diff --git a/bsp/gd32303e-eval/rtconfig.h b/bsp/gd32303e-eval/rtconfig.h
index 7a47c83787608ff322e4bb9a7e7ffb94c7b087ca..365fd296e062693a459631c35d3bdf3821084299 100644
--- a/bsp/gd32303e-eval/rtconfig.h
+++ b/bsp/gd32303e-eval/rtconfig.h
@@ -125,6 +125,7 @@
 /* POSIX layer and C standard library */
 
 #define RT_USING_LIBC
+#define RT_USING_POSIX
 #define RT_LIBC_USING_TIME
 #define RT_LIBC_DEFAULT_TIMEZONE 8
 /* end of POSIX layer and C standard library */
diff --git a/bsp/lm3s8962/applications/startup.c b/bsp/lm3s8962/applications/startup.c
index 87df6e8788d0c24ad6bb463fafa5d2cde892f16b..0742c5453ca140423b9d0ae0bc3012bc382d6f00 100644
--- a/bsp/lm3s8962/applications/startup.c
+++ b/bsp/lm3s8962/applications/startup.c
@@ -119,7 +119,7 @@ void rtthread_startup(void)
 #ifdef RT_USING_FINSH
     /* init finsh */
     finsh_system_init();
-#ifdef RT_USING_DEVICE
+#if !defined(RT_USING_LIBC) && defined(RT_USING_DEVICE)
     finsh_set_device("uart1");
 #endif
 #endif
diff --git a/bsp/lm3s8962/rtconfig.h b/bsp/lm3s8962/rtconfig.h
index b154688a6deaadf2750cb788792ee01bc63ee670..dd583205baf5c6940e85e28c0c5a9aa91f5451b9 100644
--- a/bsp/lm3s8962/rtconfig.h
+++ b/bsp/lm3s8962/rtconfig.h
@@ -75,8 +75,10 @@
 #define FINSH_USING_SYMTAB
 #define FINSH_USING_DESCRIPTION
 
+#define RT_USING_LIBC
 #define RT_USING_DFS
-/* SECTION: DFS options */
+#define RT_USING_POSIX
+#define RT_USING_DFS_DEVFS
 #define RT_USING_DFS_ELMFAT
 #define RT_DFS_ELM_WORD_ACCESS
 
@@ -144,6 +146,5 @@
 /* the size of each pbuf in the pbuf pool. */
 #define RT_LWIP_PBUF_POOL_BUFSIZE		1500
 
-#define RT_USING_LIBC
 #define RT_USING_LWIP141
 #endif
diff --git a/components/dfs/SConscript b/components/dfs/SConscript
index e449c849114ac9e88d1ba1d627f990901707da93..5a0b394ce2de5e19474327e942237eb788fd108f 100644
--- a/components/dfs/SConscript
+++ b/components/dfs/SConscript
@@ -5,14 +5,10 @@ src = Split('''
 src/dfs.c
 src/dfs_file.c
 src/dfs_fs.c
-src/dfs_posix.c
 ''')
 cwd = GetCurrentDir()
 CPPPATH = [cwd + "/include"]
 
-if GetDepend('RT_USING_POSIX'):
-    src += ['src/dfs_poll.c', 'src/dfs_select.c']
-
 group = DefineGroup('Filesystem', src, depend = ['RT_USING_DFS'], CPPPATH = CPPPATH)
 
 if GetDepend('RT_USING_DFS'):
diff --git a/components/dfs/src/dfs.c b/components/dfs/src/dfs.c
index 8155b088f0f38ef1c5dfe3b1463d8442bd138f16..fa93afd74959285d72525d1d11a62fded2818f2f 100644
--- a/components/dfs/src/dfs.c
+++ b/components/dfs/src/dfs.c
@@ -18,7 +18,7 @@
 #include <lwp.h>
 #endif
 
-#if defined(RT_USING_DFS_DEVFS) && defined(RT_USING_POSIX)
+#ifdef RT_USING_LIBC
 #include <libc.h>
 #endif
 
@@ -216,7 +216,7 @@ struct dfs_fd *fd_get(int fd)
     struct dfs_fd *d;
     struct dfs_fdtable *fdt;
 
