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Flea86 ("Tiny XT class machine") Review

mbbrutman

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Back in January I was lucky enough to get an early copy of the Flea86 single board computer. Here is the original thread where it was introduced:


After only seven months I have finally gotten around to writing a review of it. If you are curious about the Flea86 and want to know what one really is like to use, this should answer some of your questions ...


Valentin has been great in answering questions and discussing the design with me. I'm sure that if you have questions and post them here either I can answer them or Valentin will step in. (With the right answer!)


Mike
 

mbbrutman

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He's alive and well, and contemplating doing a larger run of machines ... I had him review my review for technical accuracy to make sure I didn't get anything too far wrong.
 

Trixter

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Neat machine and neat review. In fact, reading the review left me with some questions, like why not go all the way and emulate the SHR/SHL/ROR/ROL,immed instructions to go full 80186 -- would let some more games run. Also, I'm curious how accurate the emulation is (like, does the Flea86 emulating a 4.77MHz machine perform like one).
 

Chuck(G)

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I seem to recall that Valentin may have done some of the extended instructions.

He's not cycle-for-cycle correct, but things appear to run accurately in the gross sense. We fooled around with some of the old Pianoman music files, which really sound strange if the timing's off.

The last time we corresponded, I think he was bemoaning that he was running out of program memory in the 8052 MCU he was using. I wondered if he was going to move his design to a 32-bit MCU that didn't have all of the issues of an 8-bit one.
 

basman74

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Neat machine and neat review. In fact, reading the review left me with some questions, like why not go all the way and emulate the SHR/SHL/ROR/ROL,immed instructions to go full 80186 -- would let some more games run.
Well, in addition to the 8088/86 opcode set, Flea86 also supports PUSH/POP/SHR/SHL/ROR/ROL immediate as well as the PUSHA/POPA opcodes. Anything beyond that is not supported by the default Flea86 firmware. Interrogating the CPU flags register will yield an 8088 and also POP CS is supported.

Also, I'm curious how accurate the emulation is (like, does the Flea86 emulating a 4.77MHz machine perform like one).
Flea86's hardware emulation isn't cycle-exact as Chuck pointed out, though it is a pretty good approximation (many classic games targeting a 4.77MHz machine play surprisingly well - save for a few games that generate timer-interrupt-driven digitized speech through the PC speaker, resulting in a large 8253 processing overhead and emulation slowdown). For the curious, Appendix-A of the Flea86 User Manual provides a reasonable summary of the emulator status for comparison with real hardware.. :)


Regards, Valentin
 
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Maverick1978

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Very nice review, Mike... Valentin, the "final" pcb looks quite nice! I didn't realize that you had gone into production on these. Would love to see pricing, etc, when they become available again.
 

basman74

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Very nice review, Mike... Valentin, the "final" pcb looks quite nice! I didn't realize that you had gone into production on these. Would love to see pricing, etc, when they become available again.

Thanks! I did a small prototype (pre-production) run around the beginning of the year to iron out any major bugs in the Flea86 system. Managed to squash most of the critical bugs before Mike and several other testers received their flea systems, thankfully.. :)

Flea86 would've been available already, had a certain custom programming interface (used to burn the on-chip OTP ROM's of the Flea's host micro) NOT gone belly-up and all the problems/delays that caused. Currently waiting for an opportunity to do another run of system boards - will keep you posted!

Regards Valentin
 
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Mike Chambers

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Good review, Mike. I've got one the prototypes as well, mine is labeled "PRE-03" so I guess your "PRE-02" is mine's older brother. It's a really cool little system, with SDHC card reader on-board and everything. I've spent quite a few hours playing with mine, and I can only recall one software compatibility issue caused by a CPU emu bug. The Flea86 tripped on 16-bit executables compiled with Open Watcom C. They would hang the system immediately upon execution, which was pretty odd. Valentin and I were scratching our heads trying to figure out what could have been causing it. I had the exact same bug in Fake86, too. We figured it out pretty quickly though, and fixed both of the emus. I doubt you guys want to read the boring details, but it was related to how we were parsing/skipping over FPU opcodes.

In any event, yeah the Flea86 is an impressive piece of work. Valentin's a talented hardware designer and programmer. I'm surprised he was able to squeeze so much speed out of that weak 8-bit CPU, especially when you consider some of it had to be reserved for generating the video and audio signals. It seems to run a bit quicker than a real 4.77 MHz 8088. It feels like it's somewhere in the area of 7 or 8 MHz.
 

basman74

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It seems to run a bit quicker than a real 4.77 MHz 8088. It feels like it's somewhere in the area of 7 or 8 MHz.

That might be due to the fact that Flea86 starts up in 'Turbo mode' by default ;-) The option for a 4.77MHz system clock can be set either using the FLEASET.EXE utility or by running an executable file upon startup, containing little more than a few specific OUT opcodes.

Regards Valentin
 
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