Setting Custom Gatt characteristic data.

[Thomas]

Hi,

I want to set a custom value to my Gatt characteristic value. I can do this by writing to the characteristic in my app or the NRF_connect application. 

What I want to do is based on an event or the data I receive to change the GATT characteristic data for my app to receive. I tried using this code which, did not change the data.

//err_code = ble_cus_custom_value_update(p_cus, p_ble_evt,m_custom_value);
//APP_ERROR_CHECK(err_code);
//I pass in a fixed value for testing into m_custom_value

uint32_t ble_cus_custom_value_update(ble_cus_t * p_cus, ble_evt_t const * p_ble_evt, uint8_t custom_value)
{
    NRF_LOG_INFO("In ble_cus_custom_value_update. \r\n"); 
    if (p_cus == NULL)
    {
        return NRF_ERROR_NULL;
    }

    uint32_t err_code = NRF_SUCCESS;
    ble_gatts_value_t gatts_value;

    // Initialize value struct.
    memset(&gatts_value, 0, sizeof(gatts_value));

    gatts_value.len     = sizeof(uint8_t);
    gatts_value.offset  = 0;
    gatts_value.p_value = &custom_value;

    // Update database.
    err_code = sd_ble_gatts_value_set(p_cus->conn_handle,
                                      p_cus->custom_value_handles.value_handle,
                                      &gatts_value);
    if (err_code != NRF_SUCCESS)
    {
        return err_code;
    }

    // Send value if connected and notifying.
    if ((p_cus->conn_handle != BLE_CONN_HANDLE_INVALID)) 
    {
        ble_gatts_hvx_params_t hvx_params;

        memset(&hvx_params, 0, sizeof(hvx_params));

        hvx_params.handle = p_cus->custom_value_handles.value_handle;
        hvx_params.type   = BLE_GATT_HVX_NOTIFICATION;
        hvx_params.offset = gatts_value.offset;
        hvx_params.p_len  = &gatts_value.len;
        hvx_params.p_data = gatts_value.p_value;

        err_code = sd_ble_gatts_hvx(p_cus->conn_handle, &hvx_params);
    }
    else
    {
        err_code = NRF_ERROR_INVALID_STATE;
    }


    return err_code;
}

What I need to know is how to update this data value so I can transfer useful data between the two devices (mobile application and nordic board).

Note I am trying to do this within my GATT connection itself.

Note using SDK15 , PCA10056 NRF52840-dk Segger,

Thanks

[Sigurd]

Hi,

What I want to do is based on an event or the data I receive to change the GATT characteristic data for my app to receive. I tried using this code which, did not change the data.

 So you are calling ble_cus_custom_value_update() to update the value? but the value is not updated? Did you get any errors codes returned from ble_cus_custom_value_update() ?

[Thomas]

Thanks for your response. Sorry I forgot to add on calling the function(from within my gatt connection code). It returns an error: 3400. 0r 0x00003400. Just to add some context I am receiving a command from a GATT connection via a mobile application which if passed(Correct command) i then output some text via uart and call the ble_cus_custom_value_update();

I am not however, sure why this crash occurs. Thanks

[Thomas]

Also another question(Completely non related). I found a post you commented on about timing and calender's. I have downloaded the example and it works. But, can I add this functionality to my code as in the comments it says to add soft device support. If my GATT connection is maintained e.g. I'm transferring data between two devices; will the date still increment each second?

Thanks,

Post is here: https://devzone.nordicsemi.com/f/nordic-q-a/25086/local-time-utc-and-timezones. With a link to the github.

[Sigurd]

Did you add the service / characteristic like this ?

https://github.com/bjornspockeli/custom_ble_service_example/blob/SDK_v15.0.0/ble_cus.c#L198

Thomas said:

It returns an error: 3400. 0r 0x00003400

 This is BLE_ERROR_GATTS_INVALID_ATTR_TYPE .  

If you call sd_ble_gatts_hvx() and the return error code is:

* @retval ::BLE_ERROR_GATTS_INVALID_ATTR_TYPE Invalid attribute type(s) supplied, only characteristic values may be notified and indicated.