-#if defined(RT_USING_DFS_DEVFS) && defined(RT_USING_POSIX)
+#ifdef RT_USING_LIBC
     if ((0 <= fd) && (fd <= 2))
         fd = libc_stdio_get_console();
 #endif
diff --git a/components/dfs/src/dfs_file.c b/components/dfs/src/dfs_file.c
index fa0f6000b440cd0d94dc08f7da351d8221cd5c82..978c1056c2ad5ffddb32a9a2afd023f70b7a2fe8 100644
--- a/components/dfs/src/dfs_file.c
+++ b/components/dfs/src/dfs_file.c
@@ -621,6 +621,7 @@ void cat(const char *filename)
 }
 FINSH_FUNCTION_EXPORT(cat, print file);
 
+#ifdef RT_USING_POSIX
 #define BUF_SZ  4096
 static void copyfile(const char *src, const char *dst)
 {
@@ -749,6 +750,7 @@ static const char *_get_path_lastname(const char *path)
     /* skip the '/' then return */
     return ++ptr;
 }
+
 void copy(const char *src, const char *dst)
 {
 #define FLAG_SRC_TYPE      0x03
@@ -841,7 +843,8 @@ void copy(const char *src, const char *dst)
     }
 }
 FINSH_FUNCTION_EXPORT(copy, copy file or dir)
+#endif /* RT_USING_POSIX */
 
-#endif
+#endif /* RT_USING_FINSH */
 /* @} */
 
diff --git a/components/finsh/SConscript b/components/finsh/SConscript
index 28fe02bac53de3fa8756714eaa43d2034baadb5f..5eabe47c0e00d63eee5147c6cd2b18020137ea56 100644
--- a/components/finsh/SConscript
+++ b/components/finsh/SConscript
@@ -9,7 +9,7 @@ msh.c
 if GetDepend('MSH_USING_BUILT_IN_COMMANDS'):
     src += ['cmd.c']
 
-if GetDepend('RT_USING_DFS'):
+if GetDepend('RT_USING_POSIX'):
     src += ['msh_file.c']
 
 CPPPATH = [cwd]
diff --git a/components/finsh/finsh.h b/components/finsh/finsh.h
index 98048ebad4301bfa0d31d062624618b2ff42559d..f5e4df9e493bb195c638efb4d37c822d47ad7acf 100644
--- a/components/finsh/finsh.h
+++ b/components/finsh/finsh.h
@@ -169,7 +169,7 @@ extern struct finsh_syscall *_syscall_table_begin, *_syscall_table_end;
 struct finsh_syscall *finsh_syscall_lookup(const char *name);
 
 #ifdef RT_USING_DEVICE
-    void finsh_set_device(const char *device_name);
+void finsh_set_device(const char *device_name);
 #endif
 
 #endif
diff --git a/components/finsh/msh.c b/components/finsh/msh.c
index 18182ca2646a094587c3cb9ad2c985550f06ce24..5cb54c26e720c727dde7f4e7791b2dd74aacbdf3 100644
--- a/components/finsh/msh.c
+++ b/components/finsh/msh.c
@@ -21,7 +21,7 @@
 #include "msh.h"
 #include "shell.h"
 
-#ifdef RT_USING_DFS
+#ifdef RT_USING_POSIX
     #include <dfs_posix.h>
 #endif
 
@@ -186,7 +186,7 @@ static cmd_function_t msh_get_cmd(char *cmd, int size)
     return cmd_func;
 }
 
-#if defined(RT_USING_MODULE) && defined(RT_USING_DFS)
+#if defined(RT_USING_MODULE) && defined(RT_USING_POSIX)
 /* Return 0 on module executed. Other value indicate error.
  */
 int msh_exec_module(const char *cmd_line, int size)
@@ -257,7 +257,7 @@ int msh_exec_module(const char *cmd_line, int size)
     rt_free(pg_name);
     return ret;
 }
-#endif /* defined(RT_USING_MODULE) && defined(RT_USING_DFS) */
+#endif /* defined(RT_USING_MODULE) && defined(RT_USING_POSIX) */
 
 static int _msh_exec_cmd(char *cmd, rt_size_t length, int *retp)
 {
@@ -290,7 +290,7 @@ static int _msh_exec_cmd(char *cmd, rt_size_t length, int *retp)
     return 0;
 }
 
