USB Flash Memory

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People can save and move data from one computer to another using USB flash disks. If you have a USB port and want to access USB flash disks, then you need a USB driver.


For the EHCI controller

EHCI is probably the most supported USB controller in hobby operating systems.

Initialize the controller

After finding the controller, you have to initialize it. Implementations may vary from OS to OS, but the basic line is the same.

  • Enable Bus Master and Memory Space
  • Save Base Address
  • Save Operational Base Address
  • Save Extended Capabilities Pointer
  • Check if Extended Capabilities Pointer < 40; if true, skip this step
    • Check if BIOS owns the controller; if true, get ownership
  • Stop and reset the controller (but not start)
  • Setup Queue Head
  • Start the controller

Find devices

  • Scan USB ports for connected devices; if false, go to next port
  • Check if low speed; if true, go to next port (mass-storage devices are hi-speed)
  • Reset and enable the port which contains the device.

Prepare devices

  • Get device-configuration-interface-endpoint descriptors.
    • Check if the device is mass-storage class
    • Check if the device responds to SCSI commands
    • Check if the protocol is Bulk-Only
    • If all above true, proceed
  • Assign unique USB address and use it from now
  • Assign device configuration (usually got from configuration descriptor)
  • Get and use endpoints from endpoint descriptor
  • Send Inquiry Command
  • Send Test Unit Ready Command
  • Send Read Capacity Command


Only after those steps, request read and write commands.

See Also

External Links

  • TatOS website — a hobby operating system the main feature of which is a driver for USB flash drives.
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