Then I think either hvx_params.handle is wrong (maybe it's not the correct handle to the characteristic that can notify values), or the handle you are using is pointing to a characteristic that don't support notifications (char_props.notify).

[Thomas]

I believe I added the service and characteristic properly. I did follow that tutorial but here is my init code non the less. 

The data for p_cus and the event is passed in from the on_write statement inside of the gatt connection itself. 

uint32_t ble_cus_init(ble_cus_t * p_cus, const ble_cus_init_t * p_cus_init)
{
    //Init statemachine for reading the commands

    CMD_BLE_STATE_VALUE = CMD_BLE_STATE_START;//Move to start state
    CMD_STARTED = true;

    if (p_cus == NULL || p_cus_init == NULL)
    {
        return NRF_ERROR_NULL;
    }

    uint32_t   err_code;
    ble_uuid_t ble_uuid;

    // Initialize service structure
    //p_cus->evt_handler               = p_cus_init->evt_handler;
    p_cus->conn_handle               = BLE_CONN_HANDLE_INVALID;
    //p_cus->conn_handle               = BLE_CONN_HANDLE_INVALID;

    // Add Custom Service UUID
    ble_uuid128_t base_uuid = {CUSTOM_SERVICE_UUID_BASE};
    err_code =  sd_ble_uuid_vs_add(&base_uuid, &p_cus->uuid_type);
    VERIFY_SUCCESS(err_code);
    
    ble_uuid.type = p_cus->uuid_type;
    ble_uuid.uuid = CUSTOM_SERVICE_UUID;

    // Add the Custom Service
    err_code = sd_ble_gatts_service_add(BLE_GATTS_SRVC_TYPE_PRIMARY, &ble_uuid, &p_cus->service_handle);
    if (err_code != NRF_SUCCESS)
    {
        return err_code;
    }
    // Add Custom Value characteristic
    return custom_value_char_add(p_cus, p_cus_init);
}

You are correct though it is sd_ble_gatt_hvx that is the issue. So how can I write to it? Do I change it from having notifications enabled to something that is not?

[Sigurd]

1) Could you post the code for the place where you call ble_cus_custom_value_update()?

2) Can you post your ble_cus.c code ?

[Thomas]

I call the ble_cus_custom_value_update() within my ble_cus.c code.

I do it within a statemachine that handles processing of incoming data. This incoming data is handled via two statemachines. Process_Command and process_selected_value. Within this I have a help command that if run prints out help info is: . Then runs the command( this is for testing). Below is my code:

#include "sdk_common.h"
#include "ble_srv_common.h"
#include "ble_cus.h"
#include <string.h>
#include "nrf_gpio.h"
#include "boards.h"
#include "nrf_log.h"

bool CMD_STARTED = false;
bool Print_log_enabled = false;//If ==1 enable printing log if == 0 dissabled
bool Processing_Commands = false;
static uint8_t m_custom_value = 77;
//Statemachine for GATT commands
enum
{
    CMD_BLE_STATE_START,
    CMD_BLE_STATE_STOP,
    CMD_BLE_STATE_SELECT_COMMAND,
    CMD_BLE_STATE_UART_LOGGING,
    CMD_BLE_STATE_SD_LOGGING,
    CMD_BLE_STATE_READ_A_DATUM,
    CMD_BLE_STATE_TIME_STAMP_START,//Might need several due to data limitations
    CMD_BLE_STATE_TIME_STAMP_RECEIVE_YEAR,
    CMD_BLE_STATE_TIME_STAMP_RECEIVE_MONTH,
    CMD_BLE_STATE_TIME_STAMP_RECEIVE_DAY,
    CMD_BLE_STATE_TIME_STAMP_RECEIVE_HOUR,
    CMD_BLE_STATE_TIME_STAMP_RECEIVE_MINUTE,
    CMD_BLE_STATE_TIME_STAMP_RECEIVE_SECOND,
    CMD_BLE_STATE_GET_LOG,//Get the SD card log
    CMD_BLE_STATE_HELP,
    CMD_BLE_STATE_ERROR,
} CMD_BLE_STATE_VALUE;


uint32_t ble_cus_init(ble_cus_t * p_cus, const ble_cus_init_t * p_cus_init)
{
    //Init statemachine for reading the commands

