Propeller System Clock

ImmNek

Hi guys,

You guess right, I have a question related to the system clock of the propeller chip.

I read in the manual, that the internal PLL frequency is generated by 16 times the crystal frequency. And I read too, that the PLL frequency must be from 64MHz to 128MHz. So I connected a 8MHz crystal to my chip and set the clockmode to xtal1 and pll16x. Then I tested the chip loading it with some ASM-code and it works. But when I tried to run some SPIN-code, strange things happened on my chip. Can somebody explane me this effect, please?

Thanks a lot
Immanuel

BradC

ImmNek said...
Hi guys,

You guess right, I have a question related to the system clock of the propeller chip.

I read in the manual, that the internal PLL frequency is generated by 16 times the crystal frequency. And I read too, that the PLL frequency must be from 64MHz to 128MHz. So I connected a 8MHz crystal to my chip and set the clockmode to xtal1 and pll16x. Then I tested the chip loading it with some ASM-code and it works. But when I tried to run some SPIN-code, strange things happened on my chip. Can somebody explane me this effect, please?

Thanks a lot
Immanuel

You are running the processor at 128 MHZ. This is well over the rated operating speed of 80MHZ, so I'd suspect the chip is doing unpredictable things.
Try it at 8 * PLLX8 and see if it stable.

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Pull my finger!

heater

I have a Prop with a 10MHz XTAL and use PLLX8, runs just fine.

Strangely I tried a bunch of slower crystals down to 5MHz and none of them worked. Could be my wonky home made demo board construction though.

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For me, the past is not over yet.

ImmNek

I tried it with pll8x and it works. But why ASM-code works on 128MHz?

Mike Green

At higher clock speeds, certain parts of the chip fail before others. The Spin interpreter, because it's written very tightly, tends to use as much of the capability of the chip as possible while your assembly routine may not use some instructions that are affected early by the over-clocking.

Rayman

The original PropOled96 has a 8MHz crystal and ran SPIN code in one cog fine at PLL16x.· But, as soon as you try using multiple cogs, it fails...

ImmNek

Thanks a lot, your answer make sens to me.

hippy

@ ImmNek : You may also find this information on the Propeller Wiki useful ...

propeller.wikispaces.com/Oscillator

ImmNek

@ hippy:
Thanks a lot for your link. It's very useful.