Tech notice on ATMEGA8515 @ 20mhz

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Tech notice on ATMEGA8515 @ 20mhz

Postby vbriel » Aug Thu 12, 2010 8:17 pm

Seems overclocking the ATMEGA8515 works but some chips have strange side effects. I've decided to drop any remaining kits down to 16mhz for now and work on a replacement CPU adapter board.

If you kit suffers from not loading BASIC and running correctly, or other issues email me and I'll see if it fits in the description of the issues I've run into. If it does, you can send in the CPU for reprogramming and I'll send with it a 16mhz crystal to swap out on the board.

If you system works fine, I'd leave it go, this only will apply to people who can't get their board to function correctly. Email me at vince@brielcomputers.com and I can help work out issues.

Next month I'll work out a daughter board with a new CPU (If it is compatible) and it is native 20mhz so it can handle it with 0 issues! Sorry guys, sometimes these things don't pop up until a few units roll out. The only advantage to the new CPU upgrade board will be the stable 20mhz speed, so if your Altair micro is working good, then your CPU is stable at the 20mhz speed and you won't need the board.

Feel free to ask me any questions about this.

Vince
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Re: Tech notice on ATMEGA8515 @ 20mhz

Postby vbriel » Aug Thu 12, 2010 10:19 pm

Might not get the 20mhz CPU chip I wanted, it has 3 less IO pins and that would be a real pain. The shortage of 8515's has caused me to look into using an ATmega162 40 pin is a drop in replacement but the code has slight changes. This will really make things difficult when doing firmware updates. I just hope the 8515's come in soon.

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Re: Tech notice on ATMEGA8515 @ 20mhz

Postby galaga » Mar Thu 17, 2011 4:21 am

ok i did some math

i ran that prog and it did it in 5:00mins (wow you save 59sec!!!! :wink: )
so i did some more cal's and i worked out the atlair8080u is about 1.34MHz at 16MHz AVR8515
so 1.55MHz at 18.46MHz
.. 1.675MHz at 20MHz
therefore 24MHz would be needed to get it up to full speed 2.01, a major over-clock...

i was think about going to 18.46MHz but for 0.2MHz will it matter..

Ok, updates are going to start becoming regular. I probably should start a new forum soon since this project is going to be completed before too long.

I have 8K BASIC loaded and working great. I even have some early speed test results. Keep in mind, I haven't even started digging into speedups but I have a few tricks up my sleeve.

Test program:

10 FOR A=1 TO 100
20 FOR B=1 TO 1000:NEXT B
30 PRINT A
40 NEXT A

On Rich Cini's Altair32 tested at 2.04Mhz, this test completes in 3:35. On my system, it takes 5:59, so it is a little slow. These easiest way to speed things up is to increase the crystal from 16 to 20Mhz which I'll do next week. That alone is a 20% increase. I know there is a lot of slop in my code, so I'll be getting that cleaned up which will get it faster too.

The PockeTerm portion of the Altair is running at 9600, later on, I'll bump that up but for right now, it is fine for development. I may add a feature to allow you to use an external serial device instead of the built in terminal but that requires an extra IC to be added.

I should be able to achieve at least 80% speed. My goal is actual speed.

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Re: Tech notice on ATMEGA8515 @ 20mhz

Postby vbriel » Mar Thu 17, 2011 10:04 am

The question is if the Altair32 is running at estimated speed or actual calculated speed to emulate the 8080. You can try a faster crystal and see what you get but I found at least 25% failure rate on the machine. However, there are still some 20mhz machines out there.

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Re: Tech notice on ATMEGA8515 @ 20mhz

Postby risc » Apr Sat 09, 2011 2:14 am

On Rich Cini's Altair32 tested at 2.04Mhz, this test completes in 3:35.

I ran this test when I first got my Altair 8800 Micro, running Terminal 4.14 and 5.0 CPU firmware (not sure if this was a beta/pre-release, but SN 113 turned up with this installed) and the speed was around 4 minutes. Just ran it again with Terminal 5.0/CPU 5.0 offical and it came in at 3m17.8s. Amazing! :)
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Re: Tech notice on ATMEGA8515 @ 20mhz

Postby hal2710 » May Thu 19, 2011 10:55 am

risc wrote:
On Rich Cini's Altair32 tested at 2.04Mhz, this test completes in 3:35.

I ran this test when I first got my Altair 8800 Micro, running Terminal 4.14 and 5.0 CPU firmware (not sure if this was a beta/pre-release, but SN 113 turned up with this installed) and the speed was around 4 minutes. Just ran it again with Terminal 5.0/CPU 5.0 offical and it came in at 3m17.8s. Amazing! :)


Hi, Just wondering what speed crystal your using 16Mhz or 20 Mhz ? I just did this test and mine took 4min 12.2 secs.

I had installed Terminal 5.0 and CPU 5.0 and have downgraded the crystal to 16Mhz (From Vince) I'm SN 47 BTW


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Re: Tech notice on ATMEGA8515 @ 20mhz

Postby mikedoug » Apr Wed 10, 2013 11:34 am

Out of curiosity, I ran the BASIC benchmark listed in this thread on an 8800b running 8K BASIC ver 4.0. As a reference point, the test runs in 2:49 on real hardware.

I have found tests where the Altair32 emulator very closely matches the speed of real hardware, other tests where it differs substantially.
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