been in production for some time and is not still in development.

Regards,

-mike

[AndreasF]

Hi.

It's the same check performed for v6.1.1 as for v5.0.0, so it should not be different as far as I know.

Best regards,

Andreas

[m.wagner]

Hi Andreas,

AndreasF said:

Could you help me reproduce the issue? Perhaps share your project? I can make the ticket private if you like :-)

I finally managed to reproduce the issue for you. I don't even have to provide code, the Nordic SDK provides the example directly.

Steps to reproduce:

1. Download SDK 15.2.0
2. Flash the associated softdevice onto an nRF52 DK (S132 v6.1.0)
3. Build and flash the exmple "ble_peripheral\ble_app_blinky"
4. Start the debugger and set a breakpoint in main.c, function button_event_handler(), in the if-block on line 497:
   

   if (err_code != NRF_SUCCESS &&
                   err_code != BLE_ERROR_INVALID_CONN_HANDLE &&
                   err_code != NRF_ERROR_INVALID_STATE &&
                   err_code != BLE_ERROR_GATTS_SYS_ATTR_MISSING)

5. Connect to the peripheral with e.g. nRF Connect.
6. Press Button 1 on the nRF52 DK.
7. When you inspect the contents of the err_code variable in the debugger, you will notice that the value reads 0x3401, which corresponds to BLE_ERROR_NOT_ENABLED and is documented in ble_err.h as indicating that "sd_ble_enable has not been called."

Best regards,

-mike

[AndreasF]

Hi.

I've give you a reply tomorrow, I've been quite busy today, sorry.

Best regards,

Andreas

[AndreasF]

Hi.

The error you see is not BLE_ERROR_NOT_ENABLED, but BLE_ERROR_GATTS_SYS_ATTR_MISSING.

We can first take a look at the math for the two different definitions:

NRF_ERROR_STK_BASE_NUM = 0x3000 in the SDK

BLE_ERROR_NOT_ENABLED = NRF_ERROR_STK_BASE_NUM + 0x001 = 0x3001

BLE_ERROR_GATTS_SYS_ATTR_MISSING = NRF_GATTS_ERR_BASE + 0x001 = NRF_ERROR_STK_BASE_NUM + 0x400 + 0x001 = 0x3401

Also checked that this is the value by debugging:

Can also see that sd_ble_enabled returns 0x8 which is invalid state (NRF_ERROR_INVALID_STATE):

So I'm pretty confident that the error is BLE_ERROR_GATTS_SYS_ATTR_MISSING, and the solution to handle this error is described here.

Best regards,

Andreas