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How is the xor.b #01,&p1out encoded? It would still potentially
disassemble correctly if it didn't use the register for the #01, but
would then require 3 words. As Jon says, that would still only recover 1
clock for you. I haven't tried this myself, so don't know what else
might be added but can you stop the process after the reti.? A break on
the xor.b might change the behaviour, if so, perhaps move the LPM3 start
instruction there and see what happens.
Al
On 18/09/2015 4:57 AM, 'Redd, Emmett R' [email protected]
[msp430] wrote:
> I am using Tom Baugh's MSP430F2274 board and software in a class. We are also using IAR Kickstart.
>
> In his second lab exercise, BetterNextProject, we see various timing interrupt methods and LPM3 to reduce the number of cycles and power consumed. Each time the LED output, P1.0, toggles due to a timer firing its interrupt, the SMCLK can be seen making a burst of 28 cycles of running in active mode. Analyzing the disassembly code and reading the Family User's Guide, I can only account for 24 cycles.
>
> Here are the details:
>
> Action/Instruction (in execution order) Cycles (from Tables 3-14 & 16 in the Family User's Guide)
>
> Interrupt Accepted 6
> 008094 bic.w #0xF0, 0x0(SP) 5 // First line of WatchdogTimer_ISR. All low-power modes cleared.
> 00809A reti 5
> 008050 xor.b #0x1,&P1OUT 4 // Constant Generator register source to absolute destination.
> // This toggles the LED.
> 008054 jmp 0x804C 2 // End of While Loop.
>
> 00804C bis.w #0xD8,SR 2 // Beginning of While Loop. Start LPM3. Instruction immediately
> ___ //before the XOR.
> Total 24 cycles
>
> When I monitor SMCLK on P2.1 on an oscilloscope, it idles high and has 28 falling edges. In addition, the LED toggles on the 22nd falling edge.
>
> I count 24 cycles in the code, but measure 28 on the oscilloscope. (And I count 20 until the end of the instruction toggling the LED but measure it occurring on the 22nd falling edge.
>
> So, what am I missing?
>
> Thanks,
>
> Emmett Redd Ph.D. mailto:[email protected]
> Professor (417)836-5221
> Department of Physics, Astronomy, and Materials Science
> Missouri State University Fax (417)836-6226
> 901 SOUTH NATIONAL Lab (417)836-3770
> SPRINGFIELD, MO 65897 USA Dept (417)836-5131
>
> In statesmanship get the formalities right, never mind about the moralities. -- Mark Twain.
>
>
> ------------------------------------
> Posted by: "Redd, Emmett R" <[email protected]>
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