diff --git a/components/libc/compilers/armlibc/sys/types.h b/components/libc/compilers/armlibc/sys/types.h
index 2aad77c99db685d720cf8ccf3647a1ef7b15f910..78fee1bb999f28c94460b3bf330cbf38ccf61c64 100644
--- a/components/libc/compilers/armlibc/sys/types.h
+++ b/components/libc/compilers/armlibc/sys/types.h
@@ -5,20 +5,22 @@
  *
  * Change Logs:
  * Date           Author       Notes
- * 2020-09-05 Meco Man  fix bugs
+ * 2020-09-05     Meco Man     fix bugs
+ * 2020-12-16     Meco Man     add useconds_t
  */
 #ifndef __TYPES_H__
 #define __TYPES_H__
 
 #include <stdint.h>
 
-typedef int32_t clockid_t;
-typedef int32_t key_t;       /* Used for interprocess communication. */
-typedef int32_t pid_t;       /* Used for process IDs and process group IDs. */
+typedef int32_t          clockid_t;
+typedef int32_t          key_t;         /* Used for interprocess communication. */
+typedef int32_t          pid_t;         /* Used for process IDs and process group IDs. */
 #ifndef ARCH_CPU_64BIT
-typedef signed int   ssize_t;  /* Used for a count of bytes or an error indication. */
+typedef signed int       ssize_t;       /* Used for a count of bytes or an error indication. */
 #else
-typedef long signed int   ssize_t;  /* Used for a count of bytes or an error indication. */
+typedef long signed int  ssize_t;       /* Used for a count of bytes or an error indication. */
 #endif
+typedef unsigned long    useconds_t;    /* microseconds (unsigned) */
 
 #endif
diff --git a/components/libc/compilers/armlibc/sys/unistd.h b/components/libc/compilers/armlibc/sys/unistd.h
index 549771e8f472eb6a16c8cd004fac05f3fba0b559..73a73a267e052233f9236a88ef9aead01778f4f0 100644
--- a/components/libc/compilers/armlibc/sys/unistd.h
+++ b/components/libc/compilers/armlibc/sys/unistd.h
@@ -5,11 +5,13 @@
  *
  * Change Logs:
  * Date           Author       Notes
+ * 2020-12-16     Meco Man     add usleep
  */
 #ifndef _SYS_UNISTD_H
 #define _SYS_UNISTD_H
 
-#include <rtthread.h>
+#include <rtconfig.h>
+#include "types.h"
 
 #ifdef RT_USING_DFS
 
@@ -69,5 +71,6 @@ int     isatty      (int fd);
 char *  ttyname     (int desc);
 
 unsigned int sleep(unsigned int seconds);
+int usleep(useconds_t usec);
 
 #endif /* _SYS_UNISTD_H */
diff --git a/components/libc/compilers/dlib/sys/types.h b/components/libc/compilers/dlib/sys/types.h
index 001ace4dd28e5b132486bed253cfea66ff17a3ff..7dbeddcaa96e2b2bc5246aec8c6e0572ff45314e 100644
--- a/components/libc/compilers/dlib/sys/types.h
+++ b/components/libc/compilers/dlib/sys/types.h
@@ -5,20 +5,21 @@
  *
  * Change Logs:
  * Date           Author       Notes
+ * 2020-12-16     Meco Man     add useconds_t
  */
 #ifndef __TYPES_H__
 #define __TYPES_H__
 
 #include <stdint.h>
-#include <rtthread.h>
 
-typedef rt_int32_t clockid_t;
-typedef rt_int32_t key_t;       /* Used for interprocess communication. */
-typedef rt_int32_t pid_t;       /* Used for process IDs and process group IDs. */
+typedef int32_t          clockid_t;
+typedef int32_t          key_t;         /* Used for interprocess communication. */
+typedef int32_t          pid_t;         /* Used for process IDs and process group IDs. */
 #ifndef ARCH_CPU_64BIT
-typedef signed int   ssize_t;  /* Used for a count of bytes or an error indication. */
+typedef signed int       ssize_t;       /* Used for a count of bytes or an error indication. */
 #else
-typedef long signed int   ssize_t;  /* Used for a count of bytes or an error indication. */
+typedef long signed int  ssize_t;       /* Used for a count of bytes or an error indication. */
 #endif
+typedef unsigned long    useconds_t;    /* microseconds (unsigned) */
 
 #endif
diff --git a/components/libc/compilers/dlib/sys/unistd.h b/components/libc/compilers/dlib/sys/unistd.h
index 982a29135dc360e776972978fbc49e5d409631ad..6d99cd6c55a48a7be4ae333c6b2ad4273536db0c 100644
--- a/components/libc/compilers/dlib/sys/unistd.h
+++ b/components/libc/compilers/dlib/sys/unistd.h
@@ -5,10 +5,14 @@
  *
  * Change Logs:
  * Date           Author       Notes
+ * 2020-12-16     Meco Man     add usleep
  */
 #ifndef _SYS_UNISTD_H
 #define _SYS_UNISTD_H
 
+#include <rtconfig.h>
+#include "types.h"
+
 #ifdef RT_USING_DFS
 
 #define STDIN_FILENO    0       /* standard input file descriptor */
@@ -41,5 +45,6 @@ int     isatty      (int fd);
 char *  ttyname     (int desc);
 
 unsigned int sleep(unsigned int seconds);
+int usleep(useconds_t usec);
 
 #endif /* _SYS_UNISTD_H */
diff --git a/components/libc/time/posix_sleep.c b/components/libc/time/posix_sleep.c
index f21b0a7994a384fb55f8724b3a9373255c81db67..d45b3b945f0a5992544724548fc2f398709317bf 100644
--- a/components/libc/time/posix_sleep.c
+++ b/components/libc/time/posix_sleep.c
@@ -5,10 +5,9 @@
  *
  * Change Logs:
  * Date           Author       Notes
+ * 2020-12-16     Meco Man     add usleep
  */
-#include <stdlib.h>
 #include <rtthread.h>
-
 #include <unistd.h>
 
 unsigned int sleep(unsigned int seconds)
@@ -21,3 +20,8 @@ unsigned int sleep(unsigned int seconds)
 
     return seconds - delta_tick/RT_TICK_PER_SECOND;
 }
+
+int usleep(useconds_t usec)
+{
+    
+}