Change all time conversions. Yech. New timer units in microseconds breaks all existing logic that used milliseconds in the conversions. Something likely got broken doing this, probably because I confused a MSEC2TICK conversion with a TICK2MSEC conversion. Also, the tickless OS no appears fully functional and passes the OS test on the simulator with no errors

52 files changed, 121 insertions, 116 deletions

diff --git a/apps/examples/ostest/ostest_main.c b/apps/examples/ostest/ostest_main.c
index a234e50e6..f7879ed3a 100644
--- a/apps/examples/ostest/ostest_main.c
+++ b/apps/examples/ostest/ostest_main.c
@@ -322,7 +322,7 @@ static int user_main(int argc, char *argv[])
 #endif
 
 #ifdef  CONFIG_ARCH_FPU
-  /* Check that the FPU is properly supported during context switching */
+      /* Check that the FPU is properly supported during context switching */
 
       printf("\nuser_main: FPU test\n");
       fpu_test();
diff --git a/apps/examples/ostest/restart.c b/apps/examples/ostest/restart.c
index 2193c8108..0d0f90d07 100644
--- a/apps/examples/ostest/restart.c
+++ b/apps/examples/ostest/restart.c
@@ -189,5 +189,5 @@ void restart_test(void)
       sleep(1);
     }
 
-  printf("restart_main: Exitting\n");
+  printf("restart_main: Exiting\n");
 }
diff --git a/nuttx/arch/8051/src/up_unblocktask.c b/nuttx/arch/8051/src/up_unblocktask.c
index d285ddbd2..cb4e65fc0 100644
--- a/nuttx/arch/8051/src/up_unblocktask.c
+++ b/nuttx/arch/8051/src/up_unblocktask.c
@@ -100,7 +100,7 @@ void up_unblock_task(FAR struct tcb_s *tcb)
    */
 
 #if CONFIG_RR_INTERVAL > 0
-  tcb->timeslice = CONFIG_RR_INTERVAL / MSEC_PER_TICK;
+  tcb->timeslice = MSEC2TICK(CONFIG_RR_INTERVAL);
 #endif
 
   /* Add the task in the correct location in the prioritized
diff --git a/nuttx/arch/arm/src/arm/up_unblocktask.c b/nuttx/arch/arm/src/arm/up_unblocktask.c
index 64536d959..3476441b4 100644
--- a/nuttx/arch/arm/src/arm/up_unblocktask.c
+++ b/nuttx/arch/arm/src/arm/up_unblocktask.c
@@ -97,7 +97,7 @@ void up_unblock_task(struct tcb_s *tcb)
    */
 
 #if CONFIG_RR_INTERVAL > 0
-  tcb->timeslice = CONFIG_RR_INTERVAL / MSEC_PER_TICK;
+  tcb->timeslice = MSEC2TICK(CONFIG_RR_INTERVAL);
 #endif
 
   /* Add the task in the correct location in the prioritized
diff --git a/nuttx/arch/arm/src/armv6-m/up_unblocktask.c b/nuttx/arch/arm/src/armv6-m/up_unblocktask.c
index 0d51d21ca..7a76a24d8 100644
--- a/nuttx/arch/arm/src/armv6-m/up_unblocktask.c
+++ b/nuttx/arch/arm/src/armv6-m/up_unblocktask.c
@@ -96,7 +96,7 @@ void up_unblock_task(struct tcb_s *tcb)
    */
 
 #if CONFIG_RR_INTERVAL > 0
-  tcb->timeslice = CONFIG_RR_INTERVAL / MSEC_PER_TICK;
+  tcb->timeslice = MSEC2TICK(CONFIG_RR_INTERVAL);
 #endif
 
   /* Add the task in the correct location in the prioritized
diff --git a/nuttx/arch/arm/src/armv7-a/arm_unblocktask.c b/nuttx/arch/arm/src/armv7-a/arm_unblocktask.c
index f08ceeca3..c5ca09092 100644
--- a/nuttx/arch/arm/src/armv7-a/arm_unblocktask.c
+++ b/nuttx/arch/arm/src/armv7-a/arm_unblocktask.c
@@ -97,7 +97,7 @@ void up_unblock_task(struct tcb_s *tcb)
    */
 
 #if CONFIG_RR_INTERVAL > 0
-  tcb->timeslice = CONFIG_RR_INTERVAL / MSEC_PER_TICK;
+  tcb->timeslice = MSEC2TICK(CONFIG_RR_INTERVAL);
 #endif
 
   /* Add the task in the correct location in the prioritized
diff --git a/nuttx/arch/arm/src/armv7-m/up_unblocktask.c b/nuttx/arch/arm/src/armv7-m/up_unblocktask.c
index 551e5b67b..f2455e594 100644
--- a/nuttx/arch/arm/src/armv7-m/up_unblocktask.c
+++ b/nuttx/arch/arm/src/armv7-m/up_unblocktask.c
@@ -97,7 +97,7 @@ void up_unblock_task(struct tcb_s *tcb)
    */
 
 #if CONFIG_RR_INTERVAL > 0
-  tcb->timeslice = CONFIG_RR_INTERVAL / MSEC_PER_TICK;
+  tcb->timeslice = MSEC2TICK(CONFIG_RR_INTERVAL);
 #endif
 
   /* Add the task in the correct location in the prioritized
diff --git a/nuttx/arch/arm/src/c5471/c5471_timerisr.c b/nuttx/arch/arm/src/c5471/c5471_timerisr.c
index 1021fb84a..fc1143162 100644
--- a/nuttx/arch/arm/src/c5471/c5471_timerisr.c
+++ b/nuttx/arch/arm/src/c5471/c5471_timerisr.c
@@ -53,7 +53,7 @@
  ************************************************************/
 
 /* We want the general purpose timer running at the rate
- * MSEC_PER_TICK. The C5471 clock is 47.5MHz and we're using
+ * USEC_PER_TICK. The C5471 clock is 47.5MHz and we're using
  * a timer PTV value of 3 (3 == divide incoming frequency by
  * 16) which then yields a 16 bitCLKS_PER_INT value
  * of 29687.
@@ -114,7 +114,7 @@ void up_timer_initialize(void)
   up_disable_irq(C5471_IRQ_SYSTIMER);
 
   /* Start the general purpose timer running in auto-reload mode
-   * so that an interrupt is generated at the rate MSEC_PER_TICK.
+   * so that an interrupt is generated at the rate USEC_PER_TICK.
    */
 
   val = ((CLKS_PER_INT-1) << CLKS_PER_INT_SHIFT) | AR | ST | PTV;
diff --git a/nuttx/arch/arm/src/dm320/dm320_timerisr.c b/nuttx/arch/arm/src/dm320/dm320_timerisr.c
index a92478aa3..fae340714 100644
--- a/nuttx/arch/arm/src/dm320/dm320_timerisr.c
+++ b/nuttx/arch/arm/src/dm320/dm320_timerisr.c
@@ -139,7 +139,7 @@ void up_timer_initialize(void)
   up_disable_irq(DM320_IRQ_SYSTIMER);
 
