diff --git a/Documentation/NuttxPortingGuide.html b/Documentation/NuttxPortingGuide.html
index 808152c91a..04b746b598 100644
--- a/Documentation/NuttxPortingGuide.html
+++ b/Documentation/NuttxPortingGuide.html
@@ -12,7 +12,7 @@
       <h1><big><font color="#3c34ec">
         <i>NuttX RTOS Porting Guide</i>
       </font></big></h1>
-      <p>Last Updated: October 12, 2017</p>
+      <p>Last Updated: January 31, 2018</p>
     </td>
   </tr>
 </table>
@@ -2605,7 +2605,7 @@ pointer to a watchdog structure.
 <p>
 <b>Returned Value:</b>
 <ul>
-<li>OK or ERROR
+<li>Zero (<code>OK</code>) is returned on success; a negated <code>errno</code> value is return to indicate the nature of any failure.
 </ul>
 
 <p>
@@ -2662,7 +2662,7 @@ wd_start() on a given watchdog ID has any effect.
 <p>
 <b>Returned Value:</b>
 <ul>
-<li>OK or ERROR
+<li>Zero (<code>OK</code>) is returned on success; a negated <code>errno</code> value is return to indicate the nature of any failure.
 </ul>
 
 <p>
diff --git a/arch/arm/src/efm32/efm32_spi.c b/arch/arm/src/efm32/efm32_spi.c
index f16d196e64..d7821a553e 100644
--- a/arch/arm/src/efm32/efm32_spi.c
+++ b/arch/arm/src/efm32/efm32_spi.c
@@ -1493,7 +1493,7 @@ static void spi_exchange(struct spi_dev_s *dev, const void *txbuffer,
       ret = wd_start(priv->wdog, (int)ticks, spi_dma_timeout, 1, (uint32_t)priv);
       if (ret < 0)
         {
-          spierr("ERROR: Failed to start timeout\n");
+          spierr("ERROR: Failed to start timeout: %d\n", ret);
         }
 
       /* Then wait for each to complete.  TX should complete first */
diff --git a/arch/arm/src/kinetis/kinetis_i2c.c b/arch/arm/src/kinetis/kinetis_i2c.c
index 3e40998650..1a7af792a8 100644
--- a/arch/arm/src/kinetis/kinetis_i2c.c
+++ b/arch/arm/src/kinetis/kinetis_i2c.c
@@ -1183,8 +1183,8 @@ static int kinetis_i2c_transfer(struct i2c_master_s *dev,
 
       /* Wait for transfer complete */
 
-      wd_start(priv->timeout, I2C_TIMEOUT, kinetis_i2c_timeout, 1,
-               (uint32_t) priv);
+      (void)wd_start(priv->timeout, I2C_TIMEOUT, kinetis_i2c_timeout, 1,
+                     (uint32_t)priv);
       kinetis_i2c_wait(priv);
 
       wd_cancel(priv->timeout);
diff --git a/arch/arm/src/kinetis/kinetis_sdhc.c b/arch/arm/src/kinetis/kinetis_sdhc.c
index 1a3a0b53b7..ef59c16fe0 100644
--- a/arch/arm/src/kinetis/kinetis_sdhc.c
+++ b/arch/arm/src/kinetis/kinetis_sdhc.c
@@ -2465,7 +2465,7 @@ static sdio_eventset_t kinetis_eventwait(FAR struct sdio_dev_s *dev,
       delay = MSEC2TICK(timeout);
       ret   = wd_start(priv->waitwdog, delay, (wdentry_t)kinetis_eventtimeout,
                        1, (uint32_t)priv);
-      if (ret != OK)
+      if (ret < 0)
         {
           mcerr("ERROR: wd_start failed: %d\n", ret);
         }
diff --git a/arch/arm/src/kinetis/kinetis_usbdev.c b/arch/arm/src/kinetis/kinetis_usbdev.c
index 4d10d422fd..9fd71b3e78 100644
--- a/arch/arm/src/kinetis/kinetis_usbdev.c
+++ b/arch/arm/src/kinetis/kinetis_usbdev.c
@@ -1112,7 +1112,8 @@ static void khci_delayedrestart(struct khci_usbdev_s *priv, uint8_t epno)
 
   /* And start (or re-start) the watchdog timer */
 
-  wd_start(priv->wdog, RESTART_DELAY, khci_rqrestart, 1, (uint32_t)priv);
+  (void)wd_start(priv->wdog, RESTART_DELAY, khci_rqrestart, 1,
+                 (uint32_t)priv);
 }
 
 /****************************************************************************
diff --git a/arch/arm/src/lpc11xx/lpc11_i2c.c b/arch/arm/src/lpc11xx/lpc11_i2c.c
index 1c94939da9..5873a18ff3 100644
--- a/arch/arm/src/lpc11xx/lpc11_i2c.c
+++ b/arch/arm/src/lpc11xx/lpc11_i2c.c
@@ -215,7 +215,8 @@ static int lpc11_i2c_start(struct lpc11_i2cdev_s *priv)
            priv->base + LPC11_I2C_CONCLR_OFFSET);
   putreg32(I2C_CONSET_STA, priv->base + LPC11_I2C_CONSET_OFFSET);
 
