Replaced _systime with clock_gettime.

We want to add the capability to not only get the time but also set the time, but there's no "setter" for the "getter" time().

The first ones that come into mind are gettimeofday() and settimeofday(). However, they take a struct timezone argument that doesn't make sense - even the man pages says "The use of the timezone structure is obsolete; the tz argument should normally be specified as NULL." And POSIX says "Applications should use the clock_gettime() function instead of the obsolescent gettimeofday() function."

The ...timeofday() functions work with microseconds while the clock_...time() functions work with nanoseconds. Given that we expect our targets to support only 1/10 of seconds the microseconds look preferable at first sight. However, already microseconds require the cc65 data type 'long' so it's not such a relevant difference to nanoseconds. Additionally clock_getres() seems useful.

In order to avoid code duplication clock_gettime() takes over the role of the actual time getter from _systime(). So time() now calls clock_gettime() instead of _systime().

For some reason beyond my understanding _systime() was mentioned in time.h. _systime() worked exactly like e.g. _sysremove() and those _sys...() functions are all considered internal. The only reason I could see would be a performance gain of bypassing the time() wrapper. However, all known _systime() implementations internally called mktime(). And mktime() is implemented in C using an iterative algorithm so I really can't see what would be left to gain here. From that perspective I decided to just remove _systime().

libsrc/c64/gettime.s

@@ -1,27 +1,27 @@
 ;
 ; Stefan Haubenthal, 27.7.2009
+; Oliver Schmidt, 14.8.2018
 ;
-; time_t _systime (void);
-; /* Similar to time(), but:
-; **   - Is not ISO C
-; **   - Does not take the additional pointer
-; **   - Does not set errno when returning -1
-; */
+; int clock_gettime (clockid_t clk_id, struct timespec *tp);
 ;
 
         .include        "time.inc"
         .include        "c64.inc"
         .include        "get_tv.inc"
 
-        .constructor    initsystime
-        .importzp       tmp1, tmp2
+        .constructor    inittime
+        .importzp       sreg, tmp1, tmp2
+        .import         pushax, pusheax, tosmul0ax, steaxspidx, incsp1, return0
         .import         _get_tv, _get_ostype
 
 
 ;----------------------------------------------------------------------------
 .code
 
-.proc   __systime
+.proc   _clock_gettime
+
+        jsr     pushax
+        jsr     pushax
 
         lda     CIA1_TODHR
         bpl     AM
@@ -38,13 +38,38 @@ AM:     jsr     BCD2dec
         lda     CIA1_TODSEC
         jsr     BCD2dec
         sta     TM + tm::tm_sec
-        lda     CIA1_TOD10              ; Dummy read to unfreeze
         lda     #<TM
         ldx     #>TM
-        jmp     _mktime
+        jsr     _mktime
 
+        ldy     #timespec::tv_sec
+        jsr     steaxspidx      ; Pops address pushed by 2. pushax
+
+        lda     #<(100 * 1000 * 1000 / $10000)
+        ldx     #>(100 * 1000 * 1000 / $10000)
+        sta     sreg
+        stx     sreg+1
+        lda     #<(100 * 1000 * 1000)
+        ldx     #>(100 * 1000 * 1000)
+        jsr     pusheax
+        lda     CIA1_TOD10
+        ldx     #>$0000
+        jsr     tosmul0ax
+
+        ldy     #timespec::tv_nsec
+        jsr     steaxspidx      ; Pops address pushed by 1. pushax
+
+        jsr     incsp1
+        jmp     return0
+
+.endproc
+
+;----------------------------------------------------------------------------
 ; dec = (((BCD>>4)*10) + (BCD&0xf))
-BCD2dec:tax
+
+.proc   BCD2dec
+
+        tax
         and     #%00001111
         sta     tmp1
         txa
@@ -65,7 +90,7 @@ BCD2dec:tax
 ; and write it again, ignoring a possible change in between.
 .segment "ONCE"
 
-.proc   initsystime
+.proc   inittime
 
         lda     CIA1_TOD10
         sta     CIA1_TOD10