diff --git a/boards/arm/cxd56xx/common/src/cxd56_audio.c b/boards/arm/cxd56xx/common/src/cxd56_audio.c
index 8c695734350..8d0cbe8555d 100644
--- a/boards/arm/cxd56xx/common/src/cxd56_audio.c
+++ b/boards/arm/cxd56xx/common/src/cxd56_audio.c
@@ -47,6 +47,7 @@
 #include <debug.h>
 
 #include <nuttx/arch.h>
+#include <nuttx/signal.h>
 #include <arch/chip/audio.h>
 
 #include "chip.h"
@@ -297,13 +298,13 @@ int board_external_amp_mute_control(bool en)
       /* Mute ON */
 
       ret = board_power_control(POWER_AUDIO_MUTE, false);
-      usleep(MUTE_ON_DELAY);
+      nxsig_usleep(MUTE_ON_DELAY);
     }
   else
     {
       /* Mute OFF */
 
-      usleep(MUTE_OFF_DELAY);
+      nxsig_usleep(MUTE_OFF_DELAY);
       ret = board_power_control(POWER_AUDIO_MUTE, true);
     }
 
diff --git a/boards/arm/cxd56xx/common/src/cxd56_isx012.c b/boards/arm/cxd56xx/common/src/cxd56_isx012.c
index 6faefc08220..9f49870a408 100644
--- a/boards/arm/cxd56xx/common/src/cxd56_isx012.c
+++ b/boards/arm/cxd56xx/common/src/cxd56_isx012.c
@@ -43,12 +43,14 @@
 #include <debug.h>
 #include <errno.h>
 
+#include <nuttx/arch.h>
+#include <nuttx/board.h>
+#include <nuttx/signal.h>
+
 #include "cxd56_gpio.h"
 #include "cxd56_pinconfig.h"
 #include "cxd56_i2c.h"
 
-#include <nuttx/arch.h>
-#include <nuttx/board.h>
 #include <arch/board/board.h>
 
 /****************************************************************************
@@ -111,8 +113,9 @@ int board_isx012_power_on(void)
           break;
         }
 
-      usleep(POWER_CHECK_TIME);
+      nxsig_usleep(POWER_CHECK_TIME);
     }
+
   return ret;
 }
 
@@ -144,7 +147,7 @@ int board_isx012_power_off(void)
           break;
         }
 
-      usleep(POWER_CHECK_TIME);
+      nxsig_usleep(POWER_CHECK_TIME);
     }
 
   return ret;
@@ -167,20 +170,20 @@ void board_isx012_set_sleep(int kind)
     {
       /* PowerON -> sleep */
 
-      usleep(DEVICE_STARTUP_TIME);
+      nxsig_usleep(DEVICE_STARTUP_TIME);
     }
   else
     {
       /* active -> sleep */
 
-      usleep(STANDBY_TIME);
+      nxsig_usleep(STANDBY_TIME);
     }
 }
 
 void board_isx012_release_sleep(void)
 {
   cxd56_gpio_write(IMAGER_SLEEP, true);
-  usleep(SLEEP_CANCEL_TIME);
+  nxsig_usleep(SLEEP_CANCEL_TIME);
 }
 
 int isx012_register(FAR struct i2c_master_s *i2c);
diff --git a/boards/arm/cxd56xx/drivers/audio/cxd56_audio_analog.c b/boards/arm/cxd56xx/drivers/audio/cxd56_audio_analog.c
index 16e7b9695dd..4a6558ed7a4 100644
--- a/boards/arm/cxd56xx/drivers/audio/cxd56_audio_analog.c
+++ b/boards/arm/cxd56xx/drivers/audio/cxd56_audio_analog.c
@@ -38,9 +38,13 @@
  ****************************************************************************/
 
 #include <nuttx/config.h>
+
+#include <time.h>
+
 #include <nuttx/arch.h>
 #include <nuttx/irq.h>
-#include <time.h>
+#include <nuttx/signal.h>
+
 #include <arch/board/board.h>
 #include <arch/chip/audio.h>
 
