SGI SN-921 dial box working! (was Re: Seeking software for SGI/Sun dial box) - test-drb@ccmp.vtda.org

10 Apr 2018

On Sun, Apr 8, 2018 at 5:01 PM, Ethan Dicks <ethan.dicks at gmail.com> wrote:
...
  On Sun, Mar 25, 2018 at 3:48 PM, Ethan Dicks
<ethan.dicks at gmail.com> wrote:
  SN-921
   https://upload.wikimedia.org/wikipedia/commons/7/74/Sgi_dialbox_sn-921_fron…

  >>
https://github.com/hanshuebner/sgi-dialbox-usb/blob/master/dialbox.py 
 I'm going to test this code out when I have a dialbox in hand. 
 I have now tried this and am not having success.  I have a traffic
 light on the serial cable and I know I'm getting chars out of the host
 and that I don't have TxD and RxD swapped.  I'm not seeing any
 responses from the dial box and the python script does all the
 initialization and just sits there.  Frobbing the knobs produces no
 blinks on the traffic light and no text from the script. 
OK.  I got the script working and two things were impediments:

1) One of the SN-921 pinouts running around on the 'net is incorrect,
as I posted.  The *correct* place for the ground is DE-9 pin 7.  I was
apparently getting enough of a parasitic ground to get chars *from*
the SN-921 but not *into* the SN-921.

As it turns out, it appears the SN-921 as set up for the SGI is mute
except for a single status success byte 0x20.  If you send it an INIT
command (also 0x20), it will respond with its success after a fraction
of a second, which leads to another problem...

2) The python script dialbox.py slams the init code and a command to
set the dials to auto-report all at once, before the SN-921 has a
chance to initialize.  So to fix that, I added a few extra lines to
send the 0x20 INIT command, pause, check for a 0x20 response (INIT
GOOD) _then_ send the AUTO command (0x50 0x00 0xFF), which sets all 8
dials (one bit per dial) to send back a 3-byte packet when twisted.

With the custom serial cable fixed and the init sequence fixed in the
Python script, I'm now getting the right data stream when I twist any
of the knobs.

I did get a copy of dialbox.c from
http://www.geocities.ws/joekrahn/dialbox.tgz  Jim Stephens tracked
down that there was a massive GeoCities scan done in 2009 and the file
I was looking for happened to be scooped up then.  There are a number
of dial box and button box command sets in that code which reveals
some of the more complex behavior possible.

Here's a slice of the command byte definitions...

#define DIAL_INITIALIZE                 0x20

#define DIAL_SET_AUTO_DIALS             0x50
#define DIAL_SET_AUTO_DELTA_DIALS       0x51
#define DIAL_SET_FILTER            0x53

#define DIAL_SET_TEXT                   0x61
#define DIAL_SET_BUTTONS_MOM_TYPE       0x71
#define DIAL_SET_AUTO_MOM_BUTTONS       0x73
#define DIAL_SET_LEDS                   0x75

#define DIAL_SET_ALL_LEDS        0x4b

It should be possible to write up a protocol definition from studying
the code.  I do not have one of these button boxes so I can't validate
its behavior.

-ethan