    CMD_BLE_STATE_VALUE = CMD_BLE_STATE_START;//Move to start state
    CMD_STARTED = true;

    if (p_cus == NULL || p_cus_init == NULL)
    {
        return NRF_ERROR_NULL;
    }

    uint32_t   err_code;
    ble_uuid_t ble_uuid;

    // Initialize service structure
    //p_cus->evt_handler               = p_cus_init->evt_handler;
    p_cus->conn_handle               = BLE_CONN_HANDLE_INVALID;
    //p_cus->conn_handle               = BLE_CONN_HANDLE_INVALID;

    // Add Custom Service UUID
    ble_uuid128_t base_uuid = {CUSTOM_SERVICE_UUID_BASE};
    err_code =  sd_ble_uuid_vs_add(&base_uuid, &p_cus->uuid_type);
    VERIFY_SUCCESS(err_code);
    
    ble_uuid.type = p_cus->uuid_type;
    ble_uuid.uuid = CUSTOM_SERVICE_UUID;

    // Add the Custom Service
    err_code = sd_ble_gatts_service_add(BLE_GATTS_SRVC_TYPE_PRIMARY, &ble_uuid, &p_cus->service_handle);
    if (err_code != NRF_SUCCESS)
    {
        return err_code;
    }
    // Add Custom Value characteristic
    return custom_value_char_add(p_cus, p_cus_init);
}
uint32_t custom_value_char_add(ble_cus_t * p_cus, const ble_cus_init_t * p_cus_init)
{
    uint32_t            err_code;
    ble_gatts_char_md_t char_md;
    ble_gatts_attr_md_t cccd_md;
    ble_gatts_attr_t    attr_char_value;
    ble_uuid_t          ble_uuid;
    ble_gatts_attr_md_t attr_md;

    memset(&char_md, 0, sizeof(char_md));

    char_md.char_props.read   = 1;
    char_md.char_props.write  = 1;
    char_md.char_props.notify = 0; 
    char_md.p_char_user_desc  = NULL;
    char_md.p_char_pf         = NULL;
    char_md.p_user_desc_md    = NULL;
    char_md.p_cccd_md         = NULL; 
    char_md.p_sccd_md         = NULL;
		
    memset(&attr_md, 0, sizeof(attr_md));

    attr_md.read_perm  = p_cus_init->custom_value_char_attr_md.read_perm;
    attr_md.write_perm = p_cus_init->custom_value_char_attr_md.write_perm;
    attr_md.vloc       = BLE_GATTS_VLOC_STACK;
    attr_md.rd_auth    = 0;
    attr_md.wr_auth    = 0;
    attr_md.vlen       = 0;

    ble_uuid.type = p_cus->uuid_type;
    ble_uuid.uuid = CUSTOM_VALUE_CHAR_UUID;

    memset(&attr_char_value, 0, sizeof(attr_char_value));

    attr_char_value.p_uuid    = &ble_uuid;
    attr_char_value.p_attr_md = &attr_md;
    attr_char_value.init_len  = sizeof(uint32_t);//was Uint8_t
    attr_char_value.init_offs = 0;
    attr_char_value.max_len   = sizeof(uint32_t);

    err_code = sd_ble_gatts_characteristic_add(p_cus->service_handle, &char_md,
                                               &attr_char_value,
                                               &p_cus->custom_value_handles);
    if (err_code != NRF_SUCCESS)
    {
        return err_code;
    }

    return NRF_SUCCESS;
}

void ble_cus_on_ble_evt( ble_evt_t const * p_ble_evt, void * p_context)
{
   ble_cus_t * p_cus = (ble_cus_t *) p_context;