-#if defined(RT_USING_LWP) && defined(RT_USING_DFS)
+#if defined(RT_USING_LWP) && defined(RT_USING_POSIX)
 static int _msh_exec_lwp(char *cmd, rt_size_t length)
 {
     int argc;
@@ -350,7 +350,7 @@ int msh_exec(char *cmd, rt_size_t length)
     {
         return cmd_ret;
     }
-#ifdef RT_USING_DFS
+#ifdef RT_USING_POSIX
 #ifdef DFS_USING_WORKDIR
     if (msh_exec_script(cmd, length) == 0)
     {
@@ -371,7 +371,7 @@ int msh_exec(char *cmd, rt_size_t length)
         return 0;
     }
 #endif /* RT_USING_LWP */
-#endif /* RT_USING_DFS */
+#endif /* RT_USING_POSIX */
 
     /* truncate the cmd at the first space. */
     {
@@ -400,7 +400,7 @@ static int str_common(const char *str1, const char *str2)
     return (str - str1);
 }
 
-#ifdef RT_USING_DFS
+#ifdef RT_USING_POSIX
 void msh_auto_complete_path(char *path)
 {
     DIR *dir = RT_NULL;
@@ -521,7 +521,7 @@ void msh_auto_complete_path(char *path)
     closedir(dir);
     rt_free(full_path);
 }
-#endif /* RT_USING_DFS */
+#endif /* RT_USING_POSIX */
 
 void msh_auto_complete(char *prefix)
 {
@@ -538,7 +538,7 @@ void msh_auto_complete(char *prefix)
         return;
     }
 
-#ifdef RT_USING_DFS
+#ifdef RT_USING_POSIX
     /* check whether a spare in the command */
     {
         char *ptr;
diff --git a/components/finsh/msh_file.c b/components/finsh/msh_file.c
index 8f067efd98645697427ef5102c9311bcbdc0fc3a..4e9ed53b31282200318d2f7c9181c9ddc99e4f39 100644
--- a/components/finsh/msh_file.c
+++ b/components/finsh/msh_file.c
@@ -11,7 +11,7 @@
 
 #include <rtthread.h>
 
-#if defined(RT_USING_FINSH) && defined(RT_USING_DFS)
+#if defined(RT_USING_FINSH) && defined(RT_USING_POSIX)
 
 #include <finsh.h>
 #include "msh.h"
@@ -702,5 +702,5 @@ static int cmd_tail(int argc, char **argv)
 }
 MSH_CMD_EXPORT_ALIAS(cmd_tail, tail, print the last N - lines data of the given file);
 
-#endif /* defined(RT_USING_FINSH) && defined(RT_USING_DFS) */
+#endif /* defined(RT_USING_FINSH) && defined(RT_USING_POSIX) */
 
diff --git a/components/finsh/shell.c b/components/finsh/shell.c
index 20f1bdef0ff335e4c8d43040b9c9166a5b66d6ef..292ea588cf08a1fba6ed402af1ff4a5c6484bb89 100644
--- a/components/finsh/shell.c
+++ b/components/finsh/shell.c
@@ -27,9 +27,9 @@
 #include "shell.h"
 #include "msh.h"
 
-#if defined(RT_USING_DFS)
-    #include <dfs_posix.h>
-#endif /* RT_USING_DFS */
+#ifdef RT_USING_POSIX
+#include <dfs_posix.h>
+#endif /* RT_USING_POSIX */
 
 /* finsh thread */
 #ifndef RT_USING_HEAP
@@ -104,7 +104,7 @@ const char *finsh_get_prompt(void)
     }
     strcpy(finsh_prompt, _MSH_PROMPT);
 
-#if defined(RT_USING_DFS) && defined(DFS_USING_WORKDIR)
+#if defined(RT_USING_POSIX) && defined(DFS_USING_WORKDIR)
     /* get current working directory */
     getcwd(&finsh_prompt[rt_strlen(finsh_prompt)], RT_CONSOLEBUF_SIZE - rt_strlen(finsh_prompt));
 #endif
@@ -145,7 +145,7 @@ void finsh_set_prompt_mode(rt_uint32_t prompt_mode)
 int finsh_getchar(void)
 {
 #ifdef RT_USING_DEVICE
-#ifdef RT_USING_POSIX
+#ifdef RT_USING_LIBC
     return getchar();
 #else
     char ch = 0;
@@ -163,14 +163,14 @@ int finsh_getchar(void)
         rt_sem_take(&shell->rx_sem, RT_WAITING_FOREVER);
 
     return ch;
-#endif /* RT_USING_POSIX */
+#endif /* RT_USING_LIBC */
 #else
     extern char rt_hw_console_getchar(void);
     return rt_hw_console_getchar();
 #endif /* RT_USING_DEVICE */
 }
 