-  wd_start(priv->timeout, I2C_TIMEOUT, lpc11_i2c_timeout, 1, (uint32_t)priv);
+  (void)wd_start(priv->timeout, I2C_TIMEOUT, lpc11_i2c_timeout, 1,
+                 (uint32_t)priv);
   nxsem_wait(&priv->wait);
 
   wd_cancel(priv->timeout);
diff --git a/arch/arm/src/lpc17xx/lpc17_i2c.c b/arch/arm/src/lpc17xx/lpc17_i2c.c
index 579e943336..522afae683 100644
--- a/arch/arm/src/lpc17xx/lpc17_i2c.c
+++ b/arch/arm/src/lpc17xx/lpc17_i2c.c
@@ -215,7 +215,8 @@ static int lpc17_i2c_start(struct lpc17_i2cdev_s *priv)
            priv->base + LPC17_I2C_CONCLR_OFFSET);
   putreg32(I2C_CONSET_STA, priv->base + LPC17_I2C_CONSET_OFFSET);
 
-  wd_start(priv->timeout, I2C_TIMEOUT, lpc17_i2c_timeout, 1, (uint32_t)priv);
+  (void)wd_start(priv->timeout, I2C_TIMEOUT, lpc17_i2c_timeout, 1,
+                 (uint32_t)priv);
   nxsem_wait(&priv->wait);
 
   wd_cancel(priv->timeout);
diff --git a/arch/arm/src/lpc17xx/lpc17_sdcard.c b/arch/arm/src/lpc17xx/lpc17_sdcard.c
index 3d7fdffe70..96cdb510f9 100644
--- a/arch/arm/src/lpc17xx/lpc17_sdcard.c
+++ b/arch/arm/src/lpc17xx/lpc17_sdcard.c
@@ -2307,7 +2307,7 @@ static sdio_eventset_t lpc17_eventwait(FAR struct sdio_dev_s *dev,
       delay = MSEC2TICK(timeout);
       ret   = wd_start(priv->waitwdog, delay, (wdentry_t)lpc17_eventtimeout,
                        1, (uint32_t)priv);
-      if (ret != OK)
+      if (ret < 0)
         {
           mcerr("ERROR: wd_start failed: %d\n", ret);
         }
diff --git a/arch/arm/src/lpc2378/lpc23xx_i2c.c b/arch/arm/src/lpc2378/lpc23xx_i2c.c
index 00d44687ea..2a99c2a084 100644
--- a/arch/arm/src/lpc2378/lpc23xx_i2c.c
+++ b/arch/arm/src/lpc2378/lpc23xx_i2c.c
@@ -220,7 +220,8 @@ static int lpc2378_i2c_start(struct lpc2378_i2cdev_s *priv)
            priv->base + I2C_CONCLR_OFFSET);
   putreg32(I2C_CONSET_STA, priv->base + I2C_CONSET_OFFSET);
 
-  wd_start(priv->timeout, I2C_TIMEOUT, lpc2378_i2c_timeout, 1, (uint32_t)priv);
+  (void)wd_start(priv->timeout, I2C_TIMEOUT, lpc2378_i2c_timeout, 1,
+                 (uint32_t)priv);
   nxsem_wait(&priv->wait);
 
   wd_cancel(priv->timeout);
diff --git a/arch/arm/src/lpc31xx/lpc31_i2c.c b/arch/arm/src/lpc31xx/lpc31_i2c.c
index c65d55c471..b4ff05cd9d 100644
--- a/arch/arm/src/lpc31xx/lpc31_i2c.c
+++ b/arch/arm/src/lpc31xx/lpc31_i2c.c
@@ -490,7 +490,7 @@ static int i2c_transfer(FAR struct i2c_master_s *dev, FAR struct i2c_msg_s *msgs
 
   /* Start a watchdog to timeout the transfer if the bus is locked up... */
 
-  wd_start(priv->timeout, I2C_TIMEOUT, i2c_timeout, 1, (uint32_t)priv);
+  (void)wd_start(priv->timeout, I2C_TIMEOUT, i2c_timeout, 1, (uint32_t)priv);
 
   /* Wait for the transfer to complete */
 
diff --git a/arch/arm/src/lpc43xx/lpc43_i2c.c b/arch/arm/src/lpc43xx/lpc43_i2c.c
index f613470a8f..64acf4f987 100644
--- a/arch/arm/src/lpc43xx/lpc43_i2c.c
+++ b/arch/arm/src/lpc43xx/lpc43_i2c.c
@@ -202,7 +202,8 @@ static int lpc43_i2c_start(struct lpc43_i2cdev_s *priv)
            priv->base + LPC43_I2C_CONCLR_OFFSET);
   putreg32(I2C_CONSET_STA, priv->base + LPC43_I2C_CONSET_OFFSET);
 
