Add FIFO reset function and return periods per DFT to GUI.

src/ad5940.rs

@@ -765,6 +765,17 @@ impl AD5940 {
         Ok((data >> 16) & 0x7FF)  
     }
 
+    pub async fn clear_and_enable_fifo(&mut self) -> Result<(), Error> {
+        let mut fifocon = self.read_reg(Register::FIFOCON).await?;
+        fifocon = DATAFIFOEN::apply(fifocon, DATAFIFOEN::FIFOisReset as u32); // Disable FIFO
+        self.write_reg(Register::FIFOCON, fifocon).await?;
+
+        fifocon = DATAFIFOEN::apply(fifocon, DATAFIFOEN::Normal as u32); // Enable FIFO
+        self.write_reg(Register::FIFOCON, fifocon).await?;
+
+        Ok(())
+    }
+
     pub async fn init_waveform(&mut self) -> Result<(), Error> {
         // Set frequency
         let freq: u32 = 1000;