@@ -107,7 +111,7 @@ static void wait_mic_boot_finish(void)
 
       if (time < CXD56_AUDIO_MIC_BOOT_WAIT)
         {
-          usleep((CXD56_AUDIO_MIC_BOOT_WAIT - time) * 1000);
+          nxsig_usleep((CXD56_AUDIO_MIC_BOOT_WAIT - time) * 1000);
         }
     }
 }
diff --git a/boards/arm/cxd56xx/drivers/audio/cxd56_audio_volume.c b/boards/arm/cxd56xx/drivers/audio/cxd56_audio_volume.c
index 9490a70a71b..bcb244ea45e 100644
--- a/boards/arm/cxd56xx/drivers/audio/cxd56_audio_volume.c
+++ b/boards/arm/cxd56xx/drivers/audio/cxd56_audio_volume.c
@@ -37,9 +37,11 @@
  * Included Files
  ****************************************************************************/
 
-#include <nuttx/arch.h>
 #include <nuttx/config.h>
 
+#include <nuttx/arch.h>
+#include <nuttx/signal.h>
+
 #include "cxd56_audio_config.h"
 #include "cxd56_audio_ac_reg.h"
 #include "cxd56_audio_analog.h"
@@ -134,7 +136,7 @@ static CXD56_AUDIO_ECODE set_mute(cxd56_audio_volid_t id,
 
   if (wait)
     {
-      usleep(waittime);
+      nxsig_usleep(waittime);
     }
 
   g_volparam[id].mute_bit |= type;
@@ -200,7 +202,7 @@ static CXD56_AUDIO_ECODE set_unmute(cxd56_audio_volid_t id,
 
       if (wait)
         {
-          usleep(waittime);
+          nxsig_usleep(waittime);
         }
     }
 
diff --git a/boards/arm/lc823450/lc823450-xgevk/src/lc823450_bt.c b/boards/arm/lc823450/lc823450-xgevk/src/lc823450_bt.c
index 6b9438b73d8..4109475b73d 100644
--- a/boards/arm/lc823450/lc823450-xgevk/src/lc823450_bt.c
+++ b/boards/arm/lc823450/lc823450-xgevk/src/lc823450_bt.c
@@ -39,10 +39,12 @@
 
 #include <nuttx/config.h>
 
-#include <nuttx/board.h>
-#include <arch/board/board.h>
 #include <unistd.h>
 
+#include <nuttx/board.h>
+#include <nuttx/signal.h>
+#include <arch/board/board.h>
+
 #include "chip.h"
 #include "up_arch.h"
 #include "up_internal.h"
@@ -69,9 +71,9 @@ void up_bt_enable(int enable)
   if (enable)
     {
       lc823450_gpio_write(BT_POWER, 0);
-      usleep(100 * 1000);
+      nxsig_usleep(100 * 1000);
       lc823450_gpio_write(BT_POWER, 1);
-      usleep(100 * 1000);
+      nxsig_usleep(100 * 1000);
     }
   else
     {
diff --git a/boards/arm/stm32/clicker2-stm32/src/stm32_appinit.c b/boards/arm/stm32/clicker2-stm32/src/stm32_appinit.c
index c1bf7eb3a7e..da2ef2c639b 100644
--- a/boards/arm/stm32/clicker2-stm32/src/stm32_appinit.c
+++ b/boards/arm/stm32/clicker2-stm32/src/stm32_appinit.c
@@ -1,7 +1,7 @@
 /****************************************************************************
  * boards/arm/stm32/clicker2-stm32/src/stm32_appinit.c
  *
- *   Copyright (C) 2017 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2017, 2019 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <gnutt@nuttx.org>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -44,8 +44,9 @@
 #include <unistd.h>
 #include <syslog.h>
 
-#include <nuttx/syslog/syslog.h>
 #include <nuttx/board.h>
+#include <nuttx/signal.h>
+#include <nuttx/syslog/syslog.h>
 
 #include "clicker2-stm32.h"
 
@@ -108,7 +109,7 @@ int board_app_initialize(uintptr_t arg)
    * file syslog.
    */
 
-  usleep(CONFIG_CLICKER2_STM32_SYSLOG_FILE_DELAY * 1000);
+  nxsig_usleep(CONFIG_CLICKER2_STM32_SYSLOG_FILE_DELAY * 1000);
 
   ret = syslog_file_channel(CONFIG_CLICKER2_STM32_SYSLOG_FILE_PATH);
   if (ret < 0)
diff --git a/boards/arm/stm32/nucleo-f302r8/src/stm32_highpri.c b/boards/arm/stm32/nucleo-f302r8/src/stm32_highpri.c
index 38782ffb379..c043ceb493d 100644
--- a/boards/arm/stm32/nucleo-f302r8/src/stm32_highpri.c
+++ b/boards/arm/stm32/nucleo-f302r8/src/stm32_highpri.c
@@ -1,7 +1,7 @@
 /****************************************************************************
  * boards/arm/stm32/nucleo-f302r8/src/stm32_highpri.c
  *
- *   Copyright (C) 2018 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2018, 2019 Gregory Nutt. All rights reserved.
  *   Author: Mateusz Szafoni <raiden00@railab.me>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -46,14 +46,13 @@
 