-  wd_start(priv->timeout, I2C_TIMEOUT, lpc43_i2c_timeout, 1, (uint32_t)priv);
+  (void)wd_start(priv->timeout, I2C_TIMEOUT, lpc43_i2c_timeout, 1,i
+                 (uint32_t)priv);
   nxsem_wait(&priv->wait);
 
   wd_cancel(priv->timeout);
diff --git a/arch/arm/src/lpc43xx/lpc43_sdmmc.c b/arch/arm/src/lpc43xx/lpc43_sdmmc.c
index 5d4df400b3..c3504e7a15 100644
--- a/arch/arm/src/lpc43xx/lpc43_sdmmc.c
+++ b/arch/arm/src/lpc43xx/lpc43_sdmmc.c
@@ -2262,7 +2262,7 @@ static sdio_eventset_t lpc43_eventwait(FAR struct sdio_dev_s *dev,
       delay = MSEC2TICK(timeout);
       ret   = wd_start(priv->waitwdog, delay, (wdentry_t)lpc43_eventtimeout,
                        1, (uint32_t)priv);
-      if (ret != OK)
+      if (ret < 0)
         {
           mcerr("ERROR: wd_start failed: %d\n", ret);
         }
diff --git a/arch/arm/src/lpc54xx/lpc54_i2c_master.c b/arch/arm/src/lpc54xx/lpc54_i2c_master.c
index cf4981676f..05d171a597 100644
--- a/arch/arm/src/lpc54xx/lpc54_i2c_master.c
+++ b/arch/arm/src/lpc54xx/lpc54_i2c_master.c
@@ -765,10 +765,9 @@ static int lpc54_i2c_transfer(FAR struct i2c_master_s *dev,
   priv->result = OK;
 
   /* Set up the transfer timeout */
-  /* wd_start(priv->timeout ...);  */
 
-  wd_start(priv->timeout, priv->nmsgs * I2C_WDOG_TIMEOUT, lpc54_i2c_timeout,
-           1, (uint32_t)priv);
+  (void)wd_start(priv->timeout, priv->nmsgs * I2C_WDOG_TIMEOUT,
+                 lpc54_i2c_timeout, 1, (uint32_t)priv);
 
   /* Initiate the transfer */
 
diff --git a/arch/arm/src/lpc54xx/lpc54_sdmmc.c b/arch/arm/src/lpc54xx/lpc54_sdmmc.c
index 09cb425267..626db2654f 100644
--- a/arch/arm/src/lpc54xx/lpc54_sdmmc.c
+++ b/arch/arm/src/lpc54xx/lpc54_sdmmc.c
@@ -2262,7 +2262,7 @@ static sdio_eventset_t lpc54_eventwait(FAR struct sdio_dev_s *dev,
       delay = MSEC2TICK(timeout);
       ret   = wd_start(priv->waitwdog, delay, (wdentry_t)lpc54_eventtimeout,
                        1, (uint32_t)priv);
-      if (ret != OK)
+      if (ret < 0)
         {
           mcerr("ERROR: wd_start failed: %d\n", ret);
         }
diff --git a/arch/arm/src/sam34/sam_hsmci.c b/arch/arm/src/sam34/sam_hsmci.c
index 0ac187982b..25006b7f19 100644
--- a/arch/arm/src/sam34/sam_hsmci.c
+++ b/arch/arm/src/sam34/sam_hsmci.c
@@ -2317,7 +2317,7 @@ static sdio_eventset_t sam_eventwait(FAR struct sdio_dev_s *dev,
       delay = MSEC2TICK(timeout);
       ret   = wd_start(priv->waitwdog, delay, (wdentry_t)sam_eventtimeout,
                        1, (uint32_t)priv);
-      if (ret != OK)
+      if (ret < 0)
         {
           mcerr("ERROR: wd_start failed: %d\n", ret);
         }
diff --git a/arch/arm/src/sam34/sam_spi.c b/arch/arm/src/sam34/sam_spi.c
index 0dc57e7a6c..79bc6ca9ea 100644
--- a/arch/arm/src/sam34/sam_spi.c
+++ b/arch/arm/src/sam34/sam_spi.c
@@ -1590,7 +1590,7 @@ static void spi_exchange(struct spi_dev_s *dev, const void *txbuffer,
 
       ret = wd_start(spics->dmadog, DMA_TIMEOUT_TICKS,
                      (wdentry_t)spi_dmatimeout, 1, (uint32_t)spics);
-      if (ret != OK)
+      if (ret < 0)
         {
            spierr("ERROR: wd_start failed: %d\n", ret);
         }
diff --git a/arch/arm/src/sam34/sam_twi.c b/arch/arm/src/sam34/sam_twi.c
index 18b510cbcb..7f733790f7 100644
--- a/arch/arm/src/sam34/sam_twi.c
+++ b/arch/arm/src/sam34/sam_twi.c
@@ -386,7 +386,7 @@ static int twi_wait(struct twi_dev_s *priv)
 {
   /* Start a timeout to avoid hangs */
 