-#if !defined(RT_USING_POSIX) && defined(RT_USING_DEVICE)
+#if !defined(RT_USING_LIBC) && defined(RT_USING_DEVICE)
 static rt_err_t finsh_rx_ind(rt_device_t dev, rt_size_t size)
 {
     RT_ASSERT(shell != RT_NULL);
@@ -436,7 +436,7 @@ void finsh_thread_entry(void *parameter)
     shell->echo_mode = 0;
 #endif
 
-#if !defined(RT_USING_POSIX) && defined(RT_USING_DEVICE)
+#if !defined(RT_USING_LIBC) && defined(RT_USING_DEVICE)
     /* set console device as shell device */
     if (shell->device == RT_NULL)
     {
diff --git a/components/finsh/shell.h b/components/finsh/shell.h
index 985d3b3fbd4db7cece6f401c098212a5064cf42e..598596ce00f398b8033c35e6318cf11e892f324f 100644
--- a/components/finsh/shell.h
+++ b/components/finsh/shell.h
@@ -78,7 +78,7 @@ struct finsh_shell
     rt_uint16_t line_position;
     rt_uint16_t line_curpos;
 
-#if !defined(RT_USING_POSIX) && defined(RT_USING_DEVICE)
+#if !defined(RT_USING_LIBC) && defined(RT_USING_DEVICE)
     rt_device_t device;
 #endif
 
diff --git a/components/libc/Kconfig b/components/libc/Kconfig
index b9600ef38987c98b711c5449ac928bba80cb1a79..812b1ce48c73226ec768cb2d2e6b76712cdef3c6 100644
--- a/components/libc/Kconfig
+++ b/components/libc/Kconfig
@@ -2,6 +2,8 @@ menu "POSIX layer and C standard library"
 
 config RT_USING_LIBC
     bool "Enable libc APIs from toolchain"
+    select RT_USING_DFS
+    select RT_USING_POSIX
     default y
 
 config RT_USING_PTHREADS
@@ -14,9 +16,9 @@ if RT_USING_PTHREADS
     default 8
 endif
 
-if RT_USING_LIBC && RT_USING_DFS
+if RT_USING_DFS
     config RT_USING_POSIX
-        bool "Enable POSIX layer for compatibility with UNIX APIs, poll/select etc"
+        bool "Enable POSIX layer, open/read/write/select etc"
         select RT_USING_DFS_DEVFS
         default y
 
@@ -49,9 +51,9 @@ if RT_USING_LIBC
         default n
 
     if RT_USING_MODULE
-    config RT_USING_CUSTOM_DLMODULE
-        bool "Enable load dynamic module by custom"
-        default n
+        config RT_USING_CUSTOM_DLMODULE
+            bool "Enable load dynamic module by custom"
+            default n
     endif
 
 endif
diff --git a/components/libc/compilers/common/SConscript b/components/libc/compilers/common/SConscript
index fbdb2f11ec39d3909dc27d092a9ede728d3653dd..b7a6626a3636ea73953f959b5213bda911eabbda 100644
--- a/components/libc/compilers/common/SConscript
+++ b/components/libc/compilers/common/SConscript
@@ -6,18 +6,15 @@ src   = []
 cwd   = GetCurrentDir()
 group = []
 CPPPATH = [cwd]
+CPPDEFINES = []
 
 if GetDepend('RT_USING_LIBC'):
     src += Glob('*.c')
-    if GetDepend('RT_USING_POSIX') == False:
-        SrcRemove(src, ['unistd.c', 'delay.c'])
 elif GetDepend('RT_LIBC_USING_TIME'):
     src += Glob('time.c')
 
 if rtconfig.CROSS_TOOL == 'keil':
-    CPPDEFINES = ['__CLK_TCK=RT_TICK_PER_SECOND']
-else:
-    CPPDEFINES = []
+    CPPDEFINES += ['__CLK_TCK=RT_TICK_PER_SECOND']
 
