README  tatOS usb    Feb 2016

This usb driver code was developed from scratch and has evolved over the years.
It is not perfect. No usb analyser has been used to check it.
The flash drive init sequence usually passes but sometimes fails.
Then I just reinit the controller and go thru the flash sequence again.
It will almost always pass the 2nd time.

Not all flash drives behave the same. Some will go thru the init sequence quickly
the first time without fail, others may stall or slow down at some point.

There are times when a write10 may fail so I  go back and reset the 
controller and go thru the flash init sequence again and try the write10 again
and it fails again. Then I just reboot. Sorry thats life.



POLLING
**********
The usb driver code does not use interrupts, but uses polling.  See run.s
We wait/poll for the usb controller to mark the tranfer descriptor as inactive
or failed, before continuing code execution. I have only dabbled into getting
the usb controller to issue a hardware interrupt on successful completion of a TD
but have not been successful. It involves finding the registers that control
legacy support and PIRQD routing.  On bootup the bios will enable legacy support 
and enable usb keyboard hardware interrupts but route thru irq1. I did not want to 
fall back on legacy support.  Then there are registers to enable the usb controller to generate interrupts and also an PCI->ISA bridge register to route that interrupt 
to whatever irq you choose, and then the usb TD must be generated to issued an 
interrupt on completion of the TD. A bit of work must be done here.


HUB
****
As of 2015 there is now code to init an "integrated root hub".  This hub is built into
my Acer laptop and it allows a usb 1.0 (low speed device) like a mouse or keyboard
to communicate with an ehci hi speed controller. The use of uhci companion controllers
is apparently obsolete.  I have a Lenova desktop with 2 ehci controllers
that also has an integrated root hub (also called "rate matching hub").


KEYBOARD
*********
As of 2016 we now have usb keyboard code.  This keyboard code is identical to the 
usb mouse except for the buffer pointers and device address and endpoint numbers. 
In fact you can use the mouse init sequence on the keyboard and it will work.  
Both the keyboard and mouse are "low speed" HID (human interface device).
So in the interest of time I just copied the mouse code files to keyboard, 
changed the address where the descriptors are stored and used unique values for 
device address and proper endpoint.  Also new queue heads are required in the 
frame list in order to conduct seperate interrupt transfers for each device.
Some day I may spend time compacting the code and eliminating duplication but
its not a priority right now.


Thats all folks.
Enjoy your usb transactions.

Tom Timmermann
Janesville WI USA