   /* Start timer0 running so that an interrupt is generated at
-   * the rate MSEC_PER_TICK.
+   * the rate USEC_PER_TICK.
    */
 
   putreg16(DM320_TMR0_PRSCL, DM320_TIMER0_TMPRSCL); /* Timer 0 Prescalar */
diff --git a/nuttx/arch/arm/src/imx/imx_timerisr.c b/nuttx/arch/arm/src/imx/imx_timerisr.c
index 64db2e06d..d21b804c6 100644
--- a/nuttx/arch/arm/src/imx/imx_timerisr.c
+++ b/nuttx/arch/arm/src/imx/imx_timerisr.c
@@ -138,11 +138,11 @@ void up_timer_initialize(void)
    * putreg(0, IMX_TIMER1_TPRER); -- already the case
    *
    * Set the compare register so that the COMP interrupt is generated
-   * with a period of MSEC_PER_TICK.  The value IMX_PERCLK1_FREQ/1000
+   * with a period of USEC_PER_TICK.  The value IMX_PERCLK1_FREQ/1000
    * (defined in board.h) is the number of counts in millisecond, so:
    */
 
-   putreg32((IMX_PERCLK1_FREQ / 1000) * MSEC_PER_TICK, IMX_TIMER1_TCMP);
+   putreg32(MSEC2TICK(IMX_PERCLK1_FREQ / 1000), IMX_TIMER1_TCMP);
 
   /* Configure to provide timer COMP interrupts when TCN increments
    * to TCMP.
diff --git a/nuttx/arch/arm/src/kinetis/kinetis_sdhc.c b/nuttx/arch/arm/src/kinetis/kinetis_sdhc.c
index 3ba8c4299..6ff5092e5 100644
--- a/nuttx/arch/arm/src/kinetis/kinetis_sdhc.c
+++ b/nuttx/arch/arm/src/kinetis/kinetis_sdhc.c
@@ -2409,7 +2409,7 @@ static sdio_eventset_t kinetis_eventwait(FAR struct sdio_dev_s *dev,
 
       /* Start the watchdog timer */
 
-      delay = (timeout + (MSEC_PER_TICK-1)) / MSEC_PER_TICK;
+      delay = MSEC2TICK(timeout);
       ret   = wd_start(priv->waitwdog, delay, (wdentry_t)kinetis_eventtimeout,
                        1, (uint32_t)priv);
       if (ret != OK)
diff --git a/nuttx/arch/arm/src/lpc17xx/lpc17_sdcard.c b/nuttx/arch/arm/src/lpc17xx/lpc17_sdcard.c
index 0fd719f24..d5b143118 100644
--- a/nuttx/arch/arm/src/lpc17xx/lpc17_sdcard.c
+++ b/nuttx/arch/arm/src/lpc17xx/lpc17_sdcard.c
@@ -2266,7 +2266,7 @@ static sdio_eventset_t lpc17_eventwait(FAR struct sdio_dev_s *dev,
 
       /* Start the watchdog timer */
 
-      delay = (timeout + (MSEC_PER_TICK-1)) / MSEC_PER_TICK;
+      delay = MSEC2TICK(timeout);
       ret   = wd_start(priv->waitwdog, delay, (wdentry_t)lpc17_eventtimeout,
                        1, (uint32_t)priv);
       if (ret != OK)
diff --git a/nuttx/arch/arm/src/sam34/sam_hsmci.c b/nuttx/arch/arm/src/sam34/sam_hsmci.c
index 94d052bd1..d770b2d2b 100644
--- a/nuttx/arch/arm/src/sam34/sam_hsmci.c
+++ b/nuttx/arch/arm/src/sam34/sam_hsmci.c
@@ -2273,7 +2273,7 @@ static sdio_eventset_t sam_eventwait(FAR struct sdio_dev_s *dev,
 
       /* Start the watchdog timer */
 
-      delay = (timeout + (MSEC_PER_TICK-1)) / MSEC_PER_TICK;
+      delay = MSEC2TICK(timeout);
       ret   = wd_start(priv->waitwdog, delay, (wdentry_t)sam_eventtimeout,
                        1, (uint32_t)priv);
       if (ret != OK)
diff --git a/nuttx/arch/arm/src/sam34/sam_spi.c b/nuttx/arch/arm/src/sam34/sam_spi.c
index 5e32faf69..81c73a76f 100644
--- a/nuttx/arch/arm/src/sam34/sam_spi.c
+++ b/nuttx/arch/arm/src/sam34/sam_spi.c
@@ -127,7 +127,7 @@
  */
 
 #define DMA_TIMEOUT_MS    (800)
-#define DMA_TIMEOUT_TICKS ((DMA_TIMEOUT_MS + (MSEC_PER_TICK-1)) / MSEC_PER_TICK)
+#define DMA_TIMEOUT_TICKS MSEC2TICK(DMA_TIMEOUT_MS)
 
 /* Debug *******************************************************************/
 /* Check if SPI debut is enabled (non-standard.. no support in
diff --git a/nuttx/arch/arm/src/sama5/sam_hsmci.c b/nuttx/arch/arm/src/sama5/sam_hsmci.c
index f0a0d3be1..670c3a69f 100644
--- a/nuttx/arch/arm/src/sama5/sam_hsmci.c
+++ b/nuttx/arch/arm/src/sama5/sam_hsmci.c
@@ -2737,7 +2737,7 @@ static sdio_eventset_t sam_eventwait(FAR struct sdio_dev_s *dev,
           timeout = MAX(5000, timeout);
         }
 
-      delay = (timeout + (MSEC_PER_TICK-1)) / MSEC_PER_TICK;
+      delay = MSEC2TICK(timeout);
       ret   = wd_start(priv->waitwdog, delay, (wdentry_t)sam_eventtimeout,
                        1, (uint32_t)priv);
       if (ret != OK)
diff --git a/nuttx/arch/arm/src/sama5/sam_spi.c b/nuttx/arch/arm/src/sama5/sam_spi.c
index 104691077..3a1a4652a 100644
--- a/nuttx/arch/arm/src/sama5/sam_spi.c
+++ b/nuttx/arch/arm/src/sama5/sam_spi.c
@@ -120,7 +120,7 @@
  */
 
 #define DMA_TIMEOUT_MS    (800)
-#define DMA_TIMEOUT_TICKS ((DMA_TIMEOUT_MS + (MSEC_PER_TICK-1)) / MSEC_PER_TICK)
+#define DMA_TIMEOUT_TICKS MSEC2TICK(DMA_TIMEOUT_MS)
 
 /* Debug *******************************************************************/
 /* Check if SPI debut is enabled (non-standard.. no support in
diff --git a/nuttx/arch/arm/src/sama5/sam_ssc.c b/nuttx/arch/arm/src/sama5/sam_ssc.c
index 475cf06b2..570b85078 100644
--- a/nuttx/arch/arm/src/sama5/sam_ssc.c
+++ b/nuttx/arch/arm/src/sama5/sam_ssc.c
@@ -390,7 +390,7 @@
  */
 
