[cc65] gettimeofday()

From: Karri Kaksonen <karri1sipo.fi>
Date: 2012-01-18 20:01:22
This discussion about interrupts remind me of how to manage the real 
time clock in games.

In some variants of C I have seen a function that can track time down to 
microseconds called


     gettimeofday - get the date and time


     #include <sys/time.h>

     int gettimeofday(struct timeval *restrict tp, void *restrict tzp);


     The gettimeofday() function shall obtain the current time, 
expressed as seconds and microseconds since the Epoch, and store it in 
the timeval structure pointed to by tp. The resolution of the system 
clock is unspecified.

     If tzp is not a null pointer, the behavior is unspecified.


     The gettimeofday() function shall return 0 and no value shall be 
reserved to indicate an error.


     No errors are defined.

The <sys/time.h> header shall define the timeval structure that includes 
at least the following members:

time_t         tv_sec      Seconds.
suseconds_t    tv_usec     Microseconds.

The tv_usec needs to hold values from 0 to 999999
The tv_sec just needs to be able to show seconds. This can start from 0 
if no realtime clock is availabe and from EPOCH if a realtime clock exists.

So every time I get a VBL interrupt in the Lynx I could add 13333 us to 

         .interruptor system_clock_irq

         lda     INTSET          ; Poll all pending interrupts
         and     #VBL_INTERRUPT
         beq     irqend          ; Exit if not a VBL interrupt
         ... write code to increment tv_usec tv_sec by 13333 usec

Would this be a good addition to the C-library? At least it is more 
usable in games than time().


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Received on Wed Jan 18 20:35:13 2012

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