 group = DefineGroup('libc', src, depend = [], CPPPATH = CPPPATH, CPPDEFINES = CPPDEFINES)
 
diff --git a/components/libc/compilers/common/readme.md b/components/libc/compilers/common/readme.md
index 856ddeb0456ebea642bcc4ad5b6a91dcc595d0af..82e23f8970f5029e898fc6074abd148e65c36fb4 100644
--- a/components/libc/compilers/common/readme.md
+++ b/components/libc/compilers/common/readme.md
@@ -1,10 +1 @@
-## Attentions
-
-1. This folder is "common" for all toolchains.
-
-2. If you want to add new `.c` files, please do not forget to fix SConscript file too. eg:
-
-```python
-if GetDepend('RT_USING_POSIX') == False:
-        SrcRemove(src, ['unistd.c'])
-```
\ No newline at end of file
+This folder is "common" for all toolchains.
\ No newline at end of file
diff --git a/components/libc/compilers/common/unistd.c b/components/libc/compilers/common/unistd.c
deleted file mode 100644
index 9a457c42000426a69068b723d7e842243db0001d..0000000000000000000000000000000000000000
--- a/components/libc/compilers/common/unistd.c
+++ /dev/null
@@ -1,119 +0,0 @@
-/*
- * Copyright (c) 2006-2021, RT-Thread Development Team
- *
- * SPDX-License-Identifier: Apache-2.0
- *
- * Change Logs:
- * Date           Author       Notes
- * 2020-09-01     Meco Man     first Version
- * 2021-02-12     Meco Man     move all functions located in <pthread_sleep.c> to this file
- */
-
-#include <unistd.h>
-#include <rtthread.h>
-#include <rthw.h>
-
-#ifdef RT_USING_POSIX_TERMIOS
-#include "termios.h"
-int isatty(int fd)
-{
-    struct termios ts;
-    return(tcgetattr(fd, &ts) != -1); /*true if no error (is a tty)*/
-}
-#else
-int isatty(int fd)
-{
-    if (fd >=0 && fd < 3)
-    {
-        return 1;
-    }
-    else
-    {
-        return 0;
-    }
-}
-#endif
-RTM_EXPORT(isatty);
-
-char *ttyname(int fd)
-{
-    return "/dev/tty"; /* TODO: need to add more specific */
-}
-RTM_EXPORT(ttyname);
-
-unsigned int sleep(unsigned int seconds)
-{
-    if (rt_thread_self() != RT_NULL)
-    {
-        rt_thread_delay(seconds * RT_TICK_PER_SECOND);
-    }
-    else /* scheduler has not run yet */
-    {
-        while(seconds > 0)
-        {
-            rt_hw_us_delay(1000000u);
-            seconds --;
-        }
-    }
-
-    return 0;
-}
-RTM_EXPORT(sleep);
-
-int usleep(useconds_t usec)
-{
-    if (rt_thread_self() != RT_NULL)
-    {
-        rt_thread_mdelay(usec / 1000u);
-    }
-    else  /* scheduler has not run yet */
-    {
-        rt_hw_us_delay(usec / 1000u);
-    }
-    rt_hw_us_delay(usec % 1000u);
-
-    return 0;
-}
-RTM_EXPORT(usleep);
-
-pid_t gettid(void)
-{
-    /*TODO*/
-    return 0;
-}
-
-pid_t getpid(void)
-{
-    return gettid();
-}
-RTM_EXPORT(getpid);
-
-pid_t getppid(void)
-{
-    return 0;
-}
-RTM_EXPORT(getppid);
-
-uid_t getuid(void)
-{
-    return 0; /*ROOT*/
-}
-RTM_EXPORT(getuid);
-
-uid_t geteuid(void)
-{
-    return 0; /*ROOT*/
-}
-RTM_EXPORT(geteuid);
-
-gid_t getgid(void)
-{
-    return 0; /*ROOT*/
-}
-RTM_EXPORT(getgid);
-
-gid_t getegid(void)
-{
-    return 0; /*ROOT*/
-}
-RTM_EXPORT(getegid);
diff --git a/components/libc/posix/aio/SConscript b/components/libc/posix/aio/SConscript
index f10462e9c438c0f30226e8fd5af58beca50cae69..445efaade53c85608646bb090bd46edbb66a5dac 100644
--- a/components/libc/posix/aio/SConscript
+++ b/components/libc/posix/aio/SConscript
@@ -3,9 +3,9 @@
 from building import *
 
 cwd     = GetCurrentDir()
-src     = Glob('*.c') + Glob('*.cpp')
+src     = Glob('*.c')
 CPPPATH = [cwd]
 
