I would very much appreciate if anyone could provide code for a reliable 10,000 instruction cycle delay routine for AVR GCC (in either asm or C). I have been banging my head all day against GCC inline assembly and getting no where! I find it to be an incredibly criptic language with little documentation. I would really, really appreciate any help.
Thanks! Sam
Why don't you use timers? Most AVRs have at least one.
There's lots of documentation. Where are you looking?
If I wanted to write a delay loop, in avr-gcc, I'd look for something in the library with the string 'delay' in it. Y'know, like delay.h?
Googling "avr libc delay" (without the quotes) gives
Something like
#include ... _delay_loop_2(2500);
should work nicely.
If you want to delay for a period of time measured in microseconds rather than machine cycles, and you have a 1MHz clock, you can use
#define F_CPU 1000000 #include ... delay_us(10000)
That way you can change your oscillator but keep your delay loops the same length by updating the value for F_CPU and recompiling. In my makefile, I would set F_CPU on the compiler command line in the makefile using -D.
Note: older versions of the library have this in
Regards, -=Dave
-- Change is inevitable, progress is not.
Why do anything simple way when one can make it complex and wonderful?
I think some people simply have a problem thinking outside of the box. That things like interrupts and hardware timers are exotic, frightening, and best avoided, no matter that they are already there, paid for, whether they are used or not.
The nop-loop style delays are going to be reliable only as long as there are no interrupt service routines firing during the delay period. If the delay is long and the interrupts are badly predictable (say input change interrupts), the interrupt service routines will consume a considerable and variable amount of the cycles. Disabling all interrupts may be a solution in some cases, however, this might not be an option if long delays are needed.
If the processor contains a true clock cycle counter, like the TSC on Pentiums, it should be easy to monitor it until the required count has been reached regardless of interrupts. Also any free running counter driven from a reliable source (say the UART clock) can be used. In these cases the wakeup can be delayed by only one interrupt service routine time.
Using a clock interrupt to count the time is problematic due to the lower granulaty, since the interrupt service routine interrupt rate must be quite low to allow for the execution of the clock interrupt service routine. One reasonable approach would be to use the clock interrupt just prior to the required wake up time and do the last step with a nop-loop, since the likelihood for multiple other interrupts would be quite small during the nop-loop.
Paul
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