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--- blog:fall2015:tmosgrov:journal [2015/11/16 16:29] – [11/09/2015] tmosgrov
+++ blog:fall2015:tmosgrov:journal [2015/12/02 21:02] (current) – [12/02/2015] tmosgrov
@@ Line 469: / Line 469: @@
 [[http://linux.die.net/lkmpg/x892.html|Talking to Device Files]]
+[[http://www.usbmadesimple.co.uk/|USB Made Simple]]
+====11/18/2015====
+USB/Bluetooth Notes:
+MAX devices 127
+USB devices uses a 7bit address
+"All communications on the bus are intiated by the host"
+There is no communication usb-device to usb-device.
+"A device cannot initiate data transfering, but must wait to be asked to transfer data by
+the host." The only exception being a 'suspend' that results in a remote wakeup.
+USB On-The-Go, An interesting extension on the USB spec.
+Cables specially designed to only connect host-to-device IE. not host-to-host, or
+device-to-device.
+Wire shielded cable two of which are a twisted pair (D+, D-). The fourth wire (VBUS)
+provides 5V supply of power.
+Additional Resources
+[[https://forums.freebsd.org/threads/usbhid-accessing-multiple-joysticks-in-one-report.53155/|USBHID Sample Source]]
+[[http://www.gsp.com/cgi-bin/man.cgi?topic=hid_get_report_desc#3|More USBHID Documentation]]
+Using libusbhid  & libfcntl.
+Ran into libfcntl while reading somones source that reads input from a joystick.
+libfcntl or (file control) provides a means to accessing a file that is already open.
+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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