 #define DMA_TIMEOUT_MS    (800)
-#define DMA_TIMEOUT_TICKS ((DMA_TIMEOUT_MS + (MSEC_PER_TICK-1)) / MSEC_PER_TICK)
+#define DMA_TIMEOUT_TICKS MSEC2TICK(DMA_TIMEOUT_MS)
 
 /* Debug *******************************************************************/
 /* Check if SSC debut is enabled (non-standard.. no support in
diff --git a/nuttx/arch/arm/src/sama5/sam_tsd.c b/nuttx/arch/arm/src/sama5/sam_tsd.c
index c3d45307f..fe73afc3d 100644
--- a/nuttx/arch/arm/src/sama5/sam_tsd.c
+++ b/nuttx/arch/arm/src/sama5/sam_tsd.c
@@ -89,7 +89,7 @@
 
 /* Poll the pen position while the pen is down at this rate (50MS): */
 
-#define TSD_WDOG_DELAY      ((50 + (MSEC_PER_TICK-1))/ MSEC_PER_TICK)
+#define TSD_WDOG_DELAY      MSEC2TICK(50)
 
 /* This is a value for the threshold that guantees a big difference on the
  * first pendown (but can't overflow).
diff --git a/nuttx/arch/arm/src/sama5/sam_twi.c b/nuttx/arch/arm/src/sama5/sam_twi.c
index 2e1c6a1a9..eec19f6e6 100644
--- a/nuttx/arch/arm/src/sama5/sam_twi.c
+++ b/nuttx/arch/arm/src/sama5/sam_twi.c
@@ -527,7 +527,7 @@ static int twi_wait(struct twi_dev_s *priv, unsigned int size)
    * There is no concern about arithmetic overflow for reasonable transfer sizes.
    */
 
-  timeout = (TWI_TIMEOUT_MSPB * size) / MSEC_PER_TICK;
+  timeout = MSEC2TICK(TWI_TIMEOUT_MSPB);
   if (timeout < 1)
     {
       timeout = 1;
diff --git a/nuttx/arch/arm/src/stm32/stm32_otgfshost.c b/nuttx/arch/arm/src/stm32/stm32_otgfshost.c
index 7866365d9..7fe99c1c3 100644
--- a/nuttx/arch/arm/src/stm32/stm32_otgfshost.c
+++ b/nuttx/arch/arm/src/stm32/stm32_otgfshost.c
@@ -151,8 +151,8 @@
 
 #define STM32_READY_DELAY         200000 /* In loop counts */
 #define STM32_FLUSH_DELAY         200000 /* In loop counts */
-#define STM32_SETUP_DELAY         (5000 / MSEC_PER_TICK) /* 5 seconds in system ticks */
-#define STM32_DATANAK_DELAY       (5000 / MSEC_PER_TICK) /* 5 seconds in system ticks */
+#define STM32_SETUP_DELAY         SEC2TICK(5) /* 5 seconds in system ticks */
+#define STM32_DATANAK_DELAY       SEC2TICK(5) /* 5 seconds in system ticks */
 
 /* Ever-present MIN/MAX macros */
 
diff --git a/nuttx/arch/arm/src/stm32/stm32_sdio.c b/nuttx/arch/arm/src/stm32/stm32_sdio.c
index f731ad75c..cc164bc80 100644
--- a/nuttx/arch/arm/src/stm32/stm32_sdio.c
+++ b/nuttx/arch/arm/src/stm32/stm32_sdio.c
@@ -2315,7 +2315,7 @@ static sdio_eventset_t stm32_eventwait(FAR struct sdio_dev_s *dev,
 
       /* Start the watchdog timer */
 
-      delay = (timeout + (MSEC_PER_TICK-1)) / MSEC_PER_TICK;
+      delay = MSEC2TICK(timeout);
       ret   = wd_start(priv->waitwdog, delay, (wdentry_t)stm32_eventtimeout,
                        1, (uint32_t)priv);
       if (ret != OK)
diff --git a/nuttx/arch/avr/src/avr/up_unblocktask.c b/nuttx/arch/avr/src/avr/up_unblocktask.c
index 305e057a8..6fb2e67e5 100644
--- a/nuttx/arch/avr/src/avr/up_unblocktask.c
+++ b/nuttx/arch/avr/src/avr/up_unblocktask.c
@@ -97,7 +97,7 @@ void up_unblock_task(struct tcb_s *tcb)
    */
 
 #if CONFIG_RR_INTERVAL > 0
-  tcb->timeslice = CONFIG_RR_INTERVAL / MSEC_PER_TICK;
+  tcb->timeslice = MSEC2TICK(CONFIG_RR_INTERVAL);
 #endif
 
   /* Add the task in the correct location in the prioritized
diff --git a/nuttx/arch/avr/src/avr32/up_unblocktask.c b/nuttx/arch/avr/src/avr32/up_unblocktask.c
index 42dc3d52a..f53550da9 100644
--- a/nuttx/arch/avr/src/avr32/up_unblocktask.c
+++ b/nuttx/arch/avr/src/avr32/up_unblocktask.c
@@ -97,7 +97,7 @@ void up_unblock_task(struct tcb_s *tcb)
    */
 
 #if CONFIG_RR_INTERVAL > 0
-  tcb->timeslice = CONFIG_RR_INTERVAL / MSEC_PER_TICK;
+  tcb->timeslice = MSEC2TICK(CONFIG_RR_INTERVAL);
 #endif
 
   /* Add the task in the correct location in the prioritized
diff --git a/nuttx/arch/hc/src/common/up_unblocktask.c b/nuttx/arch/hc/src/common/up_unblocktask.c
index 08cefc1d4..425db0f98 100644
--- a/nuttx/arch/hc/src/common/up_unblocktask.c
+++ b/nuttx/arch/hc/src/common/up_unblocktask.c
@@ -97,7 +97,7 @@ void up_unblock_task(struct tcb_s *tcb)
    */
 
 #if CONFIG_RR_INTERVAL > 0
-  tcb->timeslice = CONFIG_RR_INTERVAL / MSEC_PER_TICK;
+  tcb->timeslice = MSEC2TICK(CONFIG_RR_INTERVAL);
 #endif
 
   /* Add the task in the correct location in the prioritized
diff --git a/nuttx/arch/mips/src/mips32/up_unblocktask.c b/nuttx/arch/mips/src/mips32/up_unblocktask.c
index 277ec79cf..dab958b15 100644
--- a/nuttx/arch/mips/src/mips32/up_unblocktask.c
+++ b/nuttx/arch/mips/src/mips32/up_unblocktask.c
@@ -99,7 +99,7 @@ void up_unblock_task(struct tcb_s *tcb)
    */
 
 #if CONFIG_RR_INTERVAL > 0
-  tcb->timeslice = CONFIG_RR_INTERVAL / MSEC_PER_TICK;
+  tcb->timeslice = MSEC2TICK(CONFIG_RR_INTERVAL);
 #endif
 