-  wd_start(priv->timeout, TWI_TIMEOUT, twi_timeout, 1, (uint32_t)priv);
+  (void)wd_start(priv->timeout, TWI_TIMEOUT, twi_timeout, 1, (uint32_t)priv);
 
   /* Wait for either the TWI transfer or the timeout to complete */
 
diff --git a/arch/arm/src/sama5/sam_hsmci.c b/arch/arm/src/sama5/sam_hsmci.c
index b5093d36b0..e47248e2eb 100644
--- a/arch/arm/src/sama5/sam_hsmci.c
+++ b/arch/arm/src/sama5/sam_hsmci.c
@@ -2745,7 +2745,7 @@ static sdio_eventset_t sam_eventwait(FAR struct sdio_dev_s *dev,
       delay = MSEC2TICK(timeout);
       ret   = wd_start(priv->waitwdog, delay, (wdentry_t)sam_eventtimeout,
                        1, (uint32_t)priv);
-      if (ret != OK)
+      if (ret < 0)
         {
            lcderr("ERROR: wd_start failed: %d\n", ret);
         }
diff --git a/arch/arm/src/sama5/sam_spi.c b/arch/arm/src/sama5/sam_spi.c
index ce398400f4..457aa04f19 100644
--- a/arch/arm/src/sama5/sam_spi.c
+++ b/arch/arm/src/sama5/sam_spi.c
@@ -1520,7 +1520,7 @@ static void spi_exchange(struct spi_dev_s *dev, const void *txbuffer,
 
       ret = wd_start(spics->dmadog, DMA_TIMEOUT_TICKS,
                      (wdentry_t)spi_dmatimeout, 1, (uint32_t)spics);
-      if (ret != OK)
+      if (ret < 0)
         {
            spierr("ERROR: wd_start failed: %d\n", ret);
         }
diff --git a/arch/arm/src/sama5/sam_tsd.c b/arch/arm/src/sama5/sam_tsd.c
index 4ec8d1bf04..36fc9e6d00 100644
--- a/arch/arm/src/sama5/sam_tsd.c
+++ b/arch/arm/src/sama5/sam_tsd.c
@@ -597,7 +597,8 @@ static void sam_tsd_bottomhalf(void *arg)
        * this case; we rely on the timer expiry to get us going again.
        */
 
-      wd_start(priv->wdog, TSD_WDOG_DELAY, sam_tsd_expiry, 1, (uint32_t)priv);
+      (void)wd_start(priv->wdog, TSD_WDOG_DELAY, sam_tsd_expiry, 1,
+                     (uint32_t)priv);
       ier = 0;
       goto ignored;
     }
@@ -675,7 +676,8 @@ static void sam_tsd_bottomhalf(void *arg)
 
       /* Continue to sample the position while the pen is down */
 
-      wd_start(priv->wdog, TSD_WDOG_DELAY, sam_tsd_expiry, 1, (uint32_t)priv);
+      (void)wd_start(priv->wdog, TSD_WDOG_DELAY, sam_tsd_expiry, 1,
+                     (uint32_t)priv);
 
       /* Check the thresholds.  Bail if (1) this is not the first
        * measurement and (2) there is no significant difference from
diff --git a/arch/arm/src/sama5/sam_twi.c b/arch/arm/src/sama5/sam_twi.c
index 7e32dd7720..11f9cf8801 100644
--- a/arch/arm/src/sama5/sam_twi.c
+++ b/arch/arm/src/sama5/sam_twi.c
@@ -487,7 +487,7 @@ static int twi_wait(struct twi_dev_s *priv, unsigned int size)
    * TWI transfer stalls.
    */
 
-  wd_start(priv->timeout, timeout, twi_timeout, 1, (uint32_t)priv);
+  (void)wd_start(priv->timeout, timeout, twi_timeout, 1, (uint32_t)priv);
 
   /* Wait for either the TWI transfer or the timeout to complete */
 
diff --git a/arch/arm/src/samv7/sam_hsmci.c b/arch/arm/src/samv7/sam_hsmci.c
index b6df58bc18..4f5e0d87d9 100644
--- a/arch/arm/src/samv7/sam_hsmci.c
+++ b/arch/arm/src/samv7/sam_hsmci.c
@@ -2791,7 +2791,7 @@ static sdio_eventset_t sam_eventwait(FAR struct sdio_dev_s *dev,
       delay = MSEC2TICK(timeout);
       ret   = wd_start(priv->waitwdog, delay, (wdentry_t)sam_eventtimeout,
                        1, (uint32_t)priv);
-      if (ret != OK)
+      if (ret < 0)
         {
            mcerr("ERROR: wd_start failed: %d\n", ret);
         }
diff --git a/arch/arm/src/samv7/sam_qspi.c b/arch/arm/src/samv7/sam_qspi.c
index 80ce719c80..7e47c6caf9 100644
--- a/arch/arm/src/samv7/sam_qspi.c
+++ b/arch/arm/src/samv7/sam_qspi.c
@@ -885,7 +885,7 @@ static int qspi_memory_dma(struct sam_qspidev_s *priv,
 
