[Coco] Webpage Update - Hires Mouse

[Arthur Flexser]

Seems like it might be possible to minimize the jitter that you'd get with
interrupts not disabled.  Maybe test the current calculated value against
the previous one and disregard it if it is too far off from what's
expected, perhaps substituting an interpolation based on the previous
couple of values.  I expect there are probably published algorithms
available for minimizing mouse jitter.

Art


On Thu, Oct 29, 2015 at 4:14 AM, Nick Marentes <nickma at optusnet.com.au>
wrote:

> The new mouse driver is certainly cycle-sensitive as Art stated.
>
> It samples the area between two DAC positions. The change from one DAC
> position to the next happens very fast but we manage to obtain 5 samples
> during that transition period and another 5 in the opposite. The minimum
> timing we obtain with a stock 6809 is 4 cycles from the moment we set the
> second DAC point. Oversampling is timed to the clock cycle and the routine
> needs full access during that time to get the most accurate reads possible.
>
> So, interrupts do need to be turned off. It may work under Nitros9 without
> but you may get "mouse jiggle" due to the interrupts. That's what
> interrupts do, they interrupt the current flow of processing.
>
> So turn off interrupt first and you should be fine.
>
> Oh, and the current code is designed for 6809 timings. Putting a 6309 into
> the 6309 timings mode may add post processing errors unless the sample
> weights are re-adjusted.
>
> The code presented is also not relocatable so it would need to be modified
> to suit Nitros9's requirements. This is not impossible, it's just that
> RS-DOS apps have fixed loading points normally.
>
> So, it's quite possible but as Art said, it will need a bit more work to
> make it Nitros-9 friendly.
>
> Note also, that this routine, with all the post processing happening, is
> faster than the hardware hires mouse driver method. It too ideally wants
> the IRQ's off to obtains the most accurate results to avoid "mouse jitter".
>
> Nick
>
> On 29/10/2015 2:27 PM, Arthur Flexser wrote:
>
>> Bill, I think you might be underestimating the difficulty of adapting the
>> new joystick routine to NOS9.  As I see it, the problem is not so much
>> getting it to run under NOS9, which you seem to be focusing on.  The
>> problem is doing so without affecting the accuracy of the joystick
>> reading.  After reading Nick's description at
>> http://www.members.optusnet.com.au/nickma/ProjectArchive/hires.html
>> I have the impression that the coding is quite cycle-sensitive.  As I
>> understand it, you need to get a reading exactly 4 cycles after you set a
>> new DAC voltage value. To accomplish this, at the least, you'd need to
>> disable interrupt servicing during joystick reading, which I hope doesn't
>> mess up too much stuff going on in other processes, particularly with
>> respect to communications.  (Note the ORCC #$50 as the first instruction
>> of
>> the source Nick has posted.)  Also, rewriting the code to make it
>> position-independent may play havoc with critical cycle counts.
>>
>> I'm certainly no authority on NOS9, but it strikes me that there may be
>> significant problems involved that you haven't considered.
>>
>> Art
>>
>
>
>
>
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