 #include <nuttx/arch.h>
 #include <nuttx/signal.h>
-
-#include <arch/irq.h>
-#include <arch/armv7-m/nvicpri.h>
-
 #include <nuttx/timers/pwm.h>
 #include <nuttx/analog/adc.h>
 #include <nuttx/analog/ioctl.h>
 
+#include <arch/irq.h>
+#include <arch/armv7-m/nvicpri.h>
+
 #include "up_internal.h"
 #include "ram_vectors.h"
 
@@ -505,7 +504,7 @@ int highpri_main(int argc, char *argv[])
 
       adc1->ad_ops->ao_ioctl(adc1, IO_TRIGGER_REG, 0);
 
-      usleep(100);
+      nxsig_usleep(100);
 #endif
 
 #ifdef HIGHPRI_HAVE_INJECTED
@@ -513,7 +512,7 @@ int highpri_main(int argc, char *argv[])
 
       adc1->ad_ops->ao_ioctl(adc1, IO_TRIGGER_INJ, 0);
 
-      usleep(100);
+      nxsig_usleep(100);
 #endif
       /* Lock global data */
 
diff --git a/boards/arm/stm32/nucleo-f334r8/src/stm32_highpri.c b/boards/arm/stm32/nucleo-f334r8/src/stm32_highpri.c
index e080682b5ed..eb8ac8b01ed 100644
--- a/boards/arm/stm32/nucleo-f334r8/src/stm32_highpri.c
+++ b/boards/arm/stm32/nucleo-f334r8/src/stm32_highpri.c
@@ -1,7 +1,7 @@
 /****************************************************************************
  * boards/arm/stm32/nucleo-f334r8/src/stm32_highpri.c
  *
- *   Copyright (C) 2018 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2018, 2019 Gregory Nutt. All rights reserved.
  *   Author: Mateusz Szafoni <raiden00@railab.me>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -46,14 +46,13 @@
 
 #include <nuttx/arch.h>
 #include <nuttx/signal.h>
-
-#include <arch/irq.h>
-#include <arch/armv7-m/nvicpri.h>
-
 #include <nuttx/timers/pwm.h>
 #include <nuttx/analog/adc.h>
 #include <nuttx/analog/ioctl.h>
 
+#include <arch/irq.h>
+#include <arch/armv7-m/nvicpri.h>
+
 #include "up_internal.h"
 #include "ram_vectors.h"
 
@@ -547,7 +546,7 @@ int highpri_main(int argc, char *argv[])
 
       adc1->ad_ops->ao_ioctl(adc1, IO_TRIGGER_REG, 0);
 
-      usleep(100);
+      nxsig_usleep(100);
 #endif
 
 #ifdef HIGHPRI_HAVE_INJECTED
@@ -555,7 +554,7 @@ int highpri_main(int argc, char *argv[])
 
       adc1->ad_ops->ao_ioctl(adc1, IO_TRIGGER_INJ, 0);
 
-      usleep(100);
+      nxsig_usleep(100);
 #endif
       /* Lock global data */
 
diff --git a/boards/arm/stm32/stm32f429i-disco/src/stm32_highpri.c b/boards/arm/stm32/stm32f429i-disco/src/stm32_highpri.c
index eb6a1371267..64f2e424714 100644
--- a/boards/arm/stm32/stm32f429i-disco/src/stm32_highpri.c
+++ b/boards/arm/stm32/stm32f429i-disco/src/stm32_highpri.c
@@ -1,7 +1,7 @@
 /****************************************************************************
  * boards/arm/stm32/stm32f429i-disco/src/stm32_highpri.c
  *
- *   Copyright (C) 2018 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2018, 2019 Gregory Nutt. All rights reserved.
  *   Author: Mateusz Szafoni <raiden00@railab.me>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -495,7 +495,7 @@ int highpri_main(int argc, char *argv[])
 
       adc1->ad_ops->ao_ioctl(adc1, IO_TRIGGER_REG, 0);
 