   /* Add the task in the correct location in the prioritized
diff --git a/nuttx/arch/rgmp/src/nuttx.c b/nuttx/arch/rgmp/src/nuttx.c
index e6fee5de1..0178ae58a 100644
--- a/nuttx/arch/rgmp/src/nuttx.c
+++ b/nuttx/arch/rgmp/src/nuttx.c
@@ -326,7 +326,7 @@ void up_unblock_task(struct tcb_s *tcb)
          * robin tasks but it doesn't here to do it for everything
          */
 #if CONFIG_RR_INTERVAL > 0
-        tcb->timeslice = CONFIG_RR_INTERVAL / MSEC_PER_TICK;
+        tcb->timeslice = MSEC2TICK(CONFIG_RR_INTERVAL);
 #endif
 
         // Add the task in the correct location in the prioritized
diff --git a/nuttx/arch/sh/src/common/up_unblocktask.c b/nuttx/arch/sh/src/common/up_unblocktask.c
index 5ba0173fb..a4b598499 100644
--- a/nuttx/arch/sh/src/common/up_unblocktask.c
+++ b/nuttx/arch/sh/src/common/up_unblocktask.c
@@ -97,7 +97,7 @@ void up_unblock_task(struct tcb_s *tcb)
    */
 
 #if CONFIG_RR_INTERVAL > 0
-  tcb->timeslice = CONFIG_RR_INTERVAL / MSEC_PER_TICK;
+  tcb->timeslice = MSEC2TICK(CONFIG_RR_INTERVAL);
 #endif
 
   /* Add the task in the correct location in the prioritized
diff --git a/nuttx/arch/sim/src/up_tickless.c b/nuttx/arch/sim/src/up_tickless.c
index 57a793534..4e04cd71e 100644
--- a/nuttx/arch/sim/src/up_tickless.c
+++ b/nuttx/arch/sim/src/up_tickless.c
@@ -66,6 +66,7 @@
 #include <time.h>
 
 #include <nuttx/arch.h>
+#include <nuttx/clock.h>
 
 #ifdef CONFIG_SCHED_TICKLESS
 
@@ -74,12 +75,12 @@
  ****************************************************************************/
 
 #if defined(CONFIG_SIM_WALLTIME) || defined(CONFIG_SIM_X11FB)
-#  define TICK_USEC (1000000 / CLK_TCK)
-#  define TICK_SEC  (TICK_USEC / 1000000)
-#  define TICK_NSEC ((TICK_USEC % 1000) * 1000)
+#  define TICK_USEC (USEC_PER_SEC / CLK_TCK)
+#  define TICK_SEC  (TICK_USEC / USEC_PER_SEC)
+#  define TICK_NSEC ((TICK_USEC % NSEC_PER_USEC) * NSEC_PER_USEC)
 #else
-#  define TICK_SEC 0
-#  define TICK_NSEC (128 * 1000)
+#  define TICK_SEC  0
+#  define TICK_NSEC NSEC_PER_TICK
 #endif
 
 /****************************************************************************
@@ -209,8 +210,8 @@ int up_timer_cancel(FAR struct timespec *ts)
 
   if (g_timer_active)
     {
-      ts->tv_sec  = g_interval_delay.tv_nsec;
-      ts->tv_nsec = g_interval_delay.tv_sec;
+      ts->tv_sec  = g_interval_delay.tv_sec;
+      ts->tv_nsec = g_interval_delay.tv_nsec;
     }
   else
     {
@@ -220,8 +221,8 @@ int up_timer_cancel(FAR struct timespec *ts)
 
   /* Disable and reset the simulated timer */
 
-  g_interval_delay.tv_nsec = 0;
   g_interval_delay.tv_sec  = 0;
+  g_interval_delay.tv_nsec = 0;
   g_timer_active           = false;
 }
 #endif
@@ -253,8 +254,8 @@ int up_timer_cancel(FAR struct timespec *ts)
 #ifdef CONFIG_SCHED_TICKLESS
 int up_timer_start(FAR const struct timespec *ts)
 {
-  g_interval_delay.tv_nsec = ts->tv_nsec;
   g_interval_delay.tv_sec  = ts->tv_sec;
+  g_interval_delay.tv_nsec = ts->tv_nsec;
   g_timer_active           = true;
 }
 #endif
@@ -278,10 +279,10 @@ void up_timer_update(void)
   /* Increment the elapsed time */
 
   g_elapsed_time.tv_nsec += TICK_NSEC;
-  if (g_elapsed_time.tv_nsec >= 1000000000)
+  if (g_elapsed_time.tv_nsec >= NSEC_PER_SEC)
     {
-      g_elapsed_time.tv_nsec++;
-      g_elapsed_time.tv_sec -= 1000000000;
+      g_elapsed_time.tv_sec++;
+      g_elapsed_time.tv_nsec -= NSEC_PER_SEC;
     }
 
   g_elapsed_time.tv_sec += TICK_SEC;
@@ -307,7 +308,7 @@ void up_timer_update(void)
 
           /* Decrement nanoseconds */
 
-          if (g_interval_delay.tv_nsec > TICK_NSEC)
+          if (g_interval_delay.tv_nsec >= TICK_NSEC)
             {
               g_interval_delay.tv_nsec -= TICK_NSEC;
             }
@@ -316,14 +317,10 @@ void up_timer_update(void)
 
           else if (g_interval_delay.tv_sec > 0)
             {
-              if (g_interval_delay.tv_nsec >= TICK_NSEC)
-                {
-                  g_interval_delay.tv_nsec = 0;
-                }
-              else
-                {
-                  g_interval_delay.tv_sec--;
-                }
+              g_interval_delay.tv_nsec += NSEC_PER_SEC;
+              g_interval_delay.tv_sec--;
+
+              g_interval_delay.tv_nsec -= TICK_NSEC;
             }
 
           /* Otherwise the timer has expired */
diff --git a/nuttx/arch/sim/src/up_unblocktask.c b/nuttx/arch/sim/src/up_unblocktask.c
index 04c2349e4..2da05edcc 100644
--- a/nuttx/arch/sim/src/up_unblocktask.c
+++ b/nuttx/arch/sim/src/up_unblocktask.c
@@ -99,7 +99,7 @@ void up_unblock_task(struct tcb_s *tcb)
    */
 
 #if CONFIG_RR_INTERVAL > 0
-  tcb->timeslice = CONFIG_RR_INTERVAL / MSEC_PER_TICK;
+  tcb->timeslice = MSEC2TICK(CONFIG_RR_INTERVAL);
 #endif
 
   /* Add the task in the correct location in the prioritized
diff --git a/nuttx/arch/x86/src/common/up_unblocktask.c b/nuttx/arch/x86/src/common/up_unblocktask.c
index 43b93c4e6..9e5597f16 100644
--- a/nuttx/arch/x86/src/common/up_unblocktask.c
+++ b/nuttx/arch/x86/src/common/up_unblocktask.c
@@ -96,7 +96,7 @@ void up_unblock_task(struct tcb_s *tcb)
    */
 
