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MCF5307, execution speed question

Question asked by Angelo Dureghello on Nov 17, 2012
Latest reply on Nov 19, 2012 by TomE

Hi all,

i have a MCF5307 based custom board set with 45Mhz oscillator, 90Mhz CPU CLOK (x2) and 45 Mhz BUS_CLK (div. 2).

 

I am measuring through oscilloscope the length of some basic instructions (in time) to see if the execution speed is really 90Mhz, since i have some doubts on this.

 

move.w #AAAA, (ADDR_PADAT) ( i am producing a square wave on PADAT)

For this single "move.w #xxx, (A)" i get 360ns with cache disabled, or 132ns with cache enabled or internal dram.

This instruction should take 2 clocks, so i was expecting 11,1 nsec  x 2 = 22 nsecs.

 

Then i measured, always executing from internal ram, a single short jmp. It takes 50nsecs.

But i was ecpecting 11nsecs (1 clock).

 

Then i measured the output clock on PSTCLK (delayed CPU clock). It is 90Mhz, as expected.

 

Can someone maybe elucidate me on this long instruction timings ?

 

Many thanks

Angelo

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