Hi,

I am writing some code for a software spi interface (its funny spi 15 1/2 bits)..

I am having some problems with a timing issue..

In GHS muti 2000 if i write a small piece of code eg
time=0
set_rtc(time); // set rtc to zero
print(time); // dump rtc value on lcd
i=1000000;
while(i--); // wait 20,000,000 cycles
time=get_rtc(); // shoud be 1 second or less... getting 5 seconds at 200mhz
print(time); // dump rtc value on lcd

and the clocks are setup for max speed set_clock_speed(C200_100_50)
the compiler generates 20 line of asm for the loop.

So if 1 instruction per cycle it should complete the loop in 20000000 cycles, 20ms...

Even if some of the instructions are 2 cycles its still not correct...


it takes 5 seconds to complete the loop!

Setting the clock to the slowest setting CPU=33 etc it take 13 seconds


I have read the CPUCLK reg back and it does say its set to 199987200 which is corected, or 33mhz for min clock speed.


It seem like the cpu is running at 4MHZ ish..

I do have a jtag debugger atatched but i understand this has no effect on the cpu speed, or does it?
Can anyone explain whats going on?
I have a PIC that can do this loop faster!!


Please understand i am not a asembly lang programmer, and also i do not want to use this code as a delay loop, its only an example to get the cpu to do something for a set time with the least number of cycles, i also understand that the rtc is prob not acurate, but i do get the same time value every time i run the code.


Help!