STM BlueNRG-MS Max Characteristic length

Question

My general understanding is that the BLE standard supports characteristics with a lenght of up to 512 bytes. I'm using the BlueNRG-MS chip from STM but there the function call to add a characteristic has a uint8_t value for the length parameter

tBleStatus aci_gatt_add_char(uint16_t serviceHandle,
                 uint8_t charUuidType,
                 const uint8_t* charUuid, 
                 uint8_t charValueLen, 
                 uint8_t charProperties,
                 uint8_t secPermissions,
                 uint8_t gattEvtMask,
                 uint8_t encryKeySize,
                 uint8_t isVariable,
                 uint16_t* charHandle);

So this would allow only a maximum characteristic length of 255 bytes. According to this document the stack itself supports 2 bytes with FW 7.2 or higher. I have 7.23 so this should be fine but I cannot find any reference or example of a BlueNRG-MS middleware that would support a call with charValueLen of type uint16_t. I also downloaded the latest STSW-BLUENRG-DK and the examples also only support uint8_t charValueLen.

Answer 1

Yes, it supports charValueLen with uint16_t too. Sample function would be as followed:

tBleStatus aci_gatt_add_char(uint16_t serviceHandle,
                         uint8_t charUuidType,
                         const uint8_t* charUuid, 
                         uint16_t charValueLen, 
                         uint8_t charProperties,
                         uint8_t secPermissions,
                         uint8_t gattEvtMask,
                         uint8_t encryKeySize,
                         uint8_t isVariable,
                         uint16_t* charHandle)
{
  struct hci_request rq;
  gatt_add_serv_rp resp;
  uint8_t buffer[26];
  ... // code omitted w/o needing modification

  Osal_MemCpy(buffer + indx, charUuid, uuid_len);
  indx +=  uuid_len;

  charValueLen = htobs(charValueLen);
  Osal_MemCpy(buffer + indx, &charValueLen, 2);
  indx += 2;

  buffer[indx] = charProperties;
  indx++;
  ... // code omitted w/o needing modification
}