       ret = wd_start(priv->dmadog, DMA_TIMEOUT_TICKS,
                      (wdentry_t)qspi_dma_timeout, 1, (uint32_t)priv);
-      if (ret != OK)
+      if (ret < 0)
         {
            spierr("ERROR: wd_start failed: %d\n", ret);
         }
diff --git a/arch/arm/src/samv7/sam_spi.c b/arch/arm/src/samv7/sam_spi.c
index e45fac7d00..0ae37af28b 100644
--- a/arch/arm/src/samv7/sam_spi.c
+++ b/arch/arm/src/samv7/sam_spi.c
@@ -1864,7 +1864,7 @@ static void spi_exchange(struct spi_dev_s *dev, const void *txbuffer,
 
       ret = wd_start(spics->dmadog, DMA_TIMEOUT_TICKS,
                      (wdentry_t)spi_dmatimeout, 1, (uint32_t)spics);
-      if (ret != OK)
+      if (ret < 0)
         {
            spierr("ERROR: wd_start failed: %d\n", ret);
         }
diff --git a/arch/arm/src/samv7/sam_twihs.c b/arch/arm/src/samv7/sam_twihs.c
index 261357c618..6c2d36b291 100644
--- a/arch/arm/src/samv7/sam_twihs.c
+++ b/arch/arm/src/samv7/sam_twihs.c
@@ -491,7 +491,8 @@ static int twi_wait(struct twi_dev_s *priv, unsigned int size)
    * TWIHS transfer stalls.
    */
 
-  wd_start(priv->timeout, (timeout * size), twi_timeout, 1, (uint32_t)priv);
+  (void)wd_start(priv->timeout, (timeout * size), twi_timeout, 1,
+                 (uint32_t)priv);
 
   /* Wait for either the TWIHS transfer or the timeout to complete */
 
diff --git a/arch/arm/src/stm32/stm32_sdio.c b/arch/arm/src/stm32/stm32_sdio.c
index 31ecd08604..1413334419 100644
--- a/arch/arm/src/stm32/stm32_sdio.c
+++ b/arch/arm/src/stm32/stm32_sdio.c
@@ -2500,7 +2500,7 @@ static sdio_eventset_t stm32_eventwait(FAR struct sdio_dev_s *dev,
       delay = MSEC2TICK(timeout);
       ret   = wd_start(priv->waitwdog, delay, (wdentry_t)stm32_eventtimeout,
                        1, (uint32_t)priv);
-      if (ret != OK)
+      if (ret < 0)
         {
           mcerr("ERROR: wd_start failed: %d\n", ret);
         }
diff --git a/arch/arm/src/stm32f7/stm32_sdmmc.c b/arch/arm/src/stm32f7/stm32_sdmmc.c
index e5ac6632df..c3530fc3fe 100644
--- a/arch/arm/src/stm32f7/stm32_sdmmc.c
+++ b/arch/arm/src/stm32f7/stm32_sdmmc.c
@@ -2691,7 +2691,7 @@ static sdio_eventset_t stm32_eventwait(FAR struct sdio_dev_s *dev,
       delay = MSEC2TICK(timeout);
       ret   = wd_start(priv->waitwdog, delay, (wdentry_t)stm32_eventtimeout,
                        1, (uint32_t)priv);
-      if (ret != OK)
+      if (ret < 0)
         {
           mcerr("ERROR: wd_start failed: %d\n", ret);
         }
diff --git a/arch/arm/src/stm32l4/stm32l4_qspi.c b/arch/arm/src/stm32l4/stm32l4_qspi.c
index 793fbb7ffa..025e71f6d1 100644
--- a/arch/arm/src/stm32l4/stm32l4_qspi.c
+++ b/arch/arm/src/stm32l4/stm32l4_qspi.c
@@ -1447,7 +1447,7 @@ static int qspi_memory_dma(struct stm32l4_qspidev_s *priv,
 
