diff --git a/asminc/rp6502.inc b/asminc/rp6502.inc
index c3cec2182..05dc93cbe 100644
--- a/asminc/rp6502.inc
+++ b/asminc/rp6502.inc
@@ -50,8 +50,28 @@ RIA_OP_READ_XRAM          := $17
 RIA_OP_WRITE_XSTACK       := $18
 RIA_OP_WRITE_XRAM         := $19
 RIA_OP_LSEEK              := $1A
+RIA_OP_LSEEK_CC65         := $1A
 RIA_OP_UNLINK             := $1B
 RIA_OP_RENAME             := $1C
+RIA_OP_LSEEK_LLVM         := $1D
+RIA_OP_SYNCFS             := $1E
+RIA_OP_STAT               := $1F
+RIA_OP_OPENDIR            := $20
+RIA_OP_READDIR            := $21
+RIA_OP_CLOSEDIR           := $22
+RIA_OP_TELLDIR            := $23
+RIA_OP_SEEKDIR            := $24
+RIA_OP_REWINDDIR          := $25
+RIA_OP_CHMOD              := $26
+RIA_OP_UTIME              := $27
+RIA_OP_MKDIR              := $28
+RIA_OP_CHDIR              := $29
+RIA_OP_CHDRIVE            := $2A
+RIA_OP_GETCWD             := $2B
+RIA_OP_SETLABEL           := $2C
+RIA_OP_GETLABEL           := $2D
+RIA_OP_GETFREE            := $2E
+
 
 ; 6522 VIA
 VIA             := $FFD0        ; VIA base address
diff --git a/include/rp6502.h b/include/rp6502.h
index c443bd8f9..b51382825 100644
--- a/include/rp6502.h
+++ b/include/rp6502.h
@@ -108,22 +108,58 @@ long __fastcall__ ria_call_long (unsigned char op);
 #define RIA_OP_WRITE_XSTACK 0x18
 #define RIA_OP_WRITE_XRAM 0x19
 #define RIA_OP_LSEEK 0x1A
+#define RIA_OP_LSEEK_CC65 0x1A
 #define RIA_OP_UNLINK 0x1B
 #define RIA_OP_RENAME 0x1C
+#define RIA_OP_LSEEK_LLVM 0x1D
+#define RIA_OP_SYNCFS 0x1E
+#define RIA_OP_STAT 0x1F
+#define RIA_OP_OPENDIR 0x20
+#define RIA_OP_READDIR 0x21
+#define RIA_OP_CLOSEDIR 0x22
+#define RIA_OP_TELLDIR 0x23
+#define RIA_OP_SEEKDIR 0x24
+#define RIA_OP_REWINDDIR 0x25
+#define RIA_OP_CHMOD 0x26
+#define RIA_OP_UTIME 0x27
+#define RIA_OP_MKDIR 0x28
+#define RIA_OP_CHDIR 0x29
+#define RIA_OP_CHDRIVE 0x2A
+#define RIA_OP_GETCWD 0x2B
+#define RIA_OP_SETLABEL 0x2C
+#define RIA_OP_GETLABEL 0x2D
+#define RIA_OP_GETFREE 0x2E
 
 /* C API for the operating system. */
 
+typedef struct {
+    unsigned long fsize;    /* File size (invalid for directory) */
+    unsigned fdate;         /* Date of file modification or directory creation */
+    unsigned ftime;         /* Time of file modification or directory creation */
+    unsigned crdate;        /* Date of object createion */
+    unsigned crtime;        /* Time of object createion */
+    unsigned char fattrib;  /* Object attribute */
+    char altname[12 + 1];   /* Alternative object name */
+    char fname[255 + 1];    /* Primary object name */
+} f_stat_t;
+
 int __cdecl__ xregn (char device, char channel, unsigned char address, unsigned count,
     ...);
 int __cdecl__ xreg (char device, char channel, unsigned char address, ...);
-int phi2 (void);
-int codepage (int);
-long lrand (void);
+int __fastcall__ phi2 (void);
+int __fastcall__ codepage (int);
+long __fastcall__ lrand (void);
 int __fastcall__ stdin_opt (unsigned long ctrl_bits, unsigned char str_length);
 int __fastcall__ read_xstack (void* buf, unsigned count, int fildes);
 int __fastcall__ read_xram (unsigned buf, unsigned count, int fildes);
 int __fastcall__ write_xstack (const void* buf, unsigned count, int fildes);
 int __fastcall__ write_xram (unsigned buf, unsigned count, int fildes);
+long __fastcall__ f_lseek (long offset, int whence, int fildes);
+int __fastcall__ f_stat (const char* path, f_stat_t* dirent);
+int __fastcall__ f_opendir (const char* name);
+int __fastcall__ f_readdir (f_stat_t *dirent, int dirdes);
+int __fastcall__ f_closedir (int dirdes);
+
 
 /* Time zone hack */
 
diff --git a/include/unistd.h b/include/unistd.h
index 05b60f1fd..d48fe6f31 100644
--- a/include/unistd.h
+++ b/include/unistd.h
@@ -77,6 +77,7 @@ extern int optind, opterr, optopt;
 int __fastcall__ write (int fd, const void* buf, unsigned count);
 int __fastcall__ read (int fd, void* buf, unsigned count);
 off_t __fastcall__ lseek (int fd, off_t offset, int whence);
+int __fastcall__ syncfs (int fd);
 int __fastcall__ unlink (const char* name);     /* Same as remove() */
 
