CC2541: GATT_wRITE , GATT READ Functions - when to use GATT_bm_alloc

Rob Weekly

Intellectual 910 points

Part Number: CC2541
Other Parts Discussed in Thread: CC2640R2F

HI,

Working on a CC2541 based Central device with 3 connections.

So I've been trying to use GATT_ReadMultiCharValue()

I have now solved this, but nothing in the documentation really gave me guidance so I need to clarify operation.

I had originally used a global array for the CHARACTERISTIC HANDLES I wanted to read and just set the req.pHandles to it with current results from the request, but subsequently found this function only seemed to work if I used GATT_bm_alloc() to provide memory for the Handles.

Can anyone explain this operation?

I am also doing single reads using GATT_ReadCharValue(), and don't use the GATT_bm_alloc() for these.

Just need some clarity on what the stack expects here.

Best Regards

Rob

over 5 years ago

0 Clément over 5 years ago

TI__Guru** 101460 points

Hi,

I have assigned an expert to comment.

Best regards,

0 Eirik V over 5 years ago

TI__Guru 56590 points

Hello Rob,

The attReadMultiReq_t type contain a pointer to the actual attribute handles, but GATT_ReadMultiCharValues expect this to be in the form of a allocated buffer that is used to build the complete command. GATT_bm_alloc will allocate space for the handles and the opode (before the handles) for the stack to use. The hedaer adjustment is handled by GATT_bm_alloc.

/**
 * Read Multiple Request format.
 */
typedef struct
{
  uint8 *pHandles;  //!< Set of two or more attribute handles (4 to ATT_MTU_SIZE-1) - must be first field
  uint8 numHandles; //!< Number of attribute handles
} attReadMultiReq_t;

An example for how to use it on CC2640R2F:

https://e2e.ti.com/support/wireless-connectivity/bluetooth/f/538/p/799994/2964662#2964662

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CC2541: GATT_wRITE , GATT READ Functions - when to use GATT_bm_alloc