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--- blog:fall2015:tmosgrov:journal [2015/11/18 17:49] – [11/16/2015] tmosgrov
+++ blog:fall2015:tmosgrov:journal [2015/12/02 21:02] (current) – [12/02/2015] tmosgrov
@@ Line 503: / Line 503: @@
 Generally after a usb device is plugged in it is already being accessed by the host.
+[[http://eleccelerator.com/tutorial-about-usb-hid-report-descriptors/|Report Descriptors]]
+"A USB HID report descriptor is one of the descriptors that a USB host can request from a USB device. HID devices send data to the host using reports, and the descriptor tells the host how to interpret the data."
+/usr/share/misc/usb_hid_usages Shows ideal report descriptor formats for various usb devices.
+====12/02/2015====
+Back to USB. I've been looking in all the wrong places. The library I should have been focusing on was libusb which references all of the other libraries I have occasionally stared far too long at. Those of which were probably being referenced as a lower level layer by libusb.h.
+Regarding libusb,
+When interfacing with usb devices you have two choices Synchronous, and Asynchronous. Synchronous offers a less involved method for interfacing with a USB device to make a transfer. Offering a "one function call" solution to make a transfer, but those calls may "sleep" inside libusb_bulk_transfer() until a transfer has completed. This could be a pain if a transfer process is taking longer than expected to complete. While Asynchronous offers a more controlled route with the ability to cancel a transfer, but is more complicated to use.
+note: Asynchronous offers simultaneous I/O operations or threading. Which libusb supports with its thread-control.
+**USB Transfer Types**
+  * Control Transfers
+  * Interrupt Transfers
+  * Isochronous Transfers
+  * Bulk Transfers
+**Control Transfers**- Command or status operations.
+**Interrupt Transfers**- Initiated by the device to request some action from the host.
+**Isochronous Transfers**- Transfers which are used to carry data the delivery of which is crucial.
+**Bulk Transfers**- Transfers which are used to carry data the delivery of which is not crucial.
+"All transfers take the form as packets, which contain certain control information and error checking fields."
+**The typical libusb procedure**
+  - Get device list
+  - Clear device list with libusb_free_device_list)
+  - Claim usb interface with libusb_claim_interface
+  - Do the desired I/O operations
+  - Release the device by using libusb_release_interface
+  - Close the device libusb_close
+  - Exit session libusb_exit

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