This is a simple driver which displays a signon message then accepts calls to write to the LEDs. Normal writes cause the text to scroll across the display.
There is also an ioctl call supported. Function 0 re-displays the signon message and function 1 displays the string pointed to by the third argument, padding to and truncating at 8 characters as necessary.
More than one device is supported in this driver and the default configuration sets up four. Each device may only be opened by one process at a time. When more than one device is opened at the same time the ones with the lower minor number are blocked until they become the highest. This allows something like a clock, for example, to continuously display the time but still allow other processes to take over the display on a temporary basis. When the second process is finished with the device the clock display will resume.
This driver has been tested on an Everex STEP/25 running ESIX 5.4.0.4 beta. Information about the usage of the 8042 UPI has been derived from the Everex STEP 386 Hardware Service and Maintenance Guide, part number KIT 00076-00 (about a hundred bucks from your Authorized Everex dealer).