[Coco] Another speed question

[Bob Devries]

Gene, et al,

I have the 6850 spec/data sheets here in my Motorola manual. If anyone needs 
it I can scan it to PDF easily.

The 6850 was used in the Atari ST series for the rs232 and Midi ports.

--
Regards, Bob Devries, Dalby, Queensland, Australia

Isaiah 50:4 The sovereign Lord has given me
the capacity to be his spokesman,
so that I know how to help the weary.

website: http://www.home.gil.com.au/~bdevasl
my blog: http://bdevries.invigorated.org/

----- Original Message ----- 
From: "Gene Heskett" <gene.heskett at verizon.net>
To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
Sent: Friday, September 07, 2007 1:15 PM
Subject: Re: [Coco] Another speed question


> On Thursday 06 September 2007, Becker, Gary wrote:
>>I am using a UART compatible with the 6850, not the bit bang port. The
>>6850 has interrupt generation capabilities, but I have never tested my
>>implementation. My driver does not enable the interrupt capability and I
>>intentionally disable CPU interrupts.
>
> I just did a google search for details on the 6850 uart, but came up 
> pretty
> thin in the first 3 pages of hits.  No real data sheets fell out.
>
> I know that the 6551 used in the dc connect modem pack and the rs-232 pack 
> is
> a fairly intelligent chip, and that the IRQ routines are already written 
> for
> this one.
>
> Unless you can duplicate its code for the 6850, I'd be rather tempted to 
> just
> switch chips for one that is completely compatible with os9/nitros9 at any
> conceiveable baud rate up to 115k.  The cpu loading is miniscule for the 
> 6551
> at any reasonable baud rate.
>
> See the Rainbow's article on "The forgotten Chip" which describes how to
> install a 6551 so that it actually works through the bit-banger port, I 
> used
> one of those to talk to a GVG 300-3A/B television production switcher for
> about 13 years at WDTV.  I was replacing a $20,000 GVG EDisk option with a
> coco2 running os9 level one with a couple of floppy drives, doing the job
> with english filenames, and 4x faster than the EDisk.
>
>>-----Original Message-----
>>From: coco-bounces at maltedmedia.com [mailto:coco-bounces at maltedmedia.com]
>>On Behalf Of Gene Heskett
>>Sent: Thursday, September 06, 2007 9:45 AM
>>To: CoCoList for Color Computer Enthusiasts
>>Subject: Re: [Coco] Another speed question
>>
>>On Thursday 06 September 2007, Becker, Gary wrote:
>>>In a different thread, it was mentioned that the bit bang serial port
>>>and the hires mouse adapter takes too much CPU time. I understand why.
>>>Both devices use CPU timing loops and the interrupts have to be turned
>>>off. This discussion caused me to think about the way that I am doing
>>>the Serial Virtual Drive for the CoCo3FPGA under NitrOS-9. At the
>>>present time, I turn off interrupts and poll the serial port until I
>>
>>get
>>
>>>the 256 byte sector. This takes approximately 25 mS. Since task
>>>switching happens every 16+ mS, I am guaranteed to miss at lease one
>>>interrupt. After the sector is received, I re-enable the interrupts. I
>>>do this because I am afraid that I cannot service interrupts from the
>>>serial port fast enough to keep up at 115200 bps. But I have never
>>>tried.
>>>
>>>It would take a major rewrite of the driver to make it interrupt
>>
>>driven.
>>
>>>Is it worth the effort? Would it be better to lower the serial port /
>>>drive speed to keep interrupts enabled?
>>
>>I don't believe this is possible due to where would one get the IRQ
>>question?
>>If edge triggered, how many bit spaces have elapsed since the last one?
>>
>>One possibility that may or may not have been explored is that there may
>>be a
>>timer function in the gime, which could be programmed to fire an IRQ
>>everytime a bit time has elapsed, minus of course the exec time of the
>>service routine itself.  Or on a repeat basis but how would one go about
>>
>>achieving the initial bit synch unless the start bit coming in was a
>>separate
>>IRQ service routine to set that up, and then disable it till the stop
>>bit
>>comes in.
>>
>>I haven't looked at that recently, so I have NDI if its granularity
>>could be
>>bent into a std rs232 timing stream.
>>
>>>Gary
>>>
>>>
>>>
>>>
>>>--
>>>Coco mailing list
>>>Coco at maltedmedia.com
>>>http://five.pairlist.net/mailman/listinfo/coco
>
>
>
> -- 
> Cheers, Gene
> "There are four boxes to be used in defense of liberty:
> soap, ballot, jury, and ammo. Please use in that order."
> -Ed Howdershelt (Author)
> My life is a patio of fun!
>
> --
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