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DataLogging

Detailed Description

Enables logging data asynchronously to a mobile app.

In Pebble OS, data logging is a data storage and transfer subsystem that allows watchapps to save data on non-volatile storage devices when the phone is not available to process it. The API provides your watchapp with a mechanism for short-term data buffering for asynchronous data transmission to a mobile app.

Using this API, your Pebble watchapp can create an arbitrary number of logs, but you’re limited in the amount of storage space you can use. Note that approximately 640K is available for data logging, which is shared among all watchapps that use it. This value is subject to change in the future. When the data spool is full, an app will start overwriting its own data. An app cannot overwrite another apps's data. However, the other app might have 0 bytes for data logging.

Your app can log data to a session, either creating, adding or deleting data to that session. The data is then sent to the associated phone application at the earliest convenience. If a phone is available, the data is sent directly to the phone. Otherwise, it is saved to the watch storage until the watch is connected to a phone.

For example:

To create a data logging session for 4-byte unsigned integers with a tag of 0x1234, you would do this:

DataLoggingSessionRef logging_session = data_logging_create(0x1234, DATA_LOGGING_UINT, 4, false);
// Fake creating some data and logging it to the session.
uint32_t data[] = { 1, 2, 3, 4 };
data_logging_log(logging_session, &data, 4);
// Fake creating more data and logging that as well.
uint32_t data2[] = { 1, 2 };
data_logging_log(logging_session, &data, 2);
// When we don't need to log anything else, we can close off the session.
data_logging_finish(logging_session);

For code samples, refer to Examples/data-logging-demo.

Function Documentation

DataLoggingSessionRef data_logging_create ( uint32_t  tag,
DataLoggingItemType  item_type,
uint16_t  item_length,
bool  resume 
)

Create a new data logging session.

Parameters
tagA tag associated with the logging session.
item_typeThe type of data stored in this logging session
item_lengthThe size of a single data item in bytes
resumeTrue if we want to look for a logging session of the same tag and resume logging to it. If this is false and a session with the specified tag exists, that session will be closed and a new session will be opened.
Returns
An opaque reference to the data logging session
void data_logging_finish ( DataLoggingSessionRef  logging_session)

Delete a data logging_session. Logging data is kept until it has successfully been transferred over to the phone, but no data may be added to the session after this function is called.

Parameters
logging_sessiona reference to the data logging session previously allocated using data_logging_create
DataLoggingResult data_logging_log ( DataLoggingSessionRef  logging_session,
const void *  data,
uint32_t  num_items 
)

Add data to the data logging session. If a phone is available, the data is sent directly to the phone. Otherwise, it is saved to the watch storage until the watch is connected to a phone.

Parameters
logging_sessiona reference to the data logging session you want to add the data to
dataa pointer to the data buffer that contains multiple items
num_itemsthe number of items to log. This means data must be at least (num_items * item_length) long in bytes
Returns
DATA_LOGGING_SUCCESS on success DATA_LOGGING_NOT_FOUND if the logging session is invalid DATA_LOGGING_CLOSED if the sesion is not active DATA_LOGGING_BUSY if the sesion is not available for writing DATA_LOGGING_INVALID_PARAMS if num_items is 0 or data is NULL

Enumeration Type Documentation

The different types of session data that Pebble supports. This type describes the type of a singular item in the data session. Every item in a given session is the same type and size.

Enumerator
DATA_LOGGING_BYTE_ARRAY 

Array of bytes. Remember that this is the type of a single item in the logging session, so using this type means you'll be logging multiple byte arrays (each a fixed length described by item_length) for the duration of the session.

DATA_LOGGING_UINT 

Unsigned integer. This may be a 1, 2, or 4 byte integer depending on the item_length parameter.

DATA_LOGGING_INT 

Signed integer. This may be a 1, 2, or 4 byte integer depending on the item_length parameter.

Enumerator
DATA_LOGGING_BUSY 

Someone else is writing to this logging session.

DATA_LOGGING_FULL 

No more space to save data.

DATA_LOGGING_NOT_FOUND 

The logging session does not exist.

DATA_LOGGING_CLOSED 

The logging session was made inactive.

DATA_LOGGING_INVALID_PARAMS 

An invalid parameter was passed to one of the functions.