[Coco] 6309 running in a Coco 1

[William Astle]

The advantage of the double clock applies also to 6809 native mode. If 
the double clock is being applied inside a 6309 conditional, the source 
code is broken. It should be applied or not regardless of the CPU mode. 
Presence or absence of a 6309 makes no difference to whether the machine 
itself can handle running in double speed mode. It should be noted that 
the "regular" (address dependent) speed up (65495/FFD7) is useless under 
Nitros9 because it only speeds up ROM accesses and has no effect on RAM 
accesses.

I would expect a noticeable speedup even without specially optimized 
code from the switch to native mode simply because many instructions 
execute faster by 1 or 2 cycles. How much of a speedup that gives 
depends on the mix of instructions. Code designed to use the extra 
registers and some of the more useful extra instructions can benefit 
even further (block moves, for instance, can yield a substantial speedup).

On 14-01-02 10:43 PM, Bill Pierce wrote:
>
> Thanks William, I'm not that proficient on the 6309 modes.
> So the Nitros9 code "could" be assembled to 6309 native mode for Coco 1&2. Would there be much advantage to this without the double clock? I have no clue as to how much speed would be gained in native mode without the clock speedup.
> In this case, all that would be needed is for the makefiles to be altered to include the 6309 conditionals in the level 1 builds and disks to be made. Can this be done without setting the clock speed up in the conditionals?
>
> Since I don't have a 6309 on any of my Cocos, I never messed with it much other than using the 6309 Nitros9 L2 builds for the Vcc emulator.
> My Coco 3 has the Disto 1-meg upgrade which has a DAT board soldered directly to the 6809 so upgrading it to a 6309 would be a NIGHTMARE. Mark at Cloud9 told me he wouldn't touch it :-) I would love to have a 6309 in there. I remember back when one of the vendors in Rainbow was doing the 6309 speedup kit, a friend of mine had his Coco 3 set up with the kit. We put our Cocos side by side, mine running hacked/patched (for speed) OS-9 on a 6809, his running the original NitrOS-9 on a 6309. The difference was amazing at the time. One of the best examples we found was the "landscape" 3D graphics demo for OS-9. His Coco would be a screen or so ahead of mine, leaving it behind LOL
> The funnt thing is the "landscape" demo was written in 6809 code aso all his speed was coming from the Nitros9 graphics driver with 6309 code. I could only imagine what it could have done had the landscape demo been written in 6309 asm!
>
> Bill Pierce
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>
>
> -----Original Message-----
> From: William Astle <lost at l-w.ca>
> To: coco <coco at maltedmedia.com>
> Sent: Fri, Jan 3, 2014 12:18 am
> Subject: Re: [Coco] 6309 running in a Coco 1
>
>
> This is actually incorrect. 6309 native mode has nothing to do with
> clock speed. All it does is change the cycle counts for many
> instructions. It does not change the clock speed. In fact, the CPU
> itself has exactly zero control of the clock speed and the switch to
> native mode is a flag in a CPU register. You can perfectly happily run a
> coco 1 or 2 in 6309 native mode.
>
> On 14-01-02 09:35 PM, Bill Pierce wrote:
>> The problems I see with this is that you couldn't run in 6309 native mode on
> Coco 1&2. (Dragons too I think). Since the 6309 native mode runs at double clock
> speed, the Coco 1&2 would lose video just as it does when using the poke65495,0
> & poke65497,0 in Basic. It's the very reason the double clock wasn't used by
> software on the 6809 back in the 80s. The VDG chip can not take the speedup.
> Possibly the SAM as well (???). On the Coco 1, the bitbanger port cannot use
> this mode as well. That's why there's no "Turbo mode" DW4 drivers for Coco 1.
> The Coco 1 had a flawed serial output and maxes at 38,400.
>
>
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