-group = DefineGroup('libc', src, depend = ['RT_USING_POSIX', 'RT_USING_POSIX_AIO'], CPPPATH = CPPPATH)
+group = DefineGroup('POSIX', src, depend = ['RT_USING_POSIX', 'RT_USING_POSIX_AIO'], CPPPATH = CPPPATH)
 
 Return('group')
diff --git a/components/libc/posix/getline/SConscript b/components/libc/posix/getline/SConscript
index fa4c8618c181e3b64c15c989c88259b45d0c4cf2..bb18dc04c525eaf6fd052d158acd53b7f4afed0b 100644
--- a/components/libc/posix/getline/SConscript
+++ b/components/libc/posix/getline/SConscript
@@ -6,7 +6,7 @@ cwd = GetCurrentDir()
 src = Glob('*.c') + Glob('*.cpp')
 CPPPATH = [cwd]
 
-group = DefineGroup('libc', src, 
+group = DefineGroup('POSIX', src,
     depend = ['RT_USING_LIBC', 'RT_USING_POSIX','RT_USING_POSIX_GETLINE'], 
     CPPPATH = CPPPATH)
 
diff --git a/components/libc/posix/mmap/SConscript b/components/libc/posix/mmap/SConscript
index 1a36a15710d552ac4052f72041279399c62ce609..fd5b2b953e83d2f2e81909bef3b76fffcf976c79 100644
--- a/components/libc/posix/mmap/SConscript
+++ b/components/libc/posix/mmap/SConscript
@@ -6,7 +6,7 @@ cwd = GetCurrentDir()
 src = Glob('*.c') + Glob('*.cpp')
 CPPPATH = [cwd]
 
-group = DefineGroup('libc', src, 
+group = DefineGroup('POSIX', src,
     depend = ['RT_USING_DFS', 'RT_USING_POSIX_MMAP'],
     CPPPATH = CPPPATH)
 
diff --git a/components/libc/posix/pthreads/SConscript b/components/libc/posix/pthreads/SConscript
index 767b406d4c7b1fa361525e99842cf8cd60c7cb07..7cd78300b2a5d0a43fcc2284fe40b8952eb2fee1 100644
--- a/components/libc/posix/pthreads/SConscript
+++ b/components/libc/posix/pthreads/SConscript
@@ -16,7 +16,7 @@ try:
 except :
     pass
 
-group = DefineGroup('libc', src, 
+group = DefineGroup('POSIX', src, 
     depend = ['RT_USING_PTHREADS', 'RT_USING_LIBC'], CPPPATH = CPPPATH, CPPDEFINES = CPPDEFINES)
 
 Return('group')
diff --git a/components/libc/posix/signal/SConscript b/components/libc/posix/signal/SConscript
index f07ff58f6e5f737f2e00541ff5ec0df20ea3ebc1..07cd98cbe02810a3159fa409b916b611ed2bc9cb 100644
--- a/components/libc/posix/signal/SConscript
+++ b/components/libc/posix/signal/SConscript
@@ -6,7 +6,7 @@ cwd = GetCurrentDir()
 src = Glob('*.c') + Glob('*.cpp')
 CPPPATH = [cwd]
 
-group = DefineGroup('libc', src, 
+group = DefineGroup('POSIX', src, 
     depend = ['RT_USING_SIGNALS', 'RT_USING_PTHREADS', 'RT_USING_LIBC'], 
     CPPPATH = CPPPATH)
 
