Temporary GATT characteristic update

[Sarah]

Hello,

I am adding an extra characteristic (of 6 bytes) into one of the services that exist in the default beacon app. Then I try to update this characteristic using master control app, but after I disconnect the beacon and connect back to it, the value is not there anymore. I'm not sure what to do to fix this. Any help would be appreciated.

Thanks!

[Hung Bui]

@Sarah: Which beacon example did you base on ? Usually the beacon should not have any service or characteristic, because it's a beacon, non-connectable.

Have you make sure you have read and write permission open on the characteristic ? You should try to read the value back after you write. Also make sure the device doesn't reset after you disconnect.

[Sarah]

I'm using the ble_app_beacon_s110_pca20006 example, where when you press sw2 button the beacon switches to config mode. I looked at how other readable/writable characteristics are added and tried to implement the same. This is the function I created to add a new characteristic:

static uint32_t beacon_mac_char_add(ble_bcs_t * p_bcs, const ble_bcs_init_t * p_bcs_init) {

ble_gatts_char_md_t char_md; ble_gatts_attr_t attr_char_value; ble_uuid_t ble_uuid; ble_gatts_attr_md_t attr_md;

memset(&char_md, 0, sizeof(char_md));

char_md.char_props.read   = 1;
char_md.char_props.write  = 1;
char_md.p_char_user_desc  = NULL;
char_md.p_char_pf         = NULL;
char_md.p_user_desc_md    = NULL;
char_md.p_cccd_md         = NULL;
char_md.p_sccd_md         = NULL;

ble_uuid.type = p_bcs->uuid_type;
ble_uuid.uuid = BCS_UUID_BEACON_MAC_CHAR;

memset(&attr_md, 0, sizeof(attr_md));

BLE_GAP_CONN_SEC_MODE_SET_OPEN(&attr_md.read_perm);
BLE_GAP_CONN_SEC_MODE_SET_OPEN(&attr_md.write_perm);

attr_md.vloc       = BLE_GATTS_VLOC_STACK;
attr_md.rd_auth    = 0;
attr_md.wr_auth    = 0;
attr_md.vlen       = 0;

memset(&attr_char_value, 0, sizeof(attr_char_value));

attr_char_value.p_uuid       = &ble_uuid;
attr_char_value.p_attr_md    = &attr_md;
attr_char_value.init_len     = BCS_DATA_MAC_LEN;
attr_char_value.init_offs    = 0;
attr_char_value.max_len      = BCS_DATA_MAC_LEN;
attr_char_value.p_value      = &p_bcs_init->p_beacon->data.mac_address[6];

return sd_ble_gatts_characteristic_add(p_bcs->service_handle, &char_md,
                                           &attr_char_value,
                                           &p_bcs->beacon_mac_char_handles);

}

I defined BCS_UUID_BEACON_MAC_CHAR to be 0x1522, as I didn't notice it being used in the code, and BCS_DATA_MAC_LEN is 6.

[Hung Bui]

@Sarah: If you have a look at the BLE_GAP_EVT_DISCONNECTED event in on_ble_evt() in main.c you can find that we will do a beacon_reset() after we get disconnected. It's normal because it's config mode when connected so we should reset to be back to normal mode. However, the value of your characteristic is stored on RAM. So if you don't store your characteristic value and restore it when restart in config mode, the value will be lost.

I think this explained what you described.

[Sarah]

Thanks Hung, I see what you mean. How do I restore things on RAM, how should I modify the sample app for that?

[Hung Bui]

@Sarah: Sorry that my answer was not clear. You should store your data on flash, not RAM. To be able to store some data on flash, you should use pstorage library.

Please have a look at beacon_write_handler() where we use pstorage_store() to store beacon's configuration data to flash. You can either modify the beacon_data_t structure or create your own pstorage module/block to store your data.