When I do a sd_ble_gattc_char_value_by_uuid_read I can only get a maximum of 253 bytes.
And when I read more I get a gatt_status of
BLE_GATT_STATUS_ATTERR_INVALID 0x0100 /**< ATT Error: Invalid Error Code. */
and the handler of the uuid characteristics is also incorrect/ not available. (so I can read on with sd_ble_gattc_read)
Is this a bug or can I adjust some parameters so I do not get the error?
In our project we need to read 255 bytes....
# context
In our project we want to read a characteristics of many devices as possible.
fist we did this with de discover datebase ble_db_discovery_start
but reading the characteristics was taking from 800ms to 1500ms.
so we disabled it and did the discovery our self.
we waited for the BLE_GAP_EVT_CONNECTED event.
and after we get a BLE_GAP_EVT_DATA_LENGTH_UPDATE we did a sd_ble_gattc_primary_services_discover (i found this some ware in the forms)
after we got the BLE_GATTC_EVT_PRIM_SRVC_DISC_RSP we did the sd_ble_gattc_char_value_by_uuid_read
This works fine when reading 1 to 253 bytes. and this is why faster. I can read the characteristics in 350ms to 600ms
the ble_gatt_effective_mtu is 512 so I am also not at the maximum bytes.
# Update
I found by lowering the NRF_SDH_BLE_GATT_MAX_MTU_SIZE from 512 to 254. the sd_ble_gattc_char_value_by_uuid_read was successful but incomplete. but now I get the handle witch I can use for the sd_ble_gattc_read to read the rest.
it is not a elegant solution, and I think this takes 50ms more. but still I can get the characteristics now in 400 to 650 ms.
