[Coco] CoCo <--> Raspberry Pi

Gene Heskett gheskett at shentel.net
Tue Mar 10 05:09:43 EDT 2020

On Tuesday 10 March 2020 00:57:50 James Ross wrote:

> Of interest as well was the CoCo <--> Raspberry Pi project discussed
> on the latest CoCoTalk – I caught a good 30 minutes of that
> conversation on the day.  I went back and listened to that whole
> section, it starts around the 3 hr mark ...)  Quite interesting, kudos
> to the dude that is experimenting w/ that.
> I wonder how fast you can feed data to the CoCo through the keyboard
> input, if bypassing the ROM and talking directly to the port in
> assembler?
> I imagine the Raspberry Pi (possibly only the newer ones 3, 4?) are
> fast enough to R/W directly to cartridge slot at full double speed
> 1.79MHz? ...
> - jr

Having experience at running a bigger old Sheldon 11x54" lathe I have 
converted to LCNC, with both a rpi3 and now an rpi4, I can testify that 
either can send a 4 byte packet, at 40 megabits/second and receive the 
responses from the interface card at 25 megabits per second, and is not 
breaking a sweat doing it thru a an SPI bus constructed of 3 wires from 
its gpio header.  The rpi3 has its tongue hanging out a bit but gets the 
job done, while the rpi4 is only boosted to an 800 megahertz clock, 
loafing on the job so to speak.

For anyone interested, get the linux preempt-rt kernel to be installed 
over the top of a raspbian 10.3 install, and the ready built debs to 
install LinuxCNC on the rpi4.

To find it on my web page, click on the link in my sig, add lathe-stf to 
the address bar, find linuxcnc4rpi4 in that directory listing, click on 
it and its all there includeing screenshots of it running and the config 
files that are doing it. Unforch the interface card and its buffers 
total about $200 from mesa electronics. More than the 2Gig pi4. But it 
works well and I have no intention of converting it to some other 

The lathes cnc conversion has removed the lathes compound feed since LCNC 
can do that far more precisely, (and it was smashed by a fallover) the 
taper kit has been removed for the same reason, no gears on the left 
face of the headstock, synchronization for cutting or boreing threads in 
any tpi OR tpmm is all done in the software, much faster than you can do 
it by hand or with the gears taken off & stored in a drawer.

The are no hand cranks on it as the whole apron has been removed and 
replaced with a front panel carrying a pair of jog dials should you want 
to do it yourself.  Or you can drive it one move at a time from the 
command line. Linuxcnc is even compensating for the bed wear of a 75 yo 
machine as it was built right after WW-II.

This springs project is to make a tool holder for a tap so that I can do 
rigid tapping, where you bore the hole, change the boring tool for a 
tap, and drive the tap into the hole at exactly the taps pitch, stop and 
reverse to draw the tap back out of the hole. But the tap can't be 
allowed to slip in the tool holder which is why the special toolholder.

Whats not to like if you are into that sort of thing?

Cheers, Gene Heskett
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law respectable.
 - Louis D. Brandeis
Genes Web page <http://geneslinuxbox.net:6309/gene>

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