drivers/sx127x: Add RX Timeout support

This commit adds support to fix RX timeout for SX127x, it is done
leaving the RX mode, entering in stanby mode and returning to RX
mode. It is enough to fix the AFC and get communication working
again.

Signed-off-by: Alan C. Assis <acassis@gmail.com>

Author: acassis

drivers/wireless/lpwan/sx127x/Kconfig

@@ -50,6 +50,18 @@ config LPWAN_SX127X_RXFIFO_DATA_LEN
 	int "SX127X RX FIFO data length"
 	default 64
 
+config LPWAN_SX127X_RX_TIMEOUT
+	int "SX127X RX Timeout in Milliseconds"
+	default 10000
+	---help---
+		If device stopped receiving data for more than
+		LPWAN_SX127X_RX_TIMEOUT milliseconds it means the
+		frequency drift is too high that AFC failed to fix
+		the reception frequency. So if we leave the RX mode,
+		entering in standby and returning will clear the
+		AFC and fix the communication again.
+		If you don't want to use RX timeout set it to -1.
+
 endif #LPWAN_SX127X_RXSUPPORT
 
 config LPWAN_SX127X_TXSUPPORT

drivers/wireless/lpwan/sx127x/sx127x.c

@@ -316,10 +316,12 @@ struct sx127x_dev_s
   bool     pa_force;              /* Force PA BOOST pin select */
 #endif
 #ifdef CONFIG_LPWAN_SX127X_RXSUPPORT
-  uint32_t rx_timeout;            /* RX timeout (not supported) */
+  uint32_t rx_timeout;            /* RX timeout in milliseconds */
   uint16_t rx_fifo_len;           /* Number of bytes stored in fifo */
   uint16_t nxt_read;              /* Next read index */
   uint16_t nxt_write;             /* Next write index */
+  clock_t  last_rx_tick;          /* Ticks since last RX event to detect timeout */
+  struct work_s rx_watchdog;      /* Watchdog to detect timeout */
 
   /* Circular RX packet buffer */
 
@@ -1276,6 +1278,50 @@ static int sx127x_poll(FAR struct file *filep, FAR struct pollfd *fds,
 #endif
 }
 
+/****************************************************************************
+ * Name: sx127x_rx_watchdog
+ *
+ * Description:
+ *   Watchdog to detect SX127x RX communication stall
+ *
+ ****************************************************************************/
+
+#ifdef CONFIG_LPWAN_SX127X_RXSUPPORT
+static void sx127x_rx_watchdog(FAR void *arg)
+{
+  FAR struct sx127x_dev_s *dev = (FAR struct sx127x_dev_s *) arg;
+  clock_t now = clock_systime_ticks();
+
+  if (dev->opmode == SX127X_OPMODE_RX &&
+      (now - dev->last_rx_tick) > MSEC2TICK(dev->rx_timeout))
+    {
+      wlerr("RX stall detected, restarting RX\n");
+
+      /* Leave RX mode to clear AFC + bit sync */
+
+      sx127x_opmode_set(dev, SX127X_OPMODE_STANDBY);
+
+      /* datasheet-safe delay */
+
+      up_udelay(100);
+
+      /* Re-enter RX */
+
+      sx127x_opmode_set(dev, SX127X_OPMODE_RX);
+
+      /* Avoid using old RX tick, otherwise it always will fail */
+
+      dev->last_rx_tick = now;
+    }
+
+  /* Reschedule watchdog */
+
+  work_queue(LPWORK, &dev->rx_watchdog,
+             sx127x_rx_watchdog, dev,
+             MSEC2TICK(dev->rx_timeout));
+}
+#endif
+
 /****************************************************************************
  * Name: sx127x_lora_isr0_process
  *
@@ -1471,6 +1517,21 @@ static int sx127x_fskook_isr0_process(FAR struct sx127x_dev_s *dev)
               ret = sx127x_fskook_rxhandle(dev);
               if (ret > 0)
                 {
+                  /* Should we take care of RX timeout? */
+
+                  if (dev->rx_timeout > 0)
+                    {
+                      /* Keep a track of last RX time to detect timeout */
+
+                      dev->last_rx_tick = clock_systime_ticks();
+
+                      /* Prepare the work queue to take care of RX timeout */
+
+                      work_queue(LPWORK, &dev->rx_watchdog,
+                                 sx127x_rx_watchdog, dev,
+                                 MSEC2TICK(dev->rx_timeout));
+                    }
+
                   if (dev->pfd)
                     {
                       /* Data available for input */
@@ -4614,6 +4675,9 @@ int sx127x_register(FAR struct spi_dev_s *spi,
   dev->crcon          = CONFIG_LPWAN_SX127X_CRCON;
 #ifdef CONFIG_LPWAN_SX127X_FSKOOK
   dev->fskook.fixlen  = false;
+#  ifdef CONFIG_LPWAN_SX127X_TXSUPPORT
+  dev->rx_timeout     = CONFIG_LPWAN_SX127X_RX_TIMEOUT;
+#  endif
 #endif
 #ifdef CONFIG_LPWAN_SX127X_LORA
   dev->lora.invert_iq = false;