diff --git a/components/libc/posix/src/SConscript b/components/libc/posix/src/SConscript
new file mode 100644
index 0000000000000000000000000000000000000000..5640181ac52908e831fdaefa9144c4ebabc47231
--- /dev/null
+++ b/components/libc/posix/src/SConscript
@@ -0,0 +1,10 @@
+# RT-Thread building script for component
+
+from building import *
+
+cwd     = GetCurrentDir()
+src     = Glob('*.c')
+
+group = DefineGroup('POSIX', src, depend = ['RT_USING_POSIX'])
+
+Return('group')
diff --git a/components/libc/compilers/common/delay.c b/components/libc/posix/src/delay.c
similarity index 75%
rename from components/libc/compilers/common/delay.c
rename to components/libc/posix/src/delay.c
index 4666258d3b56dab6c150b5d878e36dfac863d6f2..1638caafbf51c1edbe455b8772378ace1b671be3 100644
--- a/components/libc/compilers/common/delay.c
+++ b/components/libc/posix/src/delay.c
@@ -9,6 +9,15 @@
  */
 #include <rtthread.h>
 #include <rthw.h>
+#define DBG_TAG    "POSIX.delay"
+#define DBG_LVL    DBG_INFO
+#include <rtdbg.h>
+
+RT_WEAK void rt_hw_us_delay(rt_uint32_t us)
+{
+    (void) us;
+    LOG_W("Please consider implementing rt_hw_us_delay() in another file.");
+}
 
 void msleep(unsigned int msecs)
 {
diff --git a/components/dfs/src/dfs_poll.c b/components/libc/posix/src/poll.c
similarity index 98%
rename from components/dfs/src/dfs_poll.c
rename to components/libc/posix/src/poll.c
index 607b3487befc0a796ad0aac2f89771b44da2af5f..2109fb310bff6d831c4213c8ce724825e7b485a9 100644
--- a/components/dfs/src/dfs_poll.c
+++ b/components/libc/posix/src/poll.c
@@ -9,14 +9,9 @@
  * 2018-03-09     Bernard      Add protection for pt->triggered.
  */
 #include <stdint.h>
-
 #include <rthw.h>
-#include <rtdevice.h>
 #include <rtthread.h>
-
-#include <dfs.h>
 #include <dfs_file.h>
-#include <dfs_posix.h>
 #include <poll.h>
 
 #ifdef RT_USING_POSIX
diff --git a/components/dfs/src/dfs_select.c b/components/libc/posix/src/select.c
similarity index 98%
rename from components/dfs/src/dfs_select.c
rename to components/libc/posix/src/select.c
index 795b816354f0e75e059c536df04186af617ecbe4..25cda0f0d138ea466826da1b503c6707d9aac354 100644
--- a/components/dfs/src/dfs_select.c
+++ b/components/libc/posix/src/select.c
@@ -7,10 +7,7 @@
  * Date           Author       Notes
  * 2016-12-28     Bernard      first version
  */
-#include <dfs.h>
-#include <dfs_fs.h>
-#include <dfs_posix.h>
-
+#include <rtthread.h>
 #include <poll.h>
 #include <sys/select.h>
 
diff --git a/components/dfs/src/dfs_posix.c b/components/libc/posix/src/unistd.c
similarity index 91%
rename from components/dfs/src/dfs_posix.c
rename to components/libc/posix/src/unistd.c
index acc05fcd53ec551befce0449a63ab40873d72c5e..ef2df2c2feb0ca97dd4157c1f8ed8047660fd497 100644
--- a/components/dfs/src/dfs_posix.c
+++ b/components/libc/posix/src/unistd.c
@@ -5,19 +5,15 @@
  *
  * Change Logs:
  * Date           Author       Notes
- * 2009-05-27     Yi.qiu       The first version
- * 2018-02-07     Bernard      Change the 3rd parameter of open/fcntl/ioctl to '...'
+ * 2020-09-01     Meco Man     first Version
+ * 2021-02-12     Meco Man     move all functions located in <pthread_sleep.c> to this file
  */
-
-#include <dfs.h>
-#include <dfs_posix.h>
-#include "dfs_private.h"
-
-/**
- * @addtogroup FsPosixApi
- */
-
-/*@{*/
+#include <rtthread.h>
+#include <dfs_file.h>
+#include <dfs_private.h>
+#include <sys/errno.h>
+#include <unistd.h>
+#include <delay.h>
 
 /**
  * this function is a POSIX compliant version, which will open a file and
@@ -585,11 +581,6 @@ int mkdir(const char *path, mode_t mode)
 }
 RTM_EXPORT(mkdir);
 
-#ifdef RT_USING_FINSH
-#include <finsh.h>
-FINSH_FUNCTION_EXPORT(mkdir, create a directory);
-#endif
-
 /**
  * this function is a POSIX compliant version, which will remove a directory.
  *
@@ -947,4 +938,107 @@ char *getcwd(char *buf, size_t size)
 }
 RTM_EXPORT(getcwd);
 