-      usleep(100);
+      nxsig_usleep(100);
 #endif
 
 #ifdef HIGHPRI_HAVE_INJECTED
@@ -503,7 +503,7 @@ int highpri_main(int argc, char *argv[])
 
       adc1->ad_ops->ao_ioctl(adc1, IO_TRIGGER_INJ, 0);
 
-      usleep(100);
+      nxsig_usleep(100);
 #endif
       /* Lock global data */
 
diff --git a/boards/arm/stm32f0l0g0/b-l072z-lrwan1/src/stm32_sx127x.c b/boards/arm/stm32f0l0g0/b-l072z-lrwan1/src/stm32_sx127x.c
index 52977415e33..7e104e54201 100644
--- a/boards/arm/stm32f0l0g0/b-l072z-lrwan1/src/stm32_sx127x.c
+++ b/boards/arm/stm32f0l0g0/b-l072z-lrwan1/src/stm32_sx127x.c
@@ -46,8 +46,9 @@
 #include <debug.h>
 
 #include <nuttx/board.h>
-#include <arch/board/board.h>
+#include <nuttx/signal.h>
 #include <nuttx/wireless/lpwan/sx127x.h>
+#include <arch/board/board.h>
 
 #include "stm32_gpio.h"
 #include "stm32_exti.h"
@@ -126,7 +127,7 @@ static void sx127x_chip_reset(void)
 
   /* Wait 1 ms */
 
-  usleep(1000);
+  nxsig_usleep(1000);
 
   /* Configure reset as input */
 
@@ -134,7 +135,7 @@ static void sx127x_chip_reset(void)
 
   /* Wait 10 ms */
 
-  usleep(10000);
+  nxsig_usleep(10000);
 }
 
 /****************************************************************************
diff --git a/boards/arm/stm32f0l0g0/nucleo-f091rc/src/stm32_sx127x.c b/boards/arm/stm32f0l0g0/nucleo-f091rc/src/stm32_sx127x.c
index 558a1205d34..6b08b211457 100644
--- a/boards/arm/stm32f0l0g0/nucleo-f091rc/src/stm32_sx127x.c
+++ b/boards/arm/stm32f0l0g0/nucleo-f091rc/src/stm32_sx127x.c
@@ -47,8 +47,9 @@
 #include <debug.h>
 
 #include <nuttx/board.h>
-#include <arch/board/board.h>
+#include <nuttx/signal.h>
 #include <nuttx/wireless/lpwan/sx127x.h>
+#include <arch/board/board.h>
 
 #include "stm32_gpio.h"
 #include "stm32_exti.h"
@@ -125,7 +126,7 @@ static void sx127x_chip_reset(void)
 
   /* Wait 1 ms */
 
-  usleep(1000);
+  nxsig_usleep(1000);
 
   /* Configure reset as input */
 
@@ -133,7 +134,7 @@ static void sx127x_chip_reset(void)
 
   /* Wait 10 ms */
 
-  usleep(10000);
+  nxsig_usleep(10000);
 }
 
 /****************************************************************************
diff --git a/boards/arm/stm32f0l0g0/nucleo-l073rz/src/stm32_sx127x.c b/boards/arm/stm32f0l0g0/nucleo-l073rz/src/stm32_sx127x.c
index 389f674fa77..11f0bb6bca8 100644
--- a/boards/arm/stm32f0l0g0/nucleo-l073rz/src/stm32_sx127x.c
+++ b/boards/arm/stm32f0l0g0/nucleo-l073rz/src/stm32_sx127x.c
@@ -47,8 +47,9 @@
 #include <debug.h>
 
 #include <nuttx/board.h>
-#include <arch/board/board.h>
+#include <nuttx/signal.h>
 #include <nuttx/wireless/lpwan/sx127x.h>
+#include <arch/board/board.h>
 
 #include "stm32_gpio.h"
 #include "stm32_exti.h"
@@ -125,7 +126,7 @@ static void sx127x_chip_reset(void)
 
   /* Wait 1 ms */
 
-  usleep(1000);
+  nxsig_usleep(1000);
 
   /* Configure reset as input */
 
@@ -133,7 +134,7 @@ static void sx127x_chip_reset(void)
 
   /* Wait 10 ms */
 
-  usleep(10000);
+  nxsig_usleep(10000);
 }
 
 /****************************************************************************