 #if CONFIG_RR_INTERVAL > 0
-  tcb->timeslice = CONFIG_RR_INTERVAL / MSEC_PER_TICK;
+  tcb->timeslice = MSEC2TICK(CONFIG_RR_INTERVAL);
 #endif
 
   /* Add the task in the correct location in the prioritized
diff --git a/nuttx/arch/z16/src/common/up_unblocktask.c b/nuttx/arch/z16/src/common/up_unblocktask.c
index 984e514ad..28bb95417 100644
--- a/nuttx/arch/z16/src/common/up_unblocktask.c
+++ b/nuttx/arch/z16/src/common/up_unblocktask.c
@@ -101,7 +101,7 @@ void up_unblock_task(FAR struct tcb_s *tcb)
    */
 
 #if CONFIG_RR_INTERVAL > 0
-  tcb->timeslice = CONFIG_RR_INTERVAL / MSEC_PER_TICK;
+  tcb->timeslice = MSEC2TICK(CONFIG_RR_INTERVAL);
 #endif
 
   /* Add the task in the correct location in the prioritized
diff --git a/nuttx/arch/z80/src/common/up_unblocktask.c b/nuttx/arch/z80/src/common/up_unblocktask.c
index 6c46b0a14..bc829db0d 100644
--- a/nuttx/arch/z80/src/common/up_unblocktask.c
+++ b/nuttx/arch/z80/src/common/up_unblocktask.c
@@ -102,7 +102,7 @@ void up_unblock_task(FAR struct tcb_s *tcb)
    */
 
 #if CONFIG_RR_INTERVAL > 0
-  tcb->timeslice = CONFIG_RR_INTERVAL / MSEC_PER_TICK;
+  tcb->timeslice = MSEC2TICK(CONFIG_RR_INTERVAL);
 #endif
 
   /* Add the task in the correct location in the prioritized
diff --git a/nuttx/configs/mikroe-stm32f4/src/up_touchscreen.c b/nuttx/configs/mikroe-stm32f4/src/up_touchscreen.c
index 095168c89..52edd65de 100644
--- a/nuttx/configs/mikroe-stm32f4/src/up_touchscreen.c
+++ b/nuttx/configs/mikroe-stm32f4/src/up_touchscreen.c
@@ -156,11 +156,11 @@
 /* Delays ***************************************************************************/
 /* All values will be increased by one system timer tick (probably 10MS). */
 
-#define TC_PENUP_POLL_TICKS   (70 / MSEC_PER_TICK) /* IDLE polling rate: 100 MSec */
-#define TC_PENDOWN_POLL_TICKS (40 / MSEC_PER_TICK) /* Active polling rate: 60 MSec */
-#define TC_DEBOUNCE_TICKS     (16 / MSEC_PER_TICK) /* Delay before re-sampling: 30 MSec */
-#define TC_SAMPLE_TICKS       (4 / MSEC_PER_TICK)  /* Delay for A/D sampling: 4 MSec */
-#define TC_SETTLE_TICKS       (10 / MSEC_PER_TICK) /* Delay for A/D settling: 4 MSec */
+#define TC_PENUP_POLL_TICKS   MSEC2TICK(70)  /* IDLE polling rate: 70 MSec */
+#define TC_PENDOWN_POLL_TICKS MSEC2TICK(40)  /* Active polling rate: 40 MSec */
+#define TC_DEBOUNCE_TICKS     MSEC2TICK(16)  /* Delay before re-sampling: 16 MSec */
+#define TC_SAMPLE_TICKS       MSEC2TICK(4)   /* Delay for A/D sampling: 4 MSec */
+#define TC_SETTLE_TICKS       MSECT2TICK(10) /* Delay for A/D settling: 10 MSec */
 #define TC_RESAMPLE_TICKS     TC_SAMPLE_TICKS
 
 /************************************************************************************
diff --git a/nuttx/configs/pic32mx7mmb/src/up_touchscreen.c b/nuttx/configs/pic32mx7mmb/src/up_touchscreen.c
index d29111f67..99b35151c 100644
--- a/nuttx/configs/pic32mx7mmb/src/up_touchscreen.c
+++ b/nuttx/configs/pic32mx7mmb/src/up_touchscreen.c
@@ -142,10 +142,10 @@
 /* Delays ***************************************************************************/
 /* All values will be increased by one system timer tick (probably 10MS). */
 
-#define TC_PENUP_POLL_TICKS   (100 / MSEC_PER_TICK) /* IDLE polling rate: 100 MSec */
-#define TC_PENDOWN_POLL_TICKS (60 / MSEC_PER_TICK)  /* Active polling rate: 60 MSec */
-#define TC_DEBOUNCE_TICKS     (30 / MSEC_PER_TICK)  /* Delay before re-sampling: 30 MSec */
-#define TC_SAMPLE_TICKS       (4 / MSEC_PER_TICK)   /* Delay for A/D sampling: 4 MSec */
+#define TC_PENUP_POLL_TICKS   MSEC2TICK(100) /* IDLE polling rate: 100 MSec */
+#define TC_PENDOWN_POLL_TICKS MSEC2TICK(60)  /* Active polling rate: 60 MSec */
+#define TC_DEBOUNCE_TICKS     MSEC2TICK(30)  /* Delay before re-sampling: 30 MSec */
+#define TC_SAMPLE_TICKS       MSEC2TICK(4)   /* Delay for A/D sampling: 4 MSec */
 #define TC_RESAMPLE_TICKS     TC_SAMPLE_TICKS
 
 /************************************************************************************
diff --git a/nuttx/configs/sam4s-xplained-pro/src/sam_tc.c b/nuttx/configs/sam4s-xplained-pro/src/sam_tc.c
index 4012bb80d..bad80cc3e 100755
--- a/nuttx/configs/sam4s-xplained-pro/src/sam_tc.c
+++ b/nuttx/configs/sam4s-xplained-pro/src/sam_tc.c
@@ -218,8 +218,8 @@ int sam_timerinitialize(void)
 
   /* Set the timeout */
 
-  tcvdbg("Interval = %d us.\n",  (unsigned long)MSEC_PER_TICK * 1000);
-  ret = ioctl(fd, TCIOC_SETTIMEOUT, (unsigned long)MSEC_PER_TICK * 1000);
+  tcvdbg("Interval = %d us.\n",  (unsigned long)USEC_PER_TICK);
+  ret = ioctl(fd, TCIOC_SETTIMEOUT, (unsigned long)USEC_PER_TICK);
   if (ret < 0)
     {
       tcdbg("ioctl(TCIOC_SETTIMEOUT) failed: %d\n", errno);
diff --git a/nuttx/drivers/audio/wm8904.c b/nuttx/drivers/audio/wm8904.c
index 0d7a79c87..707f5fd28 100644
--- a/nuttx/drivers/audio/wm8904.c
+++ b/nuttx/drivers/audio/wm8904.c
@@ -1475,6 +1475,9 @@ static int wm8904_sendbuffer(FAR struct wm8904_dev_s *priv)
        * REVISIT:  Does this take into account the number channels?  Perhaps
        * saving an reusing the bitrate would give a better and simpler
        * calculation.
+       *
+       * REVISIT:  Should not use MSEC_PER_TICK.  It can be inaccurate with
+       * microsecond resolution timer.
        */
 
       timeout = (((uint32_t)(apb->nbytes - apb->curbyte) << 14) /
diff --git a/nuttx/drivers/input/ads7843e.h b/nuttx/drivers/input/ads7843e.h
index d3c82816f..97c45d042 100644
--- a/nuttx/drivers/input/ads7843e.h
+++ b/nuttx/drivers/input/ads7843e.h
@@ -100,7 +100,7 @@
 
