Preston Hamlin (pwh11@my.fsu.edu)
This project is based on the "short" device driver for parallel port hardware
from the "Linux Device Drivers" (LDD3) book by Jonathan Corbet, Alessandro
Rubini and Greg Kroah-Hartman. This driver uses pins 2-9 of the parallel
hardware port to connect to a custom device as described below.
The code within these files is largely written by myself, and any code that is
of a differing nature is stated as such in the files. My code borrows
significantly from the LDD3 book as well as the "short" kernel module which
also is used to interact with parallel port devices. Note that I used the
word interact rather than communicate. There is little to no functionality
to perform handshakes with advanced hardware as a prelude to further\
communication. Since not all of the pins are utilized, there is also a
limit to bandwidth and functionality.
The device to be used is a simple wiring of pins to a led display. Each pin,
when powered, illuminates a segment of the display. Bytes are written to
the device, each bit having one pin.
My code functions by maintaining state via static global variables. These are
used to determine whether or not to continue writing to the device or not.
If the device were to be removed or the module unloaded, it would be rather
problematic if the module were to continue scheduling parts of itself with
the kernel.
Each second, the next number in a sequence is displayed until the maximum term
is reached. When this happens the counter will either halt, displaying the
final term, or wrap around to 0 and begin again. Since a number composed of
more than one digit can be sent to the device, the digits must be displayed
in sequence, but in a way such that they are still legible. There is a set
minimum length of time which a digit will be displayed, so long numbers may
take more than a second to display.
Since it can be obscure when one number ends and another begins, a feature to
impliment might be the flashing of the horizontal segment between numbers
to signify the border between digit sequences.
=== Tasks ===
Blank until first write.
Blank on module removal.
Display # of wall-clock seconds since write().
Skips some numbers as necessary.
Write time as unsigned int.
Check write size.
Fail with EINVAL if bad length.
Set modulus to that value.
Set counter to 0.
Read time as unsigned int.
Check read size.
Fail with EINVAL if bad length.
Returns the time on the clock.
Init and Cleanup
Cleanup stops any further scheduling.
Compile-time flags.
Wrap/stop.
Digit display time.
Blank display time.
Middle segment flash.
IOCTL
PAUSE
WRAP
DISPLAY
Tests
Read and write.
Change parameters.
Multiple access.