[Coco] Re: Coco Digest, Vol 11, Issue 104

[farna at att.net]

-------------- Original message from coco-request at maltedmedia.com: -------------- 

> Message: 3 
> Date: Mon, 27 Sep 2004 11:46:55 -0700 
> From: "John R. Hogerhuis" 
> Subject: [Coco] DriveWire boot 
> I need to find an alternative way to boot DriveWire; I have an old 
> floppy drive, but I'm having trouble reading the drivewire floppy disk 
> sent. It's probably an alignment issue, which I don't know how to fix. 
> Anyway, I'm hoping to remove the floppy drive from the equation 
> altogether. 
> 
> I'd like to put the OS-9 boot program on cassette. I guess what I need 
> is the boot track off the drivewire diskette. 
> 
> If I could bootstrap off cassette, then I could disconnect from the 
> cassette as soon as the bootloader is transferred. 


I hate to be the bearer of bad news, but I don't think this will work. IIRC OS-9 has no provisions to use the cassette port at all. I'm sure someone has written a utility to utilize the motor on/off commands, but that's about it. 


> Message: 9 
> Date: Mon, 27 Sep 2004 16:25:58 -0400 (EDT) 
> From: James Dessart 
> Subject: RE: [Coco] CoCo Progression... 
> On Mon, 27 Sep 2004, David Gacke wrote: 
> 
> > The new CPU would be backward compatible with the old CPU. Also, it's 
> > much easier to implement some of the new features in the list of items 
> > you mentioned if they are attached to a new cpu. 
> > 
> > A possible idea would be to leave the addresses from 0-ffff as is for 
> > legacy support, including the bank switching, gime register maps, etc. 
> > And build the new features in above that address. 
> > 
> > Also, it's easy to emulate a CPU, it's much harder to emulate the 
> > idiosyncrasies (timing, etc) of a graphics chip. 
> 
> I think that's essentially what they did with that C64 processor 
> replacement. They created a new CPU that emulates the 6502, added some 
> features, used a high clock for the processor, and there you go, easy to 
> add onto a C64, using the same peripherals and software. 
> 
> Any modern CPU architecture could be used to emulate the 6809, in fact, 
> you could probably get decent performance out of a cheap PIC or AVR, and 
> have modern compiler support for new development. Somewhat like the 6309 
> software out there. So you'd still have the GIME, but you could write 
> software that uses the native instruction set of the procesor used. 
> 
> I can definitely see this working well, whereas on the other hand, I'm not 
> sure what making a new GIME would get us, except headaches for the 
> developer. The 6809 is well documented, the GIME is not. It's much easier 
> to work with well documented hardware. 

While the GIME isn't well documented, it is the key to all CoCo (3) graphics. Apparently the company that made the chips for Tandy were told to do so as cheaply as possible (okay, that just makes sense because it was, after all, a cheap computer!). The GIME can't be run any faster than it does or it will cease functioning. I think someone got it to run reliably at around 2.5 MHz, but that's about all. It's a 2 MHz rated part and the manufacturer pushed on that! A heat sink might get it up to 3 MHz, but that's not fast enough for any fourth generation machine. It needs to run at 8-10 MHz at least, but I'd push for around 20 MHz speed for any 4th gen machine now. 8-10 would be plenty fast for an experimental/hobby machine, in my opinion though. A single sided board about half the size of the CoCo 3 with adequate I/O built on would be fantastic! I know there are those (including myself) who would like to see any such creature with DECB compatibility, but I'd settle for NitrOS9 compatibility only. There was a program out that would run at least some DECB games from OS-9 without leaving OS-9. Something like that should be easy on a machine that runs 5-10 times faster than an original CoCo or CoCo 3 with a couple GB of memory to work with. You'd just need a disk copy of the DECB ROMs like you do with the emulators now. 


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