Implement serial receive DMA for the F1xx. This is not quite working right yet. Some clients work, others not so much.

apps/drivers/boards/px4io/px4io_init.c

@@ -95,4 +95,25 @@ __EXPORT void stm32_boardinitialize(void)
 
 	stm32_configgpio(GPIO_ADC_VBATT);
 	stm32_configgpio(GPIO_ADC_IN5);
+
+	/* set up the serial DMA polling */
+#ifdef SERIAL_HAVE_DMA
+	{
+		static struct hrt_call serial_dma_call;
+		struct timespec ts;
+
+		/*
+		 * Poll at 1ms intervals for received bytes that have not triggered
+		 * a DMA event.
+		 */
+		ts.tv_sec = 0;
+		ts.tv_nsec = 1000000;
+
+		hrt_call_every(&serial_dma_call,
+			       ts_to_abstime(&ts),
+			       ts_to_abstime(&ts),
+			       (hrt_callout)stm32_serial_dma_poll,
+			       NULL);
+	}
+#endif
 }