requestAttMtu gets NRF_ERROR_INVALID_PARAM

[dwBreezi]

I am working on a linux vm 16.04 and playing with the pc-ble-drive-js library.  I recently got the board up and running and started looking at the heart_rate_collector example to get my bearings.  I already have a solution with our device written in python but I would like to be able to work with larger packets and thought the nordic solution might work better.  I modified the heart_rate_collector to use my device and once it is ready to take a sample I pass in a requestAttMtu call.  I receive the NRF_ERROR_INVALID_PARAM error code, but I am not sure what is being passed in in error since both my connection handle and mtu value are correct.  Below is some output with my device information and the error.  Let me know if more information will be useful.

ble device: NRF52832
device: /dev/ttyACM0
version: v3

Device {
_instanceId: 'D8:34:CF:9D:7B:38.0',
_address: 'D8:34:CF:9D:7B:38',
_addressType: 'BLE_GAP_ADDR_TYPE_RANDOM_STATIC',
adData: {},
name: null,
_role: 'peripheral',
services: [],
flags: [],
scanResponse: null,
connected: true,
rssi: null,
txPower: null,
_connectionHandle: 0,
minConnectionInterval: 7.5,
maxConnectionInterval: 7.5,
slaveLatency: 0,
connectionSupervisionTimeout: 4000,
paired: false,
ownPeriphInitiatedPairingPending: false }

Connection handle is 0 mtu is 222
Current mtu 247
MTU Error Error occured when requesting MTU exchange. Errorcode: NRF_ERROR_INVALID_PARAM (0x7)

Error during requestAttMtu [object Object]
Error {
message: 'Failed to request att mtu: Error occured when requesting MTU exchange. Errorcode: NRF_ERROR_INVALID_PARAM (0x7)\n',
description: undefined }

Thanks,

Derek Wooters

[dwBreezi]

Thanks for taking a look Einar.  I passed in 222 as my mtu size I am requesting.  It is under the current mtu of 247 negotiated and I wanted to use a unique one for testing purposes.  

[Einar Thorsrud]

I see. Then that could be the problem. One of the requirements is that the supplied mtu value must be equal to Server RX MTU size given in sd_ble_gatts_exchange_mtu_reply if an ATT_MTU exchange has already been performed in the other direction. You will get a NRF_ERROR_INVALID_PARAM if that is not the case (See SoftDevice API documentation for sd_ble_gattc_exchange_mtu_request() for details).