-/* @} */
+#ifdef RT_USING_POSIX_TERMIOS
+#include "termios.h"
+int isatty(int fd)
+{
+    struct termios ts;
+    return(tcgetattr(fd, &ts) != -1); /*true if no error (is a tty)*/
+}
+#else
+int isatty(int fd)
+{
+    if (fd >=0 && fd < 3)
+    {
+        return 1;
+    }
+    else
+    {
+        return 0;
+    }
+}
+#endif
+RTM_EXPORT(isatty);
+
+char *ttyname(int fd)
+{
+    return "/dev/tty"; /* TODO: need to add more specific */
+}
+RTM_EXPORT(ttyname);
+
+unsigned int sleep(unsigned int seconds)
+{
+    if (rt_thread_self() != RT_NULL)
+    {
+        ssleep(seconds);
+    }
+    else /* scheduler has not run yet */
+    {
+        while(seconds > 0)
+        {
+            udelay(1000000u);
+            seconds --;
+        }
+    }
+
+    return 0;
+}
+RTM_EXPORT(sleep);
+
+int usleep(useconds_t usec)
+{
+    if (rt_thread_self() != RT_NULL)
+    {
+        msleep(usec / 1000u);
+    }
+    else  /* scheduler has not run yet */
+    {
+        udelay(usec / 1000u);
+    }
+    udelay(usec % 1000u);
+
+    return 0;
+}
+RTM_EXPORT(usleep);
+
+pid_t gettid(void)
+{
+    /*TODO*/
+    return 0;
+}
+
+pid_t getpid(void)
+{
+    return gettid();
+}
+RTM_EXPORT(getpid);
+
+pid_t getppid(void)
+{
+    return 0;
+}
+RTM_EXPORT(getppid);
+
+uid_t getuid(void)
+{
+    return 0; /*ROOT*/
+}
+RTM_EXPORT(getuid);
+
+uid_t geteuid(void)
+{
+    return 0; /*ROOT*/
+}
+RTM_EXPORT(geteuid);
+
+gid_t getgid(void)
+{
+    return 0; /*ROOT*/
+}
+RTM_EXPORT(getgid);
+
+gid_t getegid(void)
+{
+    return 0; /*ROOT*/
+}
+RTM_EXPORT(getegid);
diff --git a/components/libc/posix/termios/SConscript b/components/libc/posix/termios/SConscript
index 381eb5ad8bba4e86e55f5800e6ed258dadaf9348..bd9a5284613bb413a899db209990e5e32e078c2d 100644
--- a/components/libc/posix/termios/SConscript
+++ b/components/libc/posix/termios/SConscript
@@ -6,7 +6,7 @@ cwd = GetCurrentDir()
 src = Glob('*.c') + Glob('*.cpp')
 CPPPATH = [cwd]
 
-group = DefineGroup('libc', src, 
+group = DefineGroup('POSIX', src, 
     depend = ['RT_USING_LIBC', 'RT_USING_POSIX', 'RT_USING_POSIX_TERMIOS'], 
     CPPPATH = CPPPATH)
 
diff --git a/include/rtdebug.h b/include/rtdebug.h
index 8c7d450ad4e6762b441e20a8acc2f996ad275e80..c170d148c10d25e1cdfc712ba08d8cd0f8121178 100644
--- a/include/rtdebug.h
+++ b/include/rtdebug.h
@@ -17,18 +17,7 @@
 #if !defined(RT_USING_DFS) || !defined(RT_USING_DFS_DEVFS)
 #error "POSIX poll/select, stdin need file system(RT_USING_DFS) and device file system(RT_USING_DFS_DEVFS)"
 #endif
-
-#if !defined(RT_USING_LIBC)
-#error "POSIX layer need standard C library(RT_USING_LIBC)"
-#endif
-
-#endif
-
-#ifdef RT_USING_POSIX_TERMIOS
-#if !defined(RT_USING_POSIX)
-#error "termios need POSIX layer(RT_USING_POSIX)"
-#endif
-#endif
+#endif /* RT_USING_POSIX */
 
 /* Using this macro to control all kernel debug features. */
 #ifdef RT_DEBUG