aci_gatt_update_char_value_ext issue

Question

Hello,We are trying to use MTU larger than 24X bytes.The characteristic size set to 483 bytes (CFG_BLE_MAX_ATT_MTU).We tried to use aci_gatt_update_char_value_ext to set the value (as the HCI layer is limited to 255 bytes transfer).aci_gatt_update_char_value_ext called twice (for both MPSs) , first part with 0 offset, and 2nd with 240.First, Update_Type=GATT_CHAR_UPDATE_LOCAL_ONLY;  2nd call with GATT_CHAR_UPDATE_SEND_NOTIFICATION.What happens is that random? number of bytes is sent (80). If we always use GATT_CHAR_UPDATE_SEND_NOTIFICATION proper 480 bytes are sent, but twice (for both offset updates) ... Thanks in advance

STTwo-32 · Accepted Answer

Hello @APort

What I understand, you are looking to send more data. So, I suggest you refer to this description:

1. Modify CFG_BLE_MAX_ATT_MTU to 512 in app_conf.h

2. Call aci_gatt_exchange_config() after connecting in app_ble.c:

tBleStatus status = aci_gatt_exchange_config(BleApplicationContext.BleApplicationContext_legacy.connectionHandle);

3. Change Notify characteristic size in p2p_stm.c:

aci_gatt_add_char(aPeerToPeerContext.PeerToPeerSvcHdle, UUID_TYPE_128, &uuid16,
 CFG_BLE_MAX_ATT_MTU - 3, // [STM]
 CHAR_PROP_NOTIFY, ATTR_PERMISSION_NONE,
 GATT_NOTIFY_ATTRIBUTE_WRITE, /* gattEvtMask */
 10, /* encryKeySize */
 1, /* isVariable: 1 */
 &(aPeerToPeerContext.P2PNotifyServerToClientCharHdle));

4. Change P2PS_STM_App_Update_Char function in p2p_stm.c:

tBleStatus P2PS_STM_App_Update_Char(uint16_t UUID, uint8_t *pPayload) 
{
 tBleStatus result = BLE_STATUS_INVALID_PARAMS;
 switch(UUID)
 {
 case P2P_NOTIFY_CHAR_UUID:
 
 aci_gatt_update_char_value_ext(0x0000,
 aPeerToPeerContext.PeerToPeerSvcHdle,
 aPeerToPeerContext.P2PNotifyServerToClientCharHdle,
 0x00,
 509,
 0,
 243,
 (uint8_t *) pPayload);
 

 aci_gatt_update_char_value_ext(0x0000,
 aPeerToPeerContext.PeerToPeerSvcHdle,
 aPeerToPeerContext.P2PNotifyServerToClientCharHdle,
 0x00,
 509,
 243,
 243,
 (uint8_t *) pPayload + 243);
 
 aci_gatt_update_char_value_ext(0x0000,
 aPeerToPeerContext.PeerToPeerSvcHdle,
 aPeerToPeerContext.P2PNotifyServerToClientCharHdle,
 0x01,
 509,
 486,
 23,
 (uint8_t *) pPayload + 486); 

 break;

 default:
 break;
 }

 return result;
}

5. Modify P2PS_STM_Data_t structure in p2p_stm.h:

typedef struct
{
 uint8_t * pPayload;
 uint16_t Length;
}P2PS_STM_Data_t;

Best Regards.

STTwo-32

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