 /* Directories */
@@ -98,6 +99,3 @@ int __fastcall__ exec (const char* progname, const char* cmdline);
 
 /* End of unistd.h */
 #endif
-
-
-
diff --git a/libsrc/rp6502/f_closedir.c b/libsrc/rp6502/f_closedir.c
new file mode 100644
index 000000000..03239c874
--- /dev/null
+++ b/libsrc/rp6502/f_closedir.c
@@ -0,0 +1,8 @@
+#include <rp6502.h>
+#include <fcntl.h>
+
+int __fastcall__ f_closedir (int dirdes)
+{
+    ria_set_ax (dirdes);
+    return ria_call_int (RIA_OP_CLOSEDIR);
+}
diff --git a/libsrc/rp6502/f_lseek.c b/libsrc/rp6502/f_lseek.c
new file mode 100644
index 000000000..da7c3dfdf
--- /dev/null
+++ b/libsrc/rp6502/f_lseek.c
@@ -0,0 +1,10 @@
+#include <rp6502.h>
+#include <unistd.h>
+
+long __fastcall__ f_lseek (long offset, int whence, int fildes)
+{
+    ria_set_ax (fildes);
+    ria_push_long (offset);
+    ria_push_char (whence);
+    return ria_call_long (RIA_OP_LSEEK);
+}
diff --git a/libsrc/rp6502/f_opendir.c b/libsrc/rp6502/f_opendir.c
new file mode 100644
index 000000000..29faf776e
--- /dev/null
+++ b/libsrc/rp6502/f_opendir.c
@@ -0,0 +1,16 @@
+#include <rp6502.h>
+#include <errno.h>
+#include <string.h>
+
+int __fastcall__ f_opendir (const char* name)
+{
+    size_t namelen = strlen (name);
+    if (namelen > 255) {
+        errno = EINVAL;
+        return -1;
+    }
+    while (namelen) {
+        ria_push_char (name[--namelen]);
+    }
+    return ria_call_int (RIA_OP_OPENDIR);
+}
diff --git a/libsrc/rp6502/f_readdir.c b/libsrc/rp6502/f_readdir.c
new file mode 100644
index 000000000..f6fa42e1b
--- /dev/null
+++ b/libsrc/rp6502/f_readdir.c
@@ -0,0 +1,14 @@
+#include <rp6502.h>
+#include <errno.h>
+#include <string.h>
+
+int __fastcall__ f_readdir (f_stat_t *dirent, int dirdes)
+{
+    int i, ax;
+    ria_set_ax (dirdes);
+    ax = ria_call_int (RIA_OP_READDIR);
+    for (i = 0; i < sizeof (f_stat_t); i++) {
+        ((char*)dirent)[i] = ria_pop_char ();
+    }
+    return ax;
+}
diff --git a/libsrc/rp6502/f_stat.c b/libsrc/rp6502/f_stat.c
new file mode 100644
index 000000000..3e3845639
--- /dev/null
+++ b/libsrc/rp6502/f_stat.c
@@ -0,0 +1,21 @@
+#include <rp6502.h>
+#include <errno.h>
+#include <string.h>
+
+int __fastcall__ f_stat (const char* path, f_stat_t* dirent)
+{
+    int i, ax;
+    size_t pathlen = strlen (path);
+    if (pathlen > 255) {
+        errno = EINVAL;
+        return -1;
+    }
+    while (pathlen) {
+        ria_push_char (path[--pathlen]);
+    }
+    ax = ria_call_int (RIA_OP_STAT);
+    for (i = 0; i < sizeof (f_stat_t); i++) {
+        ((char*)dirent)[i] = ria_pop_char ();
+    }
+    return ax;
+}
diff --git a/libsrc/rp6502/lseek.c b/libsrc/rp6502/lseek.c
index caddb9bf6..a40c7318d 100644
--- a/libsrc/rp6502/lseek.c
+++ b/libsrc/rp6502/lseek.c
@@ -3,7 +3,6 @@
 
 off_t __fastcall__ lseek (int fd, off_t offset, int whence)
 {
-    /* Modified argument order for short stacking offset */
     ria_push_long (offset);
     ria_push_char (whence);
     ria_set_ax (fd);
diff --git a/libsrc/rp6502/syncfs.c b/libsrc/rp6502/syncfs.c
new file mode 100644
index 000000000..34c12a8f6
--- /dev/null
+++ b/libsrc/rp6502/syncfs.c
@@ -0,0 +1,8 @@
+#include <rp6502.h>
+#include <unistd.h>
+
+int __fastcall__ syncfs (int fd)
+{
+    ria_set_ax (fd);
+    return ria_call_int (RIA_OP_SYNCFS);
+}
diff --git a/libsrc/rp6502/write_xram.c b/libsrc/rp6502/write_xram.c
index 7251cdd43..0a46ec62c 100644
--- a/libsrc/rp6502/write_xram.c
+++ b/libsrc/rp6502/write_xram.c
@@ -2,8 +2,8 @@
 
 int __fastcall__ write_xram (unsigned buf, unsigned count, int fildes)
 {
+    ria_set_ax (fildes);
     ria_push_int (buf);
     ria_push_int (count);
-    ria_set_ax (fildes);
     return ria_call_int (RIA_OP_WRITE_XRAM);
 }