On 25/10/2016 11:39, Dennis Lee Bieber wrote:
On Tue, 25 Oct 2016 11:02:31 +0100, BartC <b...@freeuk.com> declaimed the
following:
This gives you the ability to do (2) above. From that, you could do (1)
(echoing) and go on to build full line-orientated input. But you had
complete control.
So, why has it all become so difficult?
Because you now have an interrupt driven operating system with buffered
line handling between you and the hardware. The OS is handling things like
back-space/delete, <cr><lf> (from a single keypress -- for those systems
that use both for line ending), previous line recall/history.
Your polling loop on a status register basically meant nothing else was
happening on that computer until you retrieved a character
Only if you were specifically waiting for a key press. For the
requirement in the other thread (see link in OP), it just needed to know
if a key had been pressed; that would be very quick (I can't remember if
that status bit latched or not.)
Anyway the next step would have been to wire up the status bit to an
interrupt line.
and passed it on
to whatever program had requested it. Something doable on a
single-user/single-task system, but totally at odds with any system running
a few dozen separate processes.
I don't agree. Each single process shouldn't need to be aware of any of
the others. In the same way that the raw_input() example doesn't need to
take account of the other half-dozen Python programs all waiting on
raw_input() at the same time (which are all waiting for the same keyboard).
Hardware peripherals are now the domain of the OS, and mere users are
supposed to request the OS for data... That means OS specific methods for
bypassing the convenience mode of "cooked" input.
Fine, then let the OS provide the appropriate means if the user program
is not allowed to directly access the hardware. getch() and kbhit() are
crude but they will do for simple programs. But they are not part of the
OS. Implementing the equivalent via calls to Win32 is horrendous (and to
Linux not much better).
(BTW the computer I was using in 1976 had 160 simultaneous users. And
each had their own keyboard. Now usually there is just one keyboard...)
--
bartc
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