On Thu, Jan 3, 2013 at 4:20 AM, Jim Lemon <j...@bitwrit.com.au> wrote:
> On 01/03/2013 12:57 PM, dmccunney wrote:
>> On Wed, Jan 2, 2013 at 7:57 PM, Jim Lemon<j...@bitwrit.com.au>  wrote:
>>> If there was a Linux kernel in which the user could turn off everything that
>>> isn't in DOS, that would be a way out.
>> If you could turn off everything that *isn't* in DOS, you might have
>> fun running the Linux kernel.  You run DOS in an emulator on top of
>> Linux because you can't *get* DOS to run native on that hardware.
>> Drivers are needed that don't exist.
>> What you probably want is a flavor of Linux modified for use in an
>> RTOS, where a user process can preempt the kernel itself.
> Exactly. I intend to try out RTLinux at some point.

"Real time" simply means "guaranteed to respond to an external event
within a specified period".  What time period is required?

>> But on modern hardware, "other time-critical programs that will carve
>> out slices of CPU time" are likely a "Who cares?" issue.  Commonly
>> used hardware is orders of magnitude faster than the machines DOS was
>> made to run on, and there are cases like games where you might
>> specifically *want* to steal CPU slices, because otherwise your game
>> runs *too* fast and is unplayable. .
> I have had to do this once, when writing an assembly code driver for a
> digital rotation encoder. The read cycle had to be slowed down by a
> specified number of NOPs to allow the register to load. The problem is
> that when a program is monitoring response devices such as the mouse and
> keyboard and presenting an animated display to the user, even a
> millisecond lost to some other program is a disaster. As I can often see
> the system "blink" on modern PCs running Windows and even Linux, I'm
> reasonably certain that I can't trust them to be accurately recording
> reaction times. One of my colleagues thought that she had solved the
> problem by buying an expensive test battery until I showed her the
> "uncertainty" factor that came with every response recorded.

How accurately do you *need* to be recording reaction times?

For that use case, I'm not sure I'd try to run DOS on top of Linux,
even with a Linux version modified for RTOS usage.

The best option might be custom monitoring software running directory
on the RTOS, without DOS in the loop.

> Jim

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