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Flavioweb
Registered: Nov 2011
Posts: 447 |
1541 Quartz speed on real device.
With the help of Ready. we measured the quartz frequency of a 1541 directly on the motherboard, with the drive running, to make a precise test by evaluating the values in a condition of real operation.
This is the quartz mounted on the drive we have tested:
The test lasted about 2h and 30 mins, during which the electronics were covered to simulate the presence of the top of the chassis.
The maximum temperature reached by the quartz was about 45c if covered and about 39 if uncovered.
For the whole duration of the test a frequency value oscillating between 16.000 and 16.0001 mhz was detected. No values higher or lower than these.
In the quartz tech specs we found a maximum drift of +/- 50ppm, which means:
50 * 16 = 800 = 16.000.800 / 15.999.200hz in the worst case.
During our test, instead, we found, in the worst case, a drift of 100hz, therefore 1/8 of the theoretical one found in specs, ie 50/8 = 6.25ppm.
Making a few calculations just to relate ppm to rpm, we have:
6.25 / 5 = 1.25 (ppm / (1mhz / hz per revolution)) = drift per revolution
1.25 / 200,000 = 0.00000625
300 * 0.00000625 = 0.001875 rpm calculation error due to the quartz drift in the worst case.
We do not know exactly, during the whole period of normal operation of the drive, what is the precise value of ppm of deviation, but we know with certainty that it is a number between 16,000,000 and 16,000,100 hertz, so 100/16 = 6.25ppm in the worst case. |
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ready.
Registered: Feb 2003
Posts: 441 |
I used Rigol DS1054Z oscilloscope to measure the frequency. I relayed on the hardware frequency counter feature to measure the 1541 crystal frequency. Accuracy for this measurement should be less than 10ppm according to the tests I found here: http://nerdralph.blogspot.com/2015/07/rigol-ds1054z-frequency-c.. |
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chatGPZ
Registered: Dec 2001
Posts: 11108 |
I updated the readme with the info posted here, please check :) https://sourceforge.net/p/vice-emu/code/HEAD/tree/testprogs/dri.. (at the bottom of the file) |
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Flavioweb
Registered: Nov 2011
Posts: 447 |
Nice ! =) |
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Zibri
Account closed
Registered: May 2020
Posts: 304 |
Nice digression.
As I said before (without even doing all calculations and tests) the quartz drift is totally irrelevant to the results of 1541 Speed Test :D
And that's why I chose to accurately measure up to a cent of RPM.
I also checked the rpm page on sourceforge and noticed your rpm3.asm "inspired by 1541 speed test".
You even copied the (totally arbitrary) value I use for the byte I write. Why don't you do the right thing and take all the drive code from 1541 speed test and just call it from the test app?
If you like I can provide the drive code as stand-alone on github in the format you prefer. |
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Zibri
Account closed
Registered: May 2020
Posts: 304 |
Quoting ready.I used Rigol DS1054Z oscilloscope to measure the frequency. I relayed on the hardware frequency counter feature to measure the 1541 crystal frequency. Accuracy for this measurement should be less than 10ppm according to the tests I found here: http://nerdralph.blogspot.com/2015/07/rigol-ds1054z-frequency-c..
Very well done. |
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chatGPZ
Registered: Dec 2001
Posts: 11108 |
Quote:Why don't you do the right thing and take all the drive code from 1541 speed test and just call it from the test app?
It *is* equivalent code. |
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ChristopherJam
Registered: Aug 2004
Posts: 1378 |
This is fascinating. I wonder if the c64 crystal is as accurate? |
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Zibri
Account closed
Registered: May 2020
Posts: 304 |
Quoting ChristopherJamThis is fascinating. I wonder if the c64 crystal is as accurate?
Hmmm... we could measure it using the crystal in the drive, but I think it's just the same crystal.
Maybe I am wrong. |
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ChristopherJam
Registered: Aug 2004
Posts: 1378 |
Nah, crystal in a PAL c64 is nominally 17.734475MHz, which is divided by 18 to give a CPU clock of around 985kHz.
But yes, you could measure it against a drive crystal, which is exactly what RPM Test 1.0 does :) |
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Zibri
Account closed
Registered: May 2020
Posts: 304 |
Quoting ChristopherJamNah, crystal in a PAL c64 is nominally 17.734475MHz, which is divided by 18 to give a CPU clock of around 985kHz.
I know that.
By "same crystal" I meant same inaccuracy of about 6ppm. |
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