[Coco] DriveWire for TC-9/SWTPC/M68MM17

[Joel Ewy]

On 12/29/2013 07:09 PM, Steve wrote:
> As Aaron already pointed out, the use of the Bit-banger on the CoCo is 
> far from the best solution for transferring data from one computer to 
> another.  (Be it drivewire or not.)  The use of a UART, USB or 
> Bluetooth hardware solution is preferred over the CPU doing all that 
> work.
>
> The main reason drivewire uses Bit-banging is cost and convenience.  
> Not all CoCo setups have the Deluxe RS-232 pak on them.  Also, a good 
> programmer (like Aaron) can fine tune the Big-Banging code to transfer 
> faster than the Deluxe RS-232 pak.

Steve, this was my understanding -- that a UART like the 6850 or 6551 
couldn't keep up with the Bit-banger if used in the wayDriveWire does.  
And my purpose is not to transfer data to and from these computers with 
zmodem or some such, but actually to hook these other OS-9 computers up 
to a DriveWire 4 server.  For me it would be much simpler to build a 
little adapter to use the existing DriveWire code off the rack than to 
try to re-jigger somebody's fine tuning, or re-implement a DriveWire 
client over a UART.

The way it looks at the moment, the TC-9 may be able to run the stock 
CoCo DW client, assuming FHL didn't do something untoward with all the 
PIA pins, which is a distinct possibility.  The SWTPC and Motorola MM17 
have 6821s in the free and clear, but are clocked at 1 or 2 MHz.  So to 
get them to work, they would have to be "clock chipped" or the DW 
routines will need to be tweaked for a different clock rate.

JCE

>
> There are a number USB and Bluetooth modules that will easily 
> interface to these "old time" computers.  Their main advantage besides 
> transfer speed is their large FIFO buffers that keeps buffer overrun 
> errors to a minimum.  I used a number of hard wired and wireless 
> modules in custom projects for the Haunt industry with great success.
>
> Steve
>
>
> On 12/29/2013 2:47 PM, Joel Ewy wrote:
>> Just to confirm my understanding:  The CoCo's Bitbanger uses pins 
>> from PIA IC4.  DriveWire for the Dragon uses the same client driver 
>> with the addition of a little extra hardware to invert and possibly 
>> level-translate the same pins from its 6821 parallel port. Correct?  
>> So with a similar adapter one should be able to use one of the TC-9 
>> Tomcat's PIAs for DriveWire, and the same should be true of a 6821 
>> board on an SWTPC, GIMIX, Motorola Micromodule 17, S-100 6809, or 
>> SBC, assuming you are using the driver appropriate to your CPU type 
>> and clock speed, and you have a descriptor pointing at the right 
>> address.
>>
>> Actually, as I think about it, the clock speed might be a problem. 
>> The DW code is very, very tight and relies on instruction timings 
>> that are only going to be valid for the exact clock speed of the 
>> CoCo.  So if you have an SWTPC running at 2 MHz it won't be able to 
>> run an unmodified DriveWire client written to work at 1.78MHz, will 
>> it?  Since the TC-9 uses the GIME it is probably running at CoCo 3 
>> speed, though I think I remember FHL claiming some kind of speed-up.  
>> How hard would it be to modify the DW client code to run at 2 MHz or 
>> 1 MHz?  Or would it be worth it to replace the crystals and drop 
>> 10-20% of the CPU clock to get DriveWire?  Hmm.
>>
>> JCE
>>
>
>
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