CC2540 BLE Attribute Size limit

Philip Hopkins

Hello fellow engineers--

I'm trying to write 10 bytes to the simpleGATTProfile characteristic 0x17, UUID: 0xFFF4. I cannot write more than 2 bytes or I get a "Invalid Attribute Value Length" error. I get this error with TI's BTTool and a Bluegiga dongle. I cannot find in the descriptors where I specify an Attribute's size. I can read more than 2 bytes just by changing pLen, but cannot write more than 2 bytes. Is there something I'm missing? i am aware of the 18 or so byte limit of wiring because of the MTU and I know I'm not hitting that limit.

Thanks,

-Phil H.

over 13 years ago

0 GregS over 13 years ago

TI__Expert 6840 points

Hello,

Value4 is a notification characteristic, and is defined without permissions read or write. Notifications are used to push data out from server.

I suspect you are writing to the characteristic configuration. This has size =2.

// Characteristic Value 4
{
{ ATT_BT_UUID_SIZE, simpleProfilechar4UUID },
0,
0,
&simpleProfileChar4
},

// Characteristic 4 configuration
{
{ ATT_BT_UUID_SIZE, clientCharCfgUUID },
GATT_PERMIT_READ | GATT_PERMIT_WRITE,
0,
(uint8 *)simpleProfileChar4Config
},

You can check the handling for read/writes by setting breakpoints in either

simpleProfile_WriteAttrCB

simpleProfile_ReadAttrCB

To enable data push, write a 1 to the characteristic configuration.

BR,

-Greg

0 Philip Hopkins over 13 years ago in reply to GregS

Prodigy 60 points

I typo'd the UUID, it's 0xFFF3, which is Characteristic 3 in which it's write only, with handle #0x17.

Focusing on the question:

How can I change the size to more than 2? If I try to write more than 2, I get an invalid attribute. I don't see where size of 2 is defined in the services in simpleProfileAttrTbl.

0 Philip Hopkins over 13 years ago in reply to Philip Hopkins

Prodigy 60 points

Perhaps I used extended properties?

GATT_CHAR_EXT_PROPS_UUID

Then define somewhere in the extended properties:

GATT_FORMAT_STRUCT

Yes, no?

0 Philip Hopkins over 13 years ago in reply to Philip Hopkins

Prodigy 60 points

Figured it out, there was a len check inside the write handler:

simpleProfile_WriteAttrCB:

if ( offset == 0 )
        {
          if ( len > 1 )
            status = ATT_ERR_INVALID_VALUE_SIZE;
        }
        else
        {
          status = ATT_ERR_ATTR_NOT_LONG;
        }

This status settings was causing the device to choke when getting more than 1 byte

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CC2540 BLE Attribute Size limit