   if (p_cus == NULL || p_ble_evt == NULL)
   {
       return;
   }
   
   switch (p_ble_evt->header.evt_id)
   {
       case BLE_GAP_EVT_CONNECTED:
           on_connect(p_cus, p_ble_evt);
           break;

       case BLE_GAP_EVT_DISCONNECTED:
           on_disconnect(p_cus, p_ble_evt);
           break;
       case BLE_GATTS_EVT_WRITE:
           on_write(p_cus, p_ble_evt);
           break;
       default:
           // No implementation needed.
           break;
   }
}
void on_connect(ble_cus_t * p_cus, ble_evt_t const * p_ble_evt)
{
    p_cus->conn_handle = p_ble_evt->evt.gap_evt.conn_handle;

}
void on_disconnect(ble_cus_t * p_cus, ble_evt_t const * p_ble_evt)
{
    UNUSED_PARAMETER(p_ble_evt);
    p_cus->conn_handle = BLE_CONN_HANDLE_INVALID;
}
void on_write(ble_cus_t * p_cus, ble_evt_t const * p_ble_evt)
{
    ble_gatts_evt_write_t * p_evt_write = &p_ble_evt->evt.gatts_evt.params.write;
    
    uint32_t found_data = 0;
    
    // Check if the handle passed with the event matches the Custom Value Characteristic handle.
    if (p_evt_write->handle == p_cus->custom_value_handles.value_handle)
    {
        memcpy(&found_data, p_ble_evt->evt.gatts_evt.params.write.data, p_ble_evt->evt.gatts_evt.params.write.len);

        Process_Command(p_cus, p_ble_evt,found_data);
    }
}
uint32_t ble_cus_custom_value_update(ble_cus_t * p_cus, ble_evt_t const * p_ble_evt, uint8_t custom_value)
{
    NRF_LOG_INFO("In ble_cus_custom_value_update. \r\n"); 
    if (p_cus == NULL)
    {
        return NRF_ERROR_NULL;
    }

    uint32_t err_code = NRF_SUCCESS;
    ble_gatts_value_t gatts_value;

    // Initialize value struct.
    memset(&gatts_value, 0, sizeof(gatts_value));

    gatts_value.len     = sizeof(uint8_t);
    gatts_value.offset  = 0;
    gatts_value.p_value = &custom_value;

    // Update database.
    err_code = sd_ble_gatts_value_set(p_cus->conn_handle,
                                      p_cus->custom_value_handles.value_handle,
                                      &gatts_value);
    if (err_code != NRF_SUCCESS)
    {
        return err_code;
    }

    // Send value if connected and notifying.
    if ((p_cus->conn_handle != BLE_CONN_HANDLE_INVALID)) 
    {
        ble_gatts_hvx_params_t hvx_params;

        memset(&hvx_params, 0, sizeof(hvx_params));

        hvx_params.handle = p_cus->custom_value_handles.value_handle;
        hvx_params.type   = BLE_GATT_HVX_NOTIFICATION;
        hvx_params.offset = gatts_value.offset;
        hvx_params.p_len  = &gatts_value.len;
        hvx_params.p_data = gatts_value.p_value;

        err_code = sd_ble_gatts_hvx(p_cus->conn_handle, &hvx_params);
    }
    else
    {
        err_code = NRF_ERROR_INVALID_STATE;
    }