 /* Poll the pen position while the pen is down at this rate (50MS): */
 
-#define ADS7843E_WDOG_DELAY  ((50 + (MSEC_PER_TICK-1))/ MSEC_PER_TICK)
+#define ADS7843E_WDOG_DELAY       MSEC2TICK(50)
 
 /********************************************************************************************
  * Public Types
diff --git a/nuttx/drivers/input/max11802.h b/nuttx/drivers/input/max11802.h
index 075631799..8a6da0468 100644
--- a/nuttx/drivers/input/max11802.h
+++ b/nuttx/drivers/input/max11802.h
@@ -90,7 +90,7 @@
 
 /* Poll the pen position while the pen is down at this rate (50MS): */
 
-#define MAX11802_WDOG_DELAY  ((50 + (MSEC_PER_TICK-1))/ MSEC_PER_TICK)
+#define MAX11802_WDOG_DELAY     MSEC2TICK(50)
 
 /********************************************************************************************
  * Public Types
diff --git a/nuttx/drivers/input/stmpe811.h b/nuttx/drivers/input/stmpe811.h
index f6d646527..fb686ee44 100644
--- a/nuttx/drivers/input/stmpe811.h
+++ b/nuttx/drivers/input/stmpe811.h
@@ -96,7 +96,7 @@
 
 /* Timeout to detect missing pen up events */
 
-#define STMPE811_PENUP_TICKS  ((100 + (MSEC_PER_TICK-1)) / MSEC_PER_TICK)
+#define STMPE811_PENUP_TICKS            MSEC2TICK(100)
 
 /********************************************************************************************
  * Public Types
diff --git a/nuttx/drivers/mtd/sst39vf.c b/nuttx/drivers/mtd/sst39vf.c
index b404a9435..e2fe862c9 100644
--- a/nuttx/drivers/mtd/sst39vf.c
+++ b/nuttx/drivers/mtd/sst39vf.c
@@ -435,7 +435,7 @@ static int sst39vf_chiperase(FAR struct sst39vf_dev_s *priv)
   wrinfo.data    = 0xffff;
 
   start = clock_systimer();
-  while (delay < SST39VF_TSCE_MSEC * MSEC_PER_TICK)
+  while (delay < MSEC2TICK(SST39VF_TSCE_MSEC))
     {
       /* Check if the erase is complete */
 
@@ -447,14 +447,14 @@ static int sst39vf_chiperase(FAR struct sst39vf_dev_s *priv)
       /* No, check if the timeout has elapsed */
 
       elapsed = clock_systimer() - start;
-      if (elapsed > SST39VF_TSCE_MSEC * MSEC_PER_TICK)
+      if (elapsed > MSEC2TICK(SST39VF_TSCE_MSEC))
         {
           return -ETIMEDOUT;
         }
 
       /* No, wait one system clock tick */
 
-      usleep(MSEC_PER_TICK * USEC_PER_MSEC);
+      usleep(USEC_PER_TICK);
     }
 #else
   /* Delay the maximum amount of time for the chip erase to complete. */
@@ -511,7 +511,7 @@ static int sst39vf_sectorerase(FAR struct sst39vf_dev_s *priv,
 
 #if 0
   start = clock_systimer();
-  while (delay < SST39VF_TSE_MSEC * MSEC_PER_TICK)
+  while (delay < MSEC2TICK(SST39VF_TSE_MSEC))
     {
       /* Check if the erase is complete */
 
@@ -523,14 +523,14 @@ static int sst39vf_sectorerase(FAR struct sst39vf_dev_s *priv,
       /* No, check if the timeout has elapsed */
 
       elapsed = clock_systimer() - start;
-      if (elapsed > SST39VF_TSE_MSEC * MSEC_PER_TICK)
+      if (elapsed > MSEC2TICK(SST39VF_TSE_MSEC))
         {
           return -ETIMEDOUT;
         }
 
       /* No, wait one system clock tick */
 
-      usleep(MSEC_PER_TICK * USEC_PER_MSEC);
+      usleep(USEC_PER_TICK);
     }
 #else
   /* Delay the maximum amount of time for the sector erase to complete. */
diff --git a/nuttx/include/nuttx/clock.h b/nuttx/include/nuttx/clock.h
index 509d624d2..fcd8c5c58 100644
--- a/nuttx/include/nuttx/clock.h
+++ b/nuttx/include/nuttx/clock.h
@@ -115,13 +115,12 @@
 
 #define TICK_PER_DSEC         (USEC_PER_DSEC / USEC_PER_TICK)            /* Truncates! */
 #define TICK_PER_SEC          (USEC_PER_SEC / USEC_PER_TICK)             /* Truncates! */
-#define MSEC_PER_TICK         (USEC_PER_MSEC / USEC_PER_TICK)            /* Truncates! */
+#define TICK_PER_MSEC         (USEC_PER_MSEC / USEC_PER_TICK)            /* Truncates! */
+#define MSEC_PER_TICK         (USEC_PER_TICK / USEC_PER_MSEC)            /* Truncates! */
 #define NSEC_PER_TICK         (USEC_PER_TICK * NSEC_PER_USEC)            /* Exact */
 
 #define NSEC2TICK(nsec)       (((nsec)+(NSEC_PER_TICK/2))/NSEC_PER_TICK) /* Rounds */
 #define USEC2TICK(usec)       (((usec)+(USEC_PER_TICK/2))/USEC_PER_TICK) /* Rounds */
-#define DSEC2TICK(dsec)       MSEC2TICK((dsec)*MSEC_PER_DSEC)            /* Exact */
-#define SEC2TICK(sec)         MSEC2TICK((sec)*MSEC_PER_SEC)              /* Exact */
 
 #if (MSEC_PER_TICK * USEC_PER_MSEC) == USEC_PER_TICK
 #  define MSEC2TICK(msec)     (((msec)+(MSEC_PER_TICK/2))/MSEC_PER_TICK) /* Rounds */
@@ -129,10 +128,11 @@
 #  define MSEC2TICK(msec)     USEC2TICK(msec * 1000)                     /* Rounds */
 #endif
 
