Exploring Introduction to service structure

[destiny98]

I am new to BLE and I am exploring Introduction to service. However I am stuck with Step 1 and Step 2. Is Step 1: static ble_os_t   m_our_service; (to declare a service) and step 2: our_service_init(ble_os_t*m_our_service); (the error says expected expression before ble_os_t). What is the way to define and initialise a service?

[Karl Ylvisaker]

Hello,

I am new to BLE and I am exploring Introduction to service.

Welcome! 

However I am stuck with Step 1 and Step 2. Is Step 1: static ble_os_t   m_our_service; (to declare a service) and step 2: our_service_init(ble_os_t*m_our_service); (the error says expected expression before ble_os_t).

How familiar are you with C and embedded programming?
In short, we need to declare that a new service exists - and then we need to fill in the empty service with the contents and functionality it will provide, by initializing it.
A more in-depth explanation of the concepts declaration, definition and initialization can be read here.

What is the way to define and initialise a service?

Have you retrieved the tutorials example code from the github?

Step 1 of the tutorial calls for declaration of a service structure.
If you check out the our_service.h file, you will see the code exempt:

/**
 * @brief This structure contains various status information for our service. 
 * It only holds one entry now, but will be populated with more items as we go.
 * The name is based on the naming convention used in Nordic's SDKs. 
 * 'ble’ indicates that it is a Bluetooth Low Energy relevant structure and 
 * ‘os’ is short for Our Service). 
 */
typedef struct
{
    uint16_t    service_handle;     /**< Handle of Our Service (as provided by the BLE stack). */
}ble_os_t;

Relevant examples of other, similar, declarations can be seen in main.c, for example:

static uint16_t m_conn_handle = BLE_CONN_HANDLE_INVALID;                        /**< Handle of the current connection. */

2: our_service_init(ble_os_t*m_our_service); (the error says expected expression before ble_os_t).

Here, you are supposed to pass the function the service structure you declared earlier.

Looking into the our_service.h file again, we see the following exempt:

/**@brief Function for initializing our new service.
 *
 * @param[in]   p_our_service       Pointer to Our Service structure.
 */
void our_service_init(ble_os_t * p_our_service);

Which means that the our_service_init function takes a pointer to a ble_os_t struct as its argument.
You must therefore provide this when you call the function, and it is done by using the referencing operator &, i.e passing the argument &m_our_service.
You should read more about referencing and pointers in this stackoverflow discussion, as it is crucial when working with C and embedded programming.

Please let me know if anything should still be unclear!

Best regards,
Karl

[destiny98]

Hi Karl, I tried the below code on SDK 16.0. I have referred to the replies from the Intro to services and followed some of the edits to the code to update it in SDK16.0. However I got the following error. What do they mean?

[Karl Ylvisaker]

Hello again,

Sorry for my late reply.

The ' conflicting types for "" ' error is commonly caused by providing the wrong type of argument to a function or structure.
You could read more about this error here and here.
I highly recommend using Stackoverflow to troubleshoot and learn more about the intrinsic of C programming.

Best regards,
Karl

[destiny98]

Hi Karl,

For Step 1 I have changed to : 

static uint16_t  m_our_service;

and Step 2: void our_service_init(ble_os_t * m_our_service);

And it is able to compile. However it does not advertise successfully. I tried to refer to the forum here about the changing the RAM_START/RAM_SIZE  for it to advertise it still does not work. What could I have done wrong?