nRF52 DK ble_app_cscs example "Change MTU size issue"

[silverzero]

Hi I want to change MTU size cuz I want to send  more

sdk_config.h
// <i> Requested BLE GAP data length to be negotiated.

#ifndef NRF_SDH_BLE_GAP_DATA_LENGTH
#define NRF_SDH_BLE_GAP_DATA_LENGTH 247
#endif

// <o> NRF_SDH_BLE_PERIPHERAL_LINK_COUNT - Maximum number of peripheral links. 
#ifndef NRF_SDH_BLE_PERIPHERAL_LINK_COUNT
#define NRF_SDH_BLE_PERIPHERAL_LINK_COUNT 1
#endif

// <o> NRF_SDH_BLE_CENTRAL_LINK_COUNT - Maximum number of central links. 
#ifndef NRF_SDH_BLE_CENTRAL_LINK_COUNT
#define NRF_SDH_BLE_CENTRAL_LINK_COUNT 0
#endif

// <o> NRF_SDH_BLE_TOTAL_LINK_COUNT - Total link count. 
// <i> Maximum number of total concurrent connections using the default configuration.

#ifndef NRF_SDH_BLE_TOTAL_LINK_COUNT
#define NRF_SDH_BLE_TOTAL_LINK_COUNT 1
#endif

// <o> NRF_SDH_BLE_GAP_EVENT_LENGTH - GAP event length. 
// <i> The time set aside for this connection on every connection interval in 1.25 ms units.

#ifndef NRF_SDH_BLE_GAP_EVENT_LENGTH
#define NRF_SDH_BLE_GAP_EVENT_LENGTH 260
#endif

// <o> NRF_SDH_BLE_GATT_MAX_MTU_SIZE - Static maximum MTU size. 
#ifndef NRF_SDH_BLE_GATT_MAX_MTU_SIZE
#define NRF_SDH_BLE_GATT_MAX_MTU_SIZE 247
#endif

// <o> NRF_SDH_BLE_GATTS_ATTR_TAB_SIZE - Attribute Table size in bytes. The size must be a multiple of 4. 
#ifndef NRF_SDH_BLE_GATTS_ATTR_TAB_SIZE
#define NRF_SDH_BLE_GATTS_ATTR_TAB_SIZE 1408
#endif

// <o> NRF_SDH_BLE_VS_UUID_COUNT - The number of vendor-specific UUIDs. 
#ifndef NRF_SDH_BLE_VS_UUID_COUNT
#define NRF_SDH_BLE_VS_UUID_COUNT 0
#endif

// <q> NRF_SDH_BLE_SERVICE_CHANGED  - Include the Service Changed characteristic in the Attribute Table.
 

#ifndef NRF_SDH_BLE_SERVICE_CHANGED
#define NRF_SDH_BLE_SERVICE_CHANGED 0
#endif












/////////////////ble_cscs.c
#define MAX_CSCM_LEN (BLE_GATT_ATT_MTU_DEFAULT - OPCODE_LENGTH - HANDLE_LENGTH)









///////////////ble_gatt.h

/** @addtogroup BLE_GATT_DEFINES Defines
 * @{ */

/** @brief Default ATT MTU, in bytes. */
#define BLE_GATT_ATT_MTU_DEFAULT          23

/**@brief Invalid Attribute Handle. */
#define BLE_GATT_HANDLE_INVALID            0x0000

/**@brief First Attribute Handle. */
#define BLE_GATT_HANDLE_START              0x0001

/**@brief Last Attribute Handle. */
#define BLE_GATT_HANDLE_END                0xFFFF

/** @defgroup BLE_GATT_TIMEOUT_SOURCES GATT Timeout sources
 * @{ */
#define BLE_GATT_TIMEOUT_SRC_PROTOCOL      0x00  /**< ATT Protocol timeout. */
/** @} */

30bytes.

Now I'd identified only 20 bytes of data being transferred.

I changed the MTU SIZE, but it does not become advertising. This is my code. What parts do I have to change?

Or, can't I change the MTU size in the cscs example?

[Sigurd]

Hi,

By default you should be able to encode and send all needed cycling speed and cadence measurements that is part of the CSC characteristic in 20 bytes.

If for some reason 20 bytes is not enough in your use-case, you could try to change the MAX_CSCM_LEN in ble_cscs.c to this:

#define MAX_CSCM_LEN  (NRF_SDH_BLE_GATT_MAX_MTU_SIZE - OPCODE_LENGTH - HANDLE_LENGTH)    /**< Maximum size of a transmitted Cycling Speed and Cadence Measurement. */

[silverzero]

Hi, Yes I did that but It doesn't work. 

I change 
#define MAX_CSCM_LEN (BLE_GATT_ATT_MTU_DEFAULT - OPCODE_LENGTH - HANDLE_LENGTH)
//BLE_GATT_ATT_MTU_DEFAULT = 23

to 

#define MAX_CSCM_LEN (33 - OPCODE_LENGTH - HANDLE_LENGTH)

[Sigurd]

Seems to work fine here. But you need to allocate more RAM to the SoftDevice after applying this change.