+#define DSEC2TICK(dsec)       MSEC2TICK((dsec)*MSEC_PER_DSEC)            /* Exact */
+#define SEC2TICK(sec)         MSEC2TICK((sec)*MSEC_PER_SEC)              /* Exact */
+
 #define TICK2NSEC(tick)       ((tick)*NSEC_PER_TICK)                     /* Exact */
 #define TICK2USEC(tick)       ((tick)*USEC_PER_TICK)                     /* Exact */
-#define TICK2DSEC(tick)       (((tick)+(TICK_PER_DSEC/2))/TICK_PER_DSEC) /* Rounds */
-#define TICK2SEC(tick)        (((tick)+(TICK_PER_SEC/2))/TICK_PER_SEC)   /* Rounds */
 
 #if (MSEC_PER_TICK * USEC_PER_MSEC) == USEC_PER_TICK
 #define TICK2USEC(tick)       ((tick)*MSEC_PER_TICK)                     /* Exact */
@@ -140,6 +140,9 @@
 #  define TICK2MSEC(tick)     (((tick)*USEC_PER_TICK)/USEC_PER_MSEC)     /* Rounds */
 #endif
 
+#define TICK2DSEC(tick)       (((tick)+(TICK_PER_DSEC/2))/TICK_PER_DSEC) /* Rounds */
+#define TICK2SEC(tick)        (((tick)+(TICK_PER_SEC/2))/TICK_PER_SEC)   /* Rounds */
+
 /****************************************************************************
  * Public Types
  ****************************************************************************/
diff --git a/nuttx/sched/Kconfig b/nuttx/sched/Kconfig
index 7568e6f25..4f7a88bd3 100644
--- a/nuttx/sched/Kconfig
+++ b/nuttx/sched/Kconfig
@@ -93,6 +93,9 @@ config USEC_PER_TICK
 		The default, 100 microseconds, will provide for a range of delays
 		up to 120 hours.
 
+		This value should never be less than the underlying resolution of
+		the timer.  Error may ensue.
+
 if !SCHED_TICKLESS
 
 config SYSTEMTICK_EXTCLK
diff --git a/nuttx/sched/clock_getres.c b/nuttx/sched/clock_getres.c
index a76b14ab6..edbc87bf0 100644
--- a/nuttx/sched/clock_getres.c
+++ b/nuttx/sched/clock_getres.c
@@ -88,7 +88,6 @@
 
 int clock_getres(clockid_t clock_id, struct timespec *res)
 {
-  uint32_t time_res;
   int      ret = OK;
 
   sdbg("clock_id=%d\n", clock_id);
@@ -103,18 +102,12 @@ int clock_getres(clockid_t clock_id, struct timespec *res)
     }
   else
     {
-      /* Get the clock resolution in nanoseconds */
-
-      time_res = MSEC_PER_TICK * NSEC_PER_MSEC;
-
-      /* And return this as a timespec. */
+      /* Form the timspec using clock resolution in nanoseconds */
 
       res->tv_sec  = 0;
-      res->tv_nsec = time_res;
+      res->tv_nsec = NSEC_PER_TICK;
 
-      sdbg("Returning res=(%d,%d) time_res=%d\n",
-           (int)res->tv_sec, (int)res->tv_nsec,
-           (int)time_res);
+      sdbg("Returning res=(%d,%d)\n", (int)res->tv_sec, (int)res->tv_nsec);
     }
 
   return ret;
diff --git a/nuttx/sched/clock_gettime.c b/nuttx/sched/clock_gettime.c
index 7f6cdba62..5244bc531 100644
--- a/nuttx/sched/clock_gettime.c
+++ b/nuttx/sched/clock_gettime.c
@@ -124,7 +124,7 @@ int clock_gettime(clockid_t clock_id, struct timespec *tp)
     {
       /* Get the time since power-on in seconds and milliseconds */
 
-      msecs = MSEC_PER_TICK * clock_systimer();
+      msecs = TICK2MSEC(clock_systimer());
       secs  = msecs / MSEC_PER_SEC;
 
       /* Return the elapsed time in seconds and nanoseconds */
@@ -174,7 +174,7 @@ int clock_gettime(clockid_t clock_id, struct timespec *tp)
            * when the time-of-day was last set.
            */
 
-          msecs = MSEC_PER_TICK * (clock_systimer() - g_tickbias);
+          msecs = TICK2MSEC((clock_systimer() - g_tickbias));
 
           sdbg("msecs = %d g_tickbias=%d\n",
                (int)msecs, (int)g_tickbias);
diff --git a/nuttx/sched/clock_initialize.c b/nuttx/sched/clock_initialize.c
index 0b21fd56a..374e675ac 100644
--- a/nuttx/sched/clock_initialize.c
+++ b/nuttx/sched/clock_initialize.c
@@ -266,7 +266,7 @@ void clock_synchronize(void)
  * Description:
  *   This function must be called once every time the real time clock
  *   interrupt occurs.  The interval of this clock interrupt must be
- *   MSEC_PER_TICK
+ *   USEC_PER_TICK
  *
  ****************************************************************************/
 
@@ -277,4 +277,4 @@ void clock_timer(void)
 
   g_system_timer++;
 }
-#endif
\ No newline at end of file
+#endif
diff --git a/nuttx/sched/clock_systimer.c b/nuttx/sched/clock_systimer.c
index 126c12ce6..65487da6e 100644
--- a/nuttx/sched/clock_systimer.c
+++ b/nuttx/sched/clock_systimer.c
@@ -87,8 +87,7 @@ uint32_t clock_systimer(void)
 
   /* Convert to a 64- then 32-bit value */
 
-  tmp = (1000 * (uint64_t)ts.tv_sec + (uint64_t)ts.tv_nsec / 1000000) /
-        MSEC_PER_TICK;
+  tmp = MSEC2TICK(1000 * (uint64_t)ts.tv_sec + (uint64_t)ts.tv_nsec / 1000000);
   return (uint32_t)(tmp & 0x00000000ffffffff);
 
 #else
@@ -136,8 +135,7 @@ uint64_t clock_systimer64(void)
 
   /* Convert to a 64- then 32-bit value */
 
-  return (1000 * (uint64_t)ts.tv_sec + (uint64_t)ts.tv_nsec / 1000000) /
-         MSEC_PER_TICK;
+  return MSEC2TICK(1000 * (uint64_t)ts.tv_sec + (uint64_t)ts.tv_nsec / 1000000);
 
 #else
   /* Return the current system time */
diff --git a/nuttx/sched/pthread_create.c b/nuttx/sched/pthread_create.c
index 8c9292cfc..78142a6ed 100644
--- a/nuttx/sched/pthread_create.c
+++ b/nuttx/sched/pthread_create.c
@@ -381,7 +381,7 @@ int pthread_create(FAR pthread_t *thread, FAR pthread_attr_t *attr,
   if (policy == SCHED_RR)
     {
       ptcb->cmn.flags    |= TCB_FLAG_ROUND_ROBIN;
-      ptcb->cmn.timeslice = CONFIG_RR_INTERVAL / MSEC_PER_TICK;
+      ptcb->cmn.timeslice = MSEC2TICK(CONFIG_RR_INTERVAL);
     }
 #endif
 
diff --git a/nuttx/sched/sched_processtimer.c b/nuttx/sched/sched_processtimer.c
index e16d17e71..a8a3b917f 100644
--- a/nuttx/sched/sched_processtimer.c
+++ b/nuttx/sched/sched_processtimer.c
@@ -115,7 +115,7 @@ static inline void sched_process_timeslice(void)
             {
               /* Reset the timeslice in any case. */
 
