5 years, 3 months ago.

Increase maximum MTU size for write in a GATT Characteristic with nRF52-DK

Hi,

Im trying to write into a GATT Characteristic, but as we know by default we only have 20 bytes available. How can I increase this value using the nRF52-DK board and Mbed? I tried using the GATTCharacteristic generic class, but the GATT Server crashes if I send more than 20 bytes.

This is my custom GATT Server code:

1. ifndef BLE_TOF_SERVICE_H
2. define BLE_TOF_SERVICE_H

1. include "ble/BLE.h"

class TOFService { public: const static uint8_t TOF_CHAR_ARRAY_SIZE = 100; const static uint16_t CUSTOM_TOF_SERVICE_UUID = 0xA000; const static uint16_t TOF_CHAR_WRITE_CHARACTERISTIC_UUID = 0xA001;

TOFService(BLE& _ble) : ble(_ble), writeCharArrayCharacteristic(TOF_CHAR_WRITE_CHARACTERISTIC_UUID, writeValue) writeCharArrayCharacteristic(TOF_CHAR_WRITE_CHARACTERISTIC_UUID, writeBuffer, 1, 100, GattCharacteristic::BLE_GATT_CHAR_PROPERTIES_WRITE | GattCharacteristic::BLE_GATT_CHAR_PROPERTIES_WRITE_WITHOUT_RESPONSE | GattCharacteristic::BLE_GATT_CHAR_PROPERTIES_EXTENDED_PROPERTIES) { static bool serviceAdded = false; /* We should only ever need to add the information service once. */ if (serviceAdded) { return; }

GattCharacteristic *charTable[] = {&writeCharArrayCharacteristic};

GattService TOFService(CUSTOM_TOF_SERVICE_UUID, charTable, sizeof(charTable) / sizeof(GattCharacteristic *));

ble.gattServer().addService(TOFService); serviceAdded = true; }

GattAttribute::Handle_t getValueHandle() const { return writeCharArrayCharacteristic.getValueHandle(); }

private: BLE& ble;

uint8_t writeBuffer[TOF_CHAR_ARRAY_SIZE];

WriteOnlyArrayGattCharacteristic<uint8_t, sizeof(writeBuffer)> writeCharArrayCharacteristic; GattCharacteristic writeCharArrayCharacteristic; };

1. endif /* #ifndef BLE_TOF_SERVICE_H*/

Thank you very much.