       ret = wd_start(priv->dmadog, DMA_TIMEOUT_TICKS,
                      (wdentry_t)qspi_dma_timeout, 1, (uint32_t)priv);
-      if (ret != OK)
+      if (ret < 0)
         {
            spierr("ERROR: wd_start failed: %d\n", ret);
         }
diff --git a/arch/arm/src/stm32l4/stm32l4_sdmmc.c b/arch/arm/src/stm32l4/stm32l4_sdmmc.c
index 6da267d2d0..2078c16258 100644
--- a/arch/arm/src/stm32l4/stm32l4_sdmmc.c
+++ b/arch/arm/src/stm32l4/stm32l4_sdmmc.c
@@ -2637,7 +2637,7 @@ static sdio_eventset_t stm32_eventwait(FAR struct sdio_dev_s *dev,
       delay = MSEC2TICK(timeout);
       ret   = wd_start(priv->waitwdog, delay, (wdentry_t)stm32_eventtimeout,
                        1, (uint32_t)priv);
-      if (ret != OK)
+      if (ret < 0)
         {
           mcerr("ERROR: wd_start failed: %d\n", ret);
         }
diff --git a/arch/mips/src/pic32mx/pic32mx-usbdev.c b/arch/mips/src/pic32mx/pic32mx-usbdev.c
index b184ff41ec..82b3185181 100644
--- a/arch/mips/src/pic32mx/pic32mx-usbdev.c
+++ b/arch/mips/src/pic32mx/pic32mx-usbdev.c
@@ -1031,7 +1031,8 @@ static void pic32mx_delayedrestart(struct pic32mx_usbdev_s *priv, uint8_t epno)
 
   /* And start (or re-start) the watchdog timer */
 
-  wd_start(priv->wdog, RESTART_DELAY, pic32mx_rqrestart, 1, (uint32_t)priv);
+  (void)wd_start(priv->wdog, RESTART_DELAY, pic32mx_rqrestart, 1,
+                 (uint32_t)priv);
 }
 
 /****************************************************************************
diff --git a/drivers/input/ads7843e.c b/drivers/input/ads7843e.c
index 195aaa0260..e62d2c2de3 100644
--- a/drivers/input/ads7843e.c
+++ b/drivers/input/ads7843e.c
@@ -607,7 +607,8 @@ static void ads7843e_worker(FAR void *arg)
        * later.
        */
 
-       wd_start(priv->wdog, ADS7843E_WDOG_DELAY, ads7843e_wdog, 1, (uint32_t)priv);
+       (void)wd_start(priv->wdog, ADS7843E_WDOG_DELAY, ads7843e_wdog, 1,
+                      (uint32_t)priv);
        goto ignored;
     }
   else
diff --git a/drivers/input/max11802.c b/drivers/input/max11802.c
index 1e40178df0..52ba527ed8 100644
--- a/drivers/input/max11802.c
+++ b/drivers/input/max11802.c
@@ -592,8 +592,8 @@ static void max11802_worker(FAR void *arg)
 
        iinfo("Previous pen up event still in buffer\n");
        max11802_notify(priv);
-       wd_start(priv->wdog, MAX11802_WDOG_DELAY, max11802_wdog, 1,
-                (uint32_t)priv);
+       (void)wd_start(priv->wdog, MAX11802_WDOG_DELAY, max11802_wdog, 1,
+                      (uint32_t)priv);
        goto ignored;
     }
   else
@@ -632,8 +632,8 @@ static void max11802_worker(FAR void *arg)
 
       /* Continue to sample the position while the pen is down */
 
-      wd_start(priv->wdog, MAX11802_WDOG_DELAY, max11802_wdog, 1,
-               (uint32_t)priv);
+      (void)wd_start(priv->wdog, MAX11802_WDOG_DELAY, max11802_wdog, 1,
+i                    (uint32_t)priv);
 
       /* Check if data is valid */
 
diff --git a/drivers/wireless/ieee80211/bcmf_driver.c b/drivers/wireless/ieee80211/bcmf_driver.c
index 1a3ae7f76e..6c17b2b7a9 100644
--- a/drivers/wireless/ieee80211/bcmf_driver.c
+++ b/drivers/wireless/ieee80211/bcmf_driver.c
@@ -886,8 +886,8 @@ int bcmf_wl_start_scan(FAR struct bcmf_dev_s *priv, struct iwreq *iwr)
 
   /*  Start scan_timeout timer */
 
-  wd_start(priv->scan_timeout, BCMF_SCAN_TIMEOUT_TICK,
-           bcmf_wl_scan_timeout, (wdparm_t)priv);
+  (void)wd_start(priv->scan_timeout, BCMF_SCAN_TIMEOUT_TICK,
+                 bcmf_wl_scan_timeout, (wdparm_t)priv);
 
   return OK;
 
diff --git a/drivers/wireless/ieee80211/bcmf_sdio.c b/drivers/wireless/ieee80211/bcmf_sdio.c
index 25f94ab303..d13276c263 100644
--- a/drivers/wireless/ieee80211/bcmf_sdio.c
+++ b/drivers/wireless/ieee80211/bcmf_sdio.c
@@ -665,8 +665,8 @@ int bcmf_bus_sdio_initialize(FAR struct bcmf_dev_s *priv,
 
