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128bit UUID's and GATT characteristic value length

Chris Cowdery
Prodigy 190 points

Hi All,

 I am trying to discover the implications of using 128bit UUID's. I believe that the 16 bytes of the UUID will consume a significant part of the message payload, from ATT_MTU_SIZE = 23.

I have looked at these two threads:

It seems that there is an issue when your characteristic value size goes about 19. If I have 128bit UUID's, then the UUID is 14 bytes longer than usual. Am I then reduced to a 5 byte characteristic.

The standard talks about blobs, and the GATT API appears to support this. For example, the callback to read an attribute is:

simpleProfile_ReadAttrCB( uint16 connHandle, gattAttribute_t *pAttr,  uint8 *pValue, uint8 *pLen, uint16 offset, uint8 maxLen )

which suggests that using the offset, a longer attribute can be read.

Can anybody confirm that the appropriate multiple callbacks will be made if for example I had a 10 byte characteristic and a 128bit UUID?

I need to find this out early on so I can design my service accordingly.

Thanks,

Chris.