Increase MTU size blinky example

[MarcoTull]

Hi all,

It could be something simple, but I cant get it yet.

If I increase: NRF_BLE_GATT_MAX_MTU_SIZE from 23 to 247 on sdk_config.h attr_char_value.max_len inside my characterstic to 244 on the service file params.p_len = 244;

when I call sd_ble_gatts_hvx() I cant see nothing being pushed from my peripheral are these the correct steps to increase the MTU size and send biggers packets thought BLE? or do I have to do some extra steps?

Thanks Marco

[Hung Bui]

Have you checked if sd_ble_gatts_hvx() returns success ? Have you checked if your request for longer MTU accepted by the peer device ? And it's used in the network ?

[MarcoTull]

Hi Hung, I checked the sd_ble_gatts_hvs() and it is returning err code 12291 when I increase the MTU size on my periphera. I also made NRF_BLE_GATT_MAX_MTU_SIZE from 23 to 247 on sdk_config.h on my central device (my peer device).

Using a Sniffer I got the following when the sd_ble_gatts_hvx() is called my peripheral send a ATT_exchange_MTU_Req opcode 0x02 ClientRxMTU 0x00F7 to the central and the central response is ATT_exchange_MTU_Rsp Opcode 0x03 ServerRxMTU 0x0017

[Hung Bui]

12291 = 0x3003 = BLE_ERROR_INVALID_ATTR_HANDLE , seems that you used wrong character handle ID. And from your sniffer trace, it doesn't seems the central support long ATT MTU here.

[MarcoTull]

when I call the sd_ble_gatts_hvx() with a MTU size < 23 I dont get that error code. is it possible central is causing the issue? because it does not support long ATT MTU? how can I increase it size in the central I could not find references for this

thanks

[Hung Bui]

I don't think the central can cause that error. It's pretty strange. Could you reproduce this issue with any of our example and send me the code so I can test here ?

Which central are you using ? If it's not Nordic (a phone for example) , I don't think it's possible to change the MTU.