   /* Start the waitdog timer */
 
-  wd_start(sbus->waitdog, BCMF_WAITDOG_TIMEOUT_TICK, bcmf_sdio_waitdog_timeout,
-           (wdparm_t)priv);
+  (void)wd_start(sbus->waitdog, BCMF_WAITDOG_TIMEOUT_TICK,
+                 bcmf_sdio_waitdog_timeout, (wdparm_t)priv);
 
   /* Spawn bcmf daemon thread */
 
@@ -760,8 +760,8 @@ int bcmf_sdio_thread(int argc, char **argv)
 
       /* Restart the waitdog timer */
 
-      wd_start(sbus->waitdog, BCMF_WAITDOG_TIMEOUT_TICK,
-               bcmf_sdio_waitdog_timeout, (wdparm_t)priv);
+      (void)wd_start(sbus->waitdog, BCMF_WAITDOG_TIMEOUT_TICK,
+                     bcmf_sdio_waitdog_timeout, (wdparm_t)priv);
 
       /* Wake up device */
 
diff --git a/fs/mount/fs_automount.c b/fs/mount/fs_automount.c
index e73ce50e24..41de262749 100644
--- a/fs/mount/fs_automount.c
+++ b/fs/mount/fs_automount.c
@@ -303,11 +303,8 @@ static int automount_unmount(FAR struct automounter_state_s *priv)
                              (uint32_t)((uintptr_t)priv));
               if (ret < 0)
                 {
-                  errcode = get_errno();
-                  DEBUGASSERT(errcode > 0);
-
-                  ferr("ERROR: wd_start failed: %d\n", errcode);
-                  return -ret;
+                  ferr("ERROR: wd_start failed: %d\n", ret);
+                  return ret;
                 }
             }
 
diff --git a/include/nuttx/wdog.h b/include/nuttx/wdog.h
index 7aacca711c..720d2b961c 100644
--- a/include/nuttx/wdog.h
+++ b/include/nuttx/wdog.h
@@ -1,7 +1,8 @@
 /****************************************************************************
  * include/nuttx/wdog.h
  *
- *   Copyright (C) 2007-2009, 2014-2015 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007-2009, 2014-2015, 2018 Gregory Nutt. All rights
+ *     reserved.
  *   Author: Gregory Nutt <gnutt@nuttx.org>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -196,7 +197,8 @@ WDOG_ID wd_create(void);
  *          watchdog structure.
  *
  * Return Value:
- *   Returns OK or ERROR
+ *   Zero (OK) is returned on success; a negated errno value is return to
+ *   indicate the nature of any failure.
  *
  * Assumptions:
  *   The caller has assured that the watchdog is no longer in use.
@@ -230,7 +232,8 @@ int wd_delete(WDOG_ID wdog);
  *   parm1..4 - parameters to pass to wdentry
  *
  * Return Value:
- *   OK or ERROR
+ *   Zero (OK) is returned on success; a negated errno value is return to
+ *   indicate the nature of any failure.
  *
  * Assumptions:
  *   The watchdog routine runs in the context of the timer interrupt handler
diff --git a/sched/mqueue/mq_timedreceive.c b/sched/mqueue/mq_timedreceive.c
index 9194a79da7..af95097e89 100644
--- a/sched/mqueue/mq_timedreceive.c
+++ b/sched/mqueue/mq_timedreceive.c
@@ -239,8 +239,8 @@ ssize_t nxmq_timedreceive(mqd_t mqdes, FAR char *msg, size_t msglen,
 
       /* Start the watchdog */
 
-      wd_start(rtcb->waitdog, ticks, (wdentry_t)nxmq_rcvtimeout,
-               1, getpid());
+      (void)wd_start(rtcb->waitdog, ticks, (wdentry_t)nxmq_rcvtimeout,
+                     1, getpid());
     }
 
   /* Get the message from the message queue */
diff --git a/sched/mqueue/mq_timedsend.c b/sched/mqueue/mq_timedsend.c
index 43924d4901..66682e68f7 100644
--- a/sched/mqueue/mq_timedsend.c
+++ b/sched/mqueue/mq_timedsend.c
@@ -271,7 +271,8 @@ int nxmq_timedsend(mqd_t mqdes, FAR const char *msg, size_t msglen, int prio,
 
   /* Start the watchdog and begin the wait for MQ not full */
 
-  wd_start(rtcb->waitdog, ticks, (wdentry_t)nxmq_sndtimeout, 1, getpid());
+  (void)wd_start(rtcb->waitdog, ticks, (wdentry_t)nxmq_sndtimeout,
+                 1, getpid());
 
   /* And wait for the message queue to be non-empty */
 
diff --git a/sched/pthread/pthread_condtimedwait.c b/sched/pthread/pthread_condtimedwait.c
index b27c279397..66410faebd 100644
--- a/sched/pthread/pthread_condtimedwait.c
+++ b/sched/pthread/pthread_condtimedwait.c
@@ -274,8 +274,10 @@ int pthread_cond_timedwait(FAR pthread_cond_t *cond, FAR pthread_mutex_t *mutex,
                     {
                       /* Start the watchdog */
 
