Monday, July 21, 2014

WinUSB communication with STM32 round 2 (Part 2: Client)

Previous client application is linked against WinUSB and SetupAPI libraries. This was a bit of a bother with WDK and project settings. They are loaded dynamically in new client test application. Two thin wrappers load the libraries and provide needed function calls with same prototypes as original library functions. SetupAPI is needed at low level for enumeration and when creating connection. WinUSB is further wrapped in an object representing USB device. And later wrapped in Comm interface explained in another post.
USB device object uses two USB pipes to transfer data which takes two USB endpoints in bulk mode at device side. One for sending data to device and other to receive it. Messaging control is done through USB control endpoint. Transfer sequence is optimized from previous implementation. Sending a complete application packet consists of sending a control message with the 32 bits length of the packet and then writing the packet data to bulk pipe. Receiving a packet is done with reading the return size through the control endpoint util nonzero length is returned and then reading the packet data from second endpoint. Application packet is meant to be a complete data set needed for single operation on device and can be larger than endpoint buffer.
Comm wrapper mentioned earlier is an implementation of the layer interface as specified by Comm library. Comm library core utilizes this interface to make transferring of data easier to application. WinUSB Comm layer is written to be the last layer in stack, also referred to as "physical" layer as is the closest to the physical medium on the master (client) side - Windows PC.
Application is written to test the connection and speed. Device is expected to return same data as sent by application. Speed is calculated from time it takes to send and receive back the packet.

Application uses Comm library methods to transfer the data. It is just that the Comm library object is initialized with comm layer using USB. It could instead be some other communication type, e.g. serial port or TCP/IP.

[Source files]

This is the second post in this series (of total 2 posts). See 1.


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