    return err_code;
}
void Process_Command(ble_cus_t * p_cus, ble_evt_t const * p_ble_evt, uint32_t command)
{
    if((command == CMD_BLE_START) && (CMD_STARTED == 0))
    {
        CMD_BLE_STATE_VALUE = CMD_BLE_STATE_START;//Move to start state
        CMD_STARTED = true; 
    }
    NRF_LOG_INFO("Command is: %d",command);
    if(Processing_Commands == false){
        switch (CMD_BLE_STATE_VALUE)
        {
          case CMD_BLE_STATE_START://Start command issued
               //See next command
               NRF_LOG_INFO("Start state");
               CMD_BLE_STATE_VALUE = CMD_BLE_STATE_SELECT_COMMAND;  
               break;//Removed break as to fall into other states
           case CMD_BLE_STATE_SELECT_COMMAND://Start command issued
               //See next command
               NRF_LOG_INFO("Command state");
               if(command == CMD_BLE_STOP)
               {
                  CMD_BLE_STATE_VALUE = CMD_BLE_STATE_STOP;//Move to stop state
                  NRF_LOG_INFO("Go to stop state");
               }
               else if(command == CMD_BLE_HELP)//HELP
               {
                  CMD_BLE_STATE_VALUE = CMD_BLE_STATE_HELP;//Move to help state
                  NRF_LOG_INFO("Go to help state");
               }
               else if(command == CMD_BLE_SD_LOG)//SD Logging
               {
                  CMD_BLE_STATE_VALUE = CMD_BLE_STATE_SD_LOGGING;//Move to SD logging state
                  NRF_LOG_INFO("Go to SD log state");
               }
               else if(command == CMD_BLE_UART_LOG)//UART LOGGING
               {
                  CMD_BLE_STATE_VALUE = CMD_BLE_STATE_UART_LOGGING;//Move to uart log state
                  NRF_LOG_INFO("Go to UART state");
               }
               else if(command == CMD_BLE_READ_DATAM)//Read a datam
               {
                  CMD_BLE_STATE_VALUE = CMD_BLE_STATE_READ_A_DATUM;//Move to help state
                  NRF_LOG_INFO("Go to Read datum state");
               }
               else if(command == CMD_BLE_TIME_STAMP_START)//Receive the timestamp
               {
                  CMD_BLE_STATE_VALUE = CMD_BLE_STATE_TIME_STAMP_START;//Go to reading the timestamp date
                  Processing_Commands = true;//Set to process the rest of the commands
                  NRF_LOG_INFO("Go to Timestamp state");
               }
               else if(command == CMD_BLE_GET_LOG)//Get the log
               {
                  CMD_BLE_STATE_VALUE = CMD_BLE_STATE_GET_LOG;//Get the log
                  NRF_LOG_INFO("Go to log state");
               }
               else
               {
                  CMD_BLE_STATE_VALUE = CMD_BLE_STATE_ERROR;//Move to error state unknown command
                  NRF_LOG_INFO("Go to error state");
               }
               if(Processing_Commands == false){
                  Process_Selected_state(p_cus, p_ble_evt, command);//Run the command
               }
               break;//Removed break as to fall into other states
           default:
               // No implementation needed.
               break;
         }
    }//End of case statements
    if(Processing_Commands == true){
        Process_Selected_state(p_cus, p_ble_evt, command);//Run the command
    }
}
void Process_Selected_state(ble_cus_t * p_cus, ble_evt_t const * p_ble_evt, uint32_t command)
{
switch (CMD_BLE_STATE_VALUE)
{
    ret_code_t err_code;
    case CMD_BLE_STATE_HELP:
        NRF_LOG_INFO("Help state");
        NRF_LOG_INFO("Help info is:");
        err_code = ble_cus_custom_value_update(p_cus, p_ble_evt,m_custom_value);
        APP_ERROR_CHECK(err_code);
        CMD_BLE_STATE_VALUE = CMD_BLE_STATE_SELECT_COMMAND;  
