How to use USB_RELAY_DEVICE DLL
===============================

Version 2.0

Changes to the original DLL:
----------------------------
 - The type used for handles changed from int to intptr_t, for 64-bit compatibility.
   This should be binary compatible with existing 32-bit clients. 
 - Added helper functions for use from managed languages and scripts; see below.  


Windows, Visual C++ applications
---------------------------------

Include file name: usb_relay_device.h
Library file name: usb_relay_device.lib

Put the following lines in your source file:

   `#include <usb_relay_device.h>`

   `#pragma comment(lib, "usb_relay_device.lib")`

The file usb_relay_device.dll must be installed with your application.
Use either 32-bit or 64-bit DLL, matching your application.
The DLL may require VC++ redistributable runtime library.
   
Using the API:
--------------   

 * `usb_relay_init()`
 Call this before calling other functions

 * `usb_relay_device_enumerate`
 Enumerates all Relay devices plugged into the PC.
 Returns list of usb_relay_device_info structures.
 Caller should free this list by passing it to usb_relay_device_free_enumerate().
 
 * `usb_relay_device_open`
 Opens one Relay board device by its usb_relay_device_info structure,
 obtained from usb_relay_device_enumerate().

 * `usb_relay_device_open_with_serial_number`
 Opens one Relay board device by its serial number string.
 These strings can be obtained from usb_relay_device_enumerate().
  
 * `usb_relay_device_open_one_relay_channel`
  Turns ON one channel of a Relay board.
  Parameters: 
     - device handle, obtained from usb_relay_device_open()
     - Index: integer from 1 to the maximal number of channels on a board.
  
 * `usb_relay_device_open_all_relay_channel`
  Turns ON all channels on a board.
  
 * `usb_relay_device_close_one_relay_channel`
  Turns OFF one channel of a Relay board.
  Parameters: 
     - device handle, obtained from `usb_relay_device_open()`
     - Index: integer from 1 to the maximal number of channels on a board.

 * `usb_relay_device_close_all_relay_channel`
  Turns OFF all channels on a board.
 
 * `usb_relay_device_get_status`
  Get status of all channels on a board as a bit mask.
  The least significant bit in returned value corresponds to channel 1.
  Bit value 1 means the corresponding relay is switched ON, value 0 means the relay is OFF.
  
 * `usb_relay_device_close`
  Closes the Relay device handle opened by `usb_relay_device_open()` or
   `usb_relay_device_open_with_serial_number()`
 
 * `usb_relay_exit`
  Finalizes the library

 
  
Helper functions for managed callers and scripts
------------------------------------------------

These functions help to use this lib in managed languages.  
Native C or C++ callers do not need to use these.  
The ptr_usb_relay_device_info parameter is pointer to `struct usb_relay_device_info`, converted to a pointer-sized integer.
Type `int` means the "C" integer (which usually is 32-bit), `ptr` is a pointer-sized integer.  

 * `ptr_usb_relay_device_info usb_relay_device_next_dev(ptr_usb_relay_device_info)`  
    Returns pointer to the next element of device list obtained from `usb_relay_device_enumerate`
	
 *  `int usb_relay_device_get_num_relays(ptr_usb_relay_device_info)`  
    Returns number of relay channels on the device. Values <= 0 are not valid and mean error.
  
 *  `ptr usb_relay_device_get_id_string(ptr_usb_relay_device_info)`  
    Returns the "serial number" string of the device, as pointer to constant C string (one-byte characters, null terminated).

 *  `int USBRL_API usb_relay_device_lib_version()`   
   Returns the version of the library.
   The lower 16 bits are the library version. Higher bits: undefined, ignore.
	
 * `int usb_relay_device_get_status_bitmap(intptr_t hHandle)`  
   Returns the states of all channels on a relay device as a bit mask.
   This is same as `usb_relay_device_get_status` but without dereferencing pointers.
   Negative returned values indicate error. Else, bits 0-7 of the value are states of each channel.

  
Error handling
---------------
If error occurred, the API functions that return error code return -1;
functions that return handles or pointers return NULL.
Application is responsible to check the returned value.
  
Notes
-------
 * The library does not detect hot plug/unplug of USB devices.
 * The library is not thread-safe. Client application must ensure that 
  only one thread calls the library.

  
Managed .NET applications (C#, VB.NET)
---------------------------------------
TBD

Python (CPython)
-------------------
TBD

GCC or MinGW applications
--------------------------
TBD