Calls and callbacks

The library handles function calls asynchronously. The system returns results in the form of callbacks. All calls to the library are non-blocking.

Calls will return a result to say whether or not they were accepted. You provide a callback function in the call. If a call is accepted, you will receive a response in the user-provided callback function. You must write functions to handle the response.

Because the library processes asynchronously, and callbacks are required to get additional info from the attendant, a number of callback routines must be specified. The library returns these callbacks to the above calls whenever additional input is required.

These callbacks are asynchronous responses to a synchronous call:

1. Library initialization callback
2. Register POS callback
3. Register PED callback
4. Create tender callback
5. Cancel or Refund callback
6. Show Screen callback
7. TxStoreReport callback
8. Library exit callback

These callbacks are related to transactions, and will require actions to be performed:

1. Receipt callback
2. Signature callback
3. Additional data callback 

These callbacks are related to transactions, and will require no actions to be performed:

1. Progress event callback
2. Dynamic Currency Conversion callback
3. Final result callback
4. PED State callback