yes!

include/rp6502.h

@@ -96,11 +96,12 @@ long __fastcall__ ria_call_long (unsigned char op);
 #define RIA_OP_LRAND 0x04
 #define RIA_OP_STDIN_OPT 0x05
 #define RIA_OP_ERRNO_OPT 0x06
+#define RIA_OP_TZSET 0x0D
+#define RIA_OP_TZQUERY 0x0E
 #define RIA_OP_CLOCK 0x0F
 #define RIA_OP_CLOCK_GETRES 0x10
 #define RIA_OP_CLOCK_GETTIME 0x11
 #define RIA_OP_CLOCK_SETTIME 0x12
-#define RIA_OP_CLOCK_GETTIMEZONE 0x13
 #define RIA_OP_OPEN 0x14
 #define RIA_OP_CLOSE 0x15
 #define RIA_OP_READ_XSTACK 0x16

include/time.h

@@ -108,6 +108,7 @@ struct tm* __fastcall__ localtime (const time_t* timep);
 time_t __fastcall__ mktime (struct tm* timep);
 size_t __fastcall__ strftime (char* buf, size_t bufsize, const char* format, const struct tm* tm);
 time_t __fastcall__ time (time_t* t);
+void tzset (void);
 
 
 #if __CC65_STD__ >= __CC65_STD_CC65__
@@ -124,13 +125,10 @@ struct timespec {
 extern struct _timezone {
     char    daylight;   /* True if daylight savings time active */
     long    timezone;   /* Number of seconds behind UTC */
-    char    tzname[5];  /* Name of timezone, e.g. CET */
-    char    dstname[5]; /* Name when daylight true, e.g. CEST */
+    char    tzname[6];  /* Name of timezone, e.g. CET */
+    char    dstname[6]; /* Name when daylight true, e.g. CEST */
 } _tz;
 
-/* Set _tz for a specific time, if supported by target */
-void __fastcall__ tzset_time (time_t* t);
-
 #define CLK_TCK                 CLOCKS_PER_SEC
 
 /* POSIX function prototypes */

libsrc/common/localtime.s

@@ -5,9 +5,9 @@
 ;
 
         .export         _localtime
-        .import         __time_t_to_tm, __tz, _tzset_time
+        .import         __time_t_to_tm, __tz
         .import         ldeaxi, tosaddeax, pusheax
-        .importzp       sreg, ptr1
+        .importzp       sreg
 
 _localtime:
         cpx     #$00            ; Check for null pointer
@@ -16,7 +16,6 @@ _localtime:
         beq     no_pointer
 :       jsr     ldeaxi          ; Load value
         jsr     pusheax         ; Push it
-        jsr     _tzset_time
         lda     __tz+1+3
         sta     sreg+1
         lda     __tz+1+2
@@ -24,13 +23,7 @@ _localtime:
         ldx     __tz+1+1
         lda     __tz+1
         jsr     tosaddeax       ; Add _tz.timezone
-        jsr     __time_t_to_tm  ; Convert to struct tm
-        sta     ptr1            ; Returned tm pointer
-        stx     ptr1+1
-        ldy     #16
-        lda     __tz+0          ; Load _tz.daylight
-        sta     (ptr1),y        ; Store to tm.tm_isdst
-        lda     ptr1
+       jmp     __time_t_to_tm   ; Convert to struct tm
 
 no_pointer:
         rts                     ; A/X already set

libsrc/rp6502/gettimezone.c

@@ -1,17 +0,0 @@
-#include <rp6502.h>
-#include <time.h>
-
-int clock_gettimezone (time_t time, clockid_t clock_id, struct _timezone* tz)
-{
-    int ax;
-    ria_set_ax (clock_id);
-    ria_push_long (time);
-    ax = ria_call_int (RIA_OP_CLOCK_GETTIMEZONE);
-    if (ax >= 0) {
-        char i;
-        for (i = 0; i < sizeof (struct _timezone); i++) {
-            ((char*)tz)[i] = ria_pop_char ();
-        }
-    }
-    return ax;
-}

libsrc/rp6502/localtime.s

@@ -0,0 +1,12 @@
+;
+; struct tm* __fastcall__ localtime (const time_t* timep);
+;
+
+        .export         _localtime
+
+        .import         __localtime
+
+
+;--------------------------------------------------------------------------
+
+_localtime = __localtime

libsrc/rp6502/localtime_.c

@@ -0,0 +1,31 @@
+#include <rp6502.h>
+#include <time.h>
+#include <stdbool.h>
+
+static bool tzset_set = false;
+
+struct tm* __fastcall__ _time_t_to_tm (const time_t t);
+
+struct tm* __fastcall__ _localtime (const time_t* timep)
+{
+    long time = *timep;
+    struct tm* tm;
+    ria_set_axsreg (*timep);
+    time += ria_call_long (RIA_OP_TZQUERY);
+    tm = _time_t_to_tm (time);
+    tm->tm_isdst = ria_pop_char ();
+    if (!tzset_set) { tzset (); }
+    return tm;
+}
+
+void tzset (void)
+{
+    int ax = ria_call_int (RIA_OP_TZSET);
+    if (ax >= 0) {
+        char i;
+        for (i = 0; i < sizeof (struct _timezone); i++) {
+            ((char*)&_tz)[i] = ria_pop_char ();
+        }
+        tzset_set = true;
+    }
+}

libsrc/rp6502/tzset_time.s

@@ -1,26 +0,0 @@
-; tzset_time.s
-;
-; This file is part of
-; cc65 - a freeware C compiler for 6502 based systems
-;
-; https://cc65.github.io
-;
-; See "LICENSE" file for legal information.
-;
-; void __fastcall__ tzset_time (time_t* time);
-;
-
-        .export         _tzset_time
-        .import         _clock_gettimezone, __tz
-        .import         pushax, ldax0sp, ldeaxi, pusheax, pusha, incsp2
-        .include        "time.inc"
-
-
-_tzset_time:
-        jsr     ldeaxi
-        jsr     pusheax
-        lda     #CLOCK_REALTIME
-        jsr     pusha
-        lda     #<(__tz)
-        ldx     #>(__tz)
-        jmp     _clock_gettimezone