Voltage problem?

I'm still working on my Retrochallenge entry. There are only a few more days in the month, and I feel like I'm pretty close to the goal. However, it could be that a good ol' hardware issue has me stuck.

I've reverse-engineered some of the code from the "vfloppy" program, and figured out how the PC serial port is used to talk to the PX-8. It's very straightforward, as I thought, based on the specs - 8 bits, no parity, 38400 baud, no flow control, just raw I/O. No magic at all. And that's exactly the way the serial code for the Propeller works, too, by default. So, why do I not have reliable communication?

Based on the trouble I had making the vfloppy program work with one computer and not another, it occurred to me that serial port voltage/current might be an issue. I checked the Epson PX-8 tech specs, and it looks like the serial and RS232 ports on the PX-8 want +/- 8V. Standard RS232 voltage is +/- 12V, and that's what the MAX3232 chip (used on the Propeller development board for serial communications) puts out. So, I'm wondering if there's a sufficient voltage mismatch as to be causing communication issues? Seems unlikely, but I'm kind of at a loss to understand why this is being so difficult to get going.

Anyhow, I'll keep working - perhaps I can put some resistors in line, and see if that improves the situation.

The first speed bump

When trying to accomplish something with technology, it seems like there are always these strange "gotchas". I've encountered the first on my road to a PX-8 virtual drive prototype...

As I set out to produce the PX-8 virtual floppy drive, one resource that I'm hoping to use for reference is the open source, Linux-based "vfloppy" program (see previous post). Turns out, vfloppy works great on my old Dell laptop, but not on my newer one (Dell D630). Both are running Ubuntu 10.04 LTS, both have the same serial UART, and they are configured identically. However, with the D630, I get serial communication errors, and with the older Dell Inspiron, I don't. Ugh.

Since I've got the source code, I went poking around to see how the serial port is initialized and opened in the vfloppy program (epspdv3.c). It's pretty straightforward stuff using the standard libraries. Should be about as hardware non-specific as you can get.

Thinking it might be my specific D630, I tested another that I had handy. Same issue. So the problem is not with faulty hardware, but with some specific hardware/software issue.

I know problems come up when trying to accomplish something - it's part of the challenge of a project. But this is my least favorite kind of problem, because it is, at best, only a tangent to the real problem I'm trying to solve.

I might just be stuck using my older laptop for the project, unless some magic happens...

PX-8 virtual drive: Next stop - Linux and vfloppy!

The vfloppy disk simulator is software that acts like a disk drive for the Epson HX-20 and PX-8 systems. It is written in C, for Linux. It's regularly updated, and now supports the D88 virtual disk file format used by the PX-4/PX-8 emulators produced by Toshiya Takeda.

All the software in play here is GPL/open-source, which is awesome. Having an open, working, updated implementation of the disk drive simulation will be very helpful in my efforts to produce a Propeller-based virtual drive.

This is the most current and best solution I'm aware of for emulating the Epson PF-10 floppy drive on a modern system, so I'm off to install Linux on a spare machine. Rather than use a virtual machine and have the potential hazards of uneven serial port support, I'm putting this on real hardware. I'm going with Ubuntu 10.04 on a Dell Inspiron laptop. Will be nice to take the new Ubuntu for a test drive anyhow!

Retrochallenge 2010 begins!

The Epson PX-8s are charging their NiCads - warming up for their role in my entry for this year's Retrochallenge event. May the games begin!

PX-8 Virtual Drive, take 2

The Epson PX-8 is a circa 1984 laptop computer, running the CP/M operating system (ROM based). Last I checked, you can still purchase new PX-8 systems from Star Technology. However, the PF-10 3.5" portable disk drive for the PX-8 is a very rare beast - the ones I've seen on eBay I've never been able to afford.

Communications between the PX-8 and PF-10 are over an RS-232 compatible connection at 38400 baud. The protocol is documented, and there are a couple of software packages - one for Linux, and one for DOS - that emulate the drive. I would like to extend the work that's already been done in this field, and create a portable, battery-operated virtual disk drive for the PX-8.

I'm hoping to be able to use a Propeller microcontroller chip as the "brains" of the virtual drive. The Propeller is cool - 8 parallel cores or "cogs" typically running at 80 MHz nominal clock speed. There are hardware/software solutions for interfacing with external storage, including SD cards.

Like last year, I've entered the Retrochallenge contest with the goal of producing a first pass at a virtual drive prototype. Unlike last year, this year I hope to achieve the goal!

More postings as I go. Look for details on this blog, with the tag label "retrochallenge".