        break;
    case CMD_BLE_STATE_SD_LOGGING:
        NRF_LOG_INFO("SD card LOG state");
        CMD_BLE_STATE_VALUE = CMD_BLE_STATE_SELECT_COMMAND;  
        break;
    case CMD_BLE_STATE_UART_LOGGING:
        NRF_LOG_INFO("Uart Logging state");
        CMD_BLE_STATE_VALUE = CMD_BLE_STATE_SELECT_COMMAND;
        if(Print_log_enabled == 1)//Toggle the printing
        {
            Print_log_enabled = 0;
            NRF_LOG_INFO("Logging disabled");
        }
        else
        {
            Print_log_enabled = 1;
            NRF_LOG_INFO("Logging enabled");
        }
        break;
   case CMD_BLE_STATE_READ_A_DATUM:
        NRF_LOG_INFO("Reading datam state");
        CMD_BLE_STATE_VALUE = CMD_BLE_STATE_SELECT_COMMAND;
        SD_CARD_Read_Line();//Run the read command for the SD card reading
        break;
    case CMD_BLE_STATE_TIME_STAMP_START:
        NRF_LOG_INFO("Receiving Time stamp data");
        //CMD_BLE_STATE_VALUE = CMD_BLE_STATE_SELECT_COMMAND;
        CMD_BLE_STATE_VALUE = CMD_BLE_STATE_TIME_STAMP_RECEIVE_YEAR;
        //Need to read the time stamp data here
        break;
    case CMD_BLE_STATE_TIME_STAMP_RECEIVE_YEAR:
        NRF_LOG_INFO("Receving year");
        Time_Year = command;//Set the year
        NRF_LOG_INFO("Year data is: %d",Time_Year);
        CMD_BLE_STATE_VALUE = CMD_BLE_STATE_TIME_STAMP_RECEIVE_MONTH;
        break;
    case CMD_BLE_STATE_TIME_STAMP_RECEIVE_MONTH:
        Time_Month = command;//Set the month
        NRF_LOG_INFO("Receving month");
        CMD_BLE_STATE_VALUE = CMD_BLE_STATE_TIME_STAMP_RECEIVE_DAY;
        break;
    case CMD_BLE_STATE_TIME_STAMP_RECEIVE_DAY:
        Time_Day = command;//Set the day
        NRF_LOG_INFO("Receving day");
        CMD_BLE_STATE_VALUE = CMD_BLE_STATE_TIME_STAMP_RECEIVE_HOUR;
        break;
    case CMD_BLE_STATE_TIME_STAMP_RECEIVE_HOUR:
        Time_Hour = command;//Set the hour
        NRF_LOG_INFO("Receving hour");
        CMD_BLE_STATE_VALUE = CMD_BLE_STATE_TIME_STAMP_RECEIVE_MINUTE;
        break;
    case CMD_BLE_STATE_TIME_STAMP_RECEIVE_MINUTE:
        Time_Minute = command;//Set the minute
        NRF_LOG_INFO("Receving minute");
        CMD_BLE_STATE_VALUE = CMD_BLE_STATE_TIME_STAMP_RECEIVE_SECOND;
        break;
    case CMD_BLE_STATE_TIME_STAMP_RECEIVE_SECOND:
        Time_Second = command;//Set the second
        NRF_LOG_INFO("Receving second");
        CMD_BLE_STATE_VALUE = CMD_BLE_STATE_SELECT_COMMAND;//Finished
        Processing_Commands = false;//Finished processing the
        Convert_time(Time_Year,Time_Month,Time_Day,Time_Hour,Time_Minute,Time_Second);
        NRF_LOG_INFO("Time in unix is: %d ",Unix_Time);
        break;
    case CMD_BLE_STATE_GET_LOG:
        NRF_LOG_INFO("Sending SD card log");
        //Need to send the SD card log here]
        break;
    case CMD_BLE_STATE_STOP://Stop command issued
        NRF_LOG_INFO("Stop state");
        CMD_STARTED = false;//Ready for next command
        CMD_BLE_STATE_VALUE = CMD_BLE_STATE_START;  
        break;
    case CMD_BLE_STATE_ERROR://Stop command issued
        NRF_LOG_INFO("Error state");
        NRF_LOG_INFO("Unknown command:");
        CMD_STARTED = false;//Ready for next command
        CMD_BLE_STATE_VALUE = CMD_BLE_STATE_START;  
        break;
    default:
    // No implementation needed.
    break;
    }
}

[Sigurd]

As indicated in my second reply, you can get the BLE_ERROR_GATTS_INVALID_ATTR_TYPE if the handle you are using is pointing to a characteristic that don't support notifications (char_props.notify).

This seems to be the case here, since you have char_md.char_props.notify = 0; in your code(custom_value_char_add() function).