Setting a Real Time Clock with ZMODEM

I have had a little extra time lately since I don't have to commute for a while, so I pulled the CMS boards out of their storage boxes. One of the the things I really wanted to test out on real hardware is a routine I developed for setting the real time clock on the CMS board. Since my MC6809 ZMODEM routines are working pretty well, I decided to try out sending a command over ZMODEM, instead of a file.

Basically, if the receiver allows it, a ZMODEM sender can send a command for the receiver to execute. With the right flags, the standard lrz program will execute the commands in the system shell. Unfortunately, the receiver does not respond with the results of the command - it is not part of the protocol, since it is a receiver. But, the protocol allows you issue a command to start a ZMODEM send process to send the results, stored in a file, back to yourself! So, if I have the CMS 9619 send a ZMODEM command like this: date "+%y%m%d %H%M%S">/tmp/date.txt; lsz -y /tmp/date.txt

My terminal computer will get the date and time in the CMS 9619's expected format and save it to a file. Then, as ordered, it starts the lsz ZMODEM sender program, and sends the file contents back to the CMS 9619! The sender and receiver temporarily switch places to transfer the date string. Then the debug ROM's standard time setting routine is run to load the time into the RTC. It seems weird but it is the result of a very flexible protocol.

Now, ZMODEM does include an extension to get the system date, but it is sent as seconds since the Unix epoch. Converting that to an actual date and time without the proper libraries in 6809 assembly was beyond my skill set. Instead, the terminal (my MacBook Air) can do all of the work.

With gnu screen running on the terminal computer it is all pretty much automatic:

The screenshot of the session with the CMS9619 shows:

1. set the incorrect time
2. verify it is wrong
3. run the ZMODEM command routine, which instructs on how to start lrz
4. screen automatically starts lrz on my terminal
5. everything completes
6. checking the time with the "T" command, shows the correct date and time for the RTC!

Now to get the board setup to run NitrOS-9!

NitrOS9 on (an emulated) CMS 9619

I have been working on some ideas to expand my CMS 9619 SBC. I thought an SD card interface would be a nice option, but I didn't want to use any modern microcontrollers or FPGAs. I had a circuit pretty much worked out, but then thought a Compact Flash card would work better for 8 bit transfers.

While working on a circuit to interface with the MC6821, I realized that I already have a nice RS232 connection to the computer, why not use it? So, I wrote a 6809 assembly tool for the CMS 9619 debugger (debug19) to download blocks of data using the zmodem protocol.

This was working so well, that I figured I could use it to boot load NitrOS-9 on the board. Since I am moving soon, my computers are all packed away, but I couldn't wait to try it. I made some changes to sbc09, a simple 6809 emulator, to emulate the CMS 9619. Here is a video of the boot process to NitrOS9 all the way to the shell:

And it works! I need to finish a real zmodem driver to get it running other commands on the disk image though. Once I move, I can test it out on a real computer.