-                      wd_start(rtcb->waitdog, ticks, (wdentry_t)pthread_condtimedout,
-                               2, (uint32_t)mypid, (uint32_t)SIGCONDTIMEDOUT);
+                      (void)wd_start(rtcb->waitdog, ticks,
+                                     (wdentry_t)pthread_condtimedout,
+                                     2, (uint32_t)mypid,
+                                     (uint32_t)SIGCONDTIMEDOUT);
 
                       /* Take the condition semaphore.  Do not restore interrupts
                        * until we return from the wait.  This is necessary to
diff --git a/sched/signal/sig_timedwait.c b/sched/signal/sig_timedwait.c
index 948c91723d..01b735ffec 100644
--- a/sched/signal/sig_timedwait.c
+++ b/sched/signal/sig_timedwait.c
@@ -356,8 +356,8 @@ int nxsig_timedwait(FAR const sigset_t *set, FAR struct siginfo *info,
 
               /* Start the watchdog */
 
-              wd_start(rtcb->waitdog, waitticks, (wdentry_t)nxsig_timeout,
-                       1, wdparm.pvarg);
+              (void)wd_start(rtcb->waitdog, waitticks,
+                             (wdentry_t)nxsig_timeout, 1, wdparm.pvarg);
 
               /* Now wait for either the signal or the watchdog */
 
diff --git a/sched/timer/timer_settime.c b/sched/timer/timer_settime.c
index 9be2104c35..3724ed5ebd 100644
--- a/sched/timer/timer_settime.c
+++ b/sched/timer/timer_settime.c
@@ -1,7 +1,8 @@
 /****************************************************************************
  * sched/timer/timer_settime.c
  *
- *   Copyright (C) 2007-2010, 2013-2016 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007-2010, 2013-2016, 2018 Gregory Nutt. All rights
+ *     reserved.
  *   Author: Gregory Nutt <gnutt@nuttx.org>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -390,6 +391,15 @@ int timer_settime(timer_t timerid, int flags,
       timer->pt_last = delay;
       ret = wd_start(timer->pt_wdog, delay, (wdentry_t)timer_timeout,
                      1, (uint32_t)((wdparm_t)timer));
+      if (ret < 0)
+        {
+          set_errno(-ret);
+          ret = ERROR;
+        }
+      else
+        {
+          ret = OK;
+        }
     }
 
   leave_critical_section(intflags);
diff --git a/sched/wdog/wd_delete.c b/sched/wdog/wd_delete.c
index 7b56bede46..785d4ec87c 100644
--- a/sched/wdog/wd_delete.c
+++ b/sched/wdog/wd_delete.c
@@ -68,7 +68,8 @@
  *          watchdog structure.
  *
  * Return Value:
- *   Returns OK or ERROR
+ *   Zero (OK) is returned on success; a negated errno value is return to
+ *   indicate the nature of any failure.
  *
  * Assumptions:
  *   The caller has assured that the watchdog is no longer in use.
diff --git a/sched/wdog/wd_start.c b/sched/wdog/wd_start.c
index f94f9c2320..f861cbfab7 100644
--- a/sched/wdog/wd_start.c
+++ b/sched/wdog/wd_start.c
@@ -1,7 +1,8 @@
 /****************************************************************************
  * sched/wdog/wd_start.c
  *
- *   Copyright (C) 2007-2009, 2012, 2014, 2016 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007-2009, 2012, 2014, 2016, 2018 Gregory Nutt.  All
+ *     rights reserved.
  *   Author: Gregory Nutt <gnutt@nuttx.org>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -103,8 +104,6 @@ typedef void (*wdentry4_t)(int argc, wdparm_t arg1, wdparm_t arg2,
  * Return Value:
  *   None
  *
- * Assumptions:
- *
  ****************************************************************************/
 
 static inline void wd_expiration(void)
@@ -211,7 +210,8 @@ static inline void wd_expiration(void)
  *   parm1..4 - parameters to pass to wdentry
  *
  * Return Value:
- *   OK or ERROR
+ *   Zero (OK) is returned on success; a negated errno value is return to
+ *   indicate the nature of any failure.
  *
  * Assumptions:
  *   The watchdog routine runs in the context of the timer interrupt handler
@@ -229,12 +229,11 @@ int wd_start(WDOG_ID wdog, int32_t delay, wdentry_t wdentry,  int argc, ...)
   irqstate_t flags;
   int i;
 
-  /* Verify the wdog */
+  /* Verify the wdog and setup parameters */
 
-  if (!wdog || argc > CONFIG_MAX_WDOGPARMS || delay < 0)
+  if (wdog == NULL || argc > CONFIG_MAX_WDOGPARMS || delay < 0)
     {
-      set_errno(EINVAL);
-      return ERROR;
+      return -EINVAL;
     }
 
   /* Check if the watchdog has been started. If so, stop it.