-              rtcb->timeslice = CONFIG_RR_INTERVAL / MSEC_PER_TICK;
+              rtcb->timeslice = MSEC2TICK(CONFIG_RR_INTERVAL);
 
               /* We know we are at the head of the ready to run
                * prioritized list.  We must be the highest priority
@@ -170,7 +170,7 @@ static inline void sched_process_timeslice(void)
  *   The timer interrupt logic itself is implemented in the
  *   architecture specific code, but must call the following OS
  *   function periodically -- the calling interval must be
- *   MSEC_PER_TICK
+ *   USEC_PER_TICK
  *
  * Inputs:
  *   None
diff --git a/nuttx/sched/sched_setscheduler.c b/nuttx/sched/sched_setscheduler.c
index 682f50530..cabf81bec 100644
--- a/nuttx/sched/sched_setscheduler.c
+++ b/nuttx/sched/sched_setscheduler.c
@@ -157,7 +157,7 @@ int sched_setscheduler(pid_t pid, int policy,
       /* Set round robin scheduling */
 
       tcb->flags    |= TCB_FLAG_ROUND_ROBIN;
-      tcb->timeslice = CONFIG_RR_INTERVAL / MSEC_PER_TICK;
+      tcb->timeslice = MSEC2TICK(CONFIG_RR_INTERVAL);
     }
   else
     {
diff --git a/nuttx/sched/sched_timerexpiration.c b/nuttx/sched/sched_timerexpiration.c
index 7f2a5b863..03cdfceef 100644
--- a/nuttx/sched/sched_timerexpiration.c
+++ b/nuttx/sched/sched_timerexpiration.c
@@ -171,7 +171,7 @@ sched_process_timeslice(unsigned int ticks, bool noswitches)
             {
               /* Reset the timeslice. */
 
-              rtcb->timeslice = CONFIG_RR_INTERVAL / MSEC_PER_TICK;
+              rtcb->timeslice = MSEC2TICK(CONFIG_RR_INTERVAL);
               ret = rtcb->timeslice;
 
               /* We know we are at the head of the ready to run
@@ -287,7 +287,7 @@ static void sched_timer_process(unsigned int ticks, bool noswitches)
        * understand.
        */
 
-      msecs = MSEC_PER_TICK * nextime;
+      msecs = TICK2MSEC(nextime);
       secs  = msecs / MSEC_PER_SEC;
       nsecs = (msecs - (secs * MSEC_PER_SEC)) * NSEC_PER_MSEC;
 
@@ -327,7 +327,11 @@ static void sched_timer_process(unsigned int ticks, bool noswitches)
 
 void sched_timer_expiration(void)
 {
-  sched_timer_process(g_timer_interval, false);
+  unsigned int elapsed;
+
+  elapsed          = g_timer_interval;
+  g_timer_interval = 0;
+  sched_timer_process(elapsed, false);
 }
 
 /****************************************************************************
@@ -358,6 +362,7 @@ void sched_timer_reassess(void)
 {
   struct timespec ts;
   unsigned int ticks;
+  unsigned int elapsed;
 
   /* Get the time remaining on the interval timer and cancel the timer. */
 
@@ -367,13 +372,16 @@ void sched_timer_reassess(void)
 
   ticks  = SEC2TICK(ts.tv_sec);
   ticks += NSEC2TICK(ts.tv_nsec);
+  DEBUGASSERT(ticks <= g_timer_interval);
 
   /* Handle the partial timer.  This will reassess all timer conditions and
    * re-start the interval timer with the correct delay.  Context switches
    * are not permitted in this case because we are not certain of the
    * calling conditions.
    */
-  
-  sched_timer_process(g_timer_interval - ticks, true);
+
+  elapsed          = g_timer_interval - ticks;
+  g_timer_interval = 0;
+  sched_timer_process(elapsed, true);
 }
 #endif /* CONFIG_SCHED_TICKLESS */
diff --git a/nuttx/sched/sched_unlock.c b/nuttx/sched/sched_unlock.c
index 91aa555ef..df3b966e7 100644
--- a/nuttx/sched/sched_unlock.c
+++ b/nuttx/sched/sched_unlock.c
@@ -45,7 +45,7 @@
 #include "os_internal.h"
 
 /************************************************************************
- * Definitions
+ * Pre-processor Definitions
  ************************************************************************/
 
 /************************************************************************
@@ -65,7 +65,7 @@
  ************************************************************************/
 
 /************************************************************************
- * Private Functionss
+ * Private Functions
  ************************************************************************/
 
 /************************************************************************
@@ -125,11 +125,11 @@ int sched_unlock(void)
             }
 
 #if CONFIG_RR_INTERVAL > 0
-          /* If (1) the task that was running running supported round-robin
-           * scheduling and (2) if its time slice has already expired, but (3)
-           * it could not slice out because pre-emption was disabled, then
-           * we need to swap the task out now and reassess the interval timer
-           * for the next time slice.
+          /* If (1) the task that was running supported round-robin
+           * scheduling and (2) if its time slice has already expired, but
+           * (3) it could not slice out because pre-emption was disabled,
+           * then we need to swap the task out now and reassess the interval
+           * timer for the next time slice.
            */
 
           if ((rtcb->flags & TCB_FLAG_ROUND_ROBIN) != 0 &&
@@ -144,7 +144,7 @@ int sched_unlock(void)
 
               if (rtcb != (FAR struct tcb_s*)g_readytorun.head)
                 {
-                  rtcb->timeslice = CONFIG_RR_INTERVAL / MSEC_PER_TICK;
+                  rtcb->timeslice = MSEC2TICK(CONFIG_RR_INTERVAL);
                 }
 #ifdef CONFIG_SCHED_TICKLESS
               else
diff --git a/nuttx/sched/sig_timedwait.c b/nuttx/sched/sig_timedwait.c
index 3952e42c2..85b870642 100644
--- a/nuttx/sched/sig_timedwait.c
+++ b/nuttx/sched/sig_timedwait.c
@@ -254,7 +254,7 @@ int sigtimedwait(FAR const sigset_t *set, FAR struct siginfo *info,
           DEBUGASSERT(timeout->tv_sec < UINT32_MAX / MSEC_PER_SEC);
           waitmsec = timeout->tv_sec * MSEC_PER_SEC +
                     (timeout->tv_nsec + NSEC_PER_MSEC - 1) / NSEC_PER_MSEC;
-          waitticks = (waitmsec + MSEC_PER_TICK - 1) / MSEC_PER_TICK;
+          waitticks = MSEC2TICK(waitmsec);
 #endif
 
           /* Create a watchdog */