Bluetooth: Characteristic Value Showing up as N/A on nRF Connect App

[SarikaK]

I'm unable to load values into characteristics—they show up as N/A on the nRF Connect app. I tried to enable notifications using the Client Characteristic Configuration, but when I click on the second arrow button (which I think is for enabling notifications, but I could be wrong), I am getting an error that says "Reading is not permitted". I thought I had set the necessary read permissions, but is there something I need to fix here?

This is the function which is passed the value that I want to load into the characteristic:

What I see in the app:

[Susheel Nuguru]

What is AFE_GATT_PERM_DEFAULT? are you sure if there are read permissions there?

[SarikaK]

My understanding is that AFE_GATT_PERM_DEFAULT should set the default GATT permissions for both read and write:

[Susheel Nuguru]

Seems right to have Read and Write permissions on this. Can you give give me your project to test for me to reproduce this on my desk?  I will have to test this on Monday if you attach your project here.

[SarikaK]

peripheral_nfc_pairing.zip

Thank you!

[SarikaK]

Just wanted to follow up on this!

[Susheel Nuguru]

I am sorry Sarika, Did not reproduce the issue yet, 

I will spend time tomorrow to reproduce this and if I manage to reproduce it, it will be easy to give a workaround/fix.

[Susheel Nuguru]

sorry for testing this a bit late Sarika, 

I see no issues with the read permissions testing this on iPhone14 with nRF connect for mobile app.

scratch that ..I am able to reproduce that it is not able to read the characteristic when pressing the down arrow. I will look into it and see if it is missing any permissions.

[Susheel Nuguru]

Just realized that you have not implemented the gatt read function for reading the attribute. Please fix your service definition as below 

static ssize_t read_nfc_feature(struct bt_conn *conn,
				const struct bt_gatt_attr *attr, void *buf,
				uint16_t len, uint16_t offset)
{
	return bt_gatt_attr_read(conn, attr, buf, len, offset, NULL, 0);
}

/* Sine Wave Service Declaration */
BT_GATT_SERVICE_DEFINE(afe_svc,
	BT_GATT_PRIMARY_SERVICE(BT_UUID_AFE_DATA),
	BT_GATT_CHARACTERISTIC(BT_UUID_SINE_WAVE,
				BT_GATT_CHRC_READ | BT_GATT_CHRC_NOTIFY,
				BT_GATT_PERM_READ, read_nfc_feature, NULL,
				NULL),
	BT_GATT_CCC(afe_ccc_cfg_changed,
			 AFE_GATT_PERM_DEFAULT),
);

This should allow your app to read the attribute from nrf connect app.