diff --git a/src/dds.rs b/src/dds.rs
index 5a39308..df3b618 100644
--- a/src/dds.rs
+++ b/src/dds.rs
@@ -66,6 +66,7 @@ const READ_MASK		:u8 = 0x80;
 pub struct DDS<SPI> {
 	spi: SPI,
 	f_ref_clk: u64,
+	f_sys_clk: u64,
 }
 
 impl<SPI, E> DDS<SPI>
@@ -76,6 +77,7 @@ where
 		DDS {
 			spi,
 			f_ref_clk,
+			f_sys_clk: f_ref_clk,
 		}
 	}
 }
@@ -119,7 +121,9 @@ where
 			(DDSCFRMask::REFCLK_IN_DIV_BYPASS, 0),
 			// Ensure divider is not reset
 			(DDSCFRMask::REFCLK_IN_DIV_RESETB, 1),
-		])
+		])?;
+		self.f_sys_clk = self.f_ref_clk / 2;
+		Ok(())
 	}
 
 	pub fn enable_normal_ref_clk(&mut self) -> Result<(), Error<E>> {
@@ -130,7 +134,9 @@ where
 			(DDSCFRMask::REFCLK_IN_DIV_BYPASS, 1),
 			// Reset does not matter
 			(DDSCFRMask::REFCLK_IN_DIV_RESETB, 1),
-		])
+		])?;
+		self.f_sys_clk = self.f_ref_clk;
+		Ok(())
 	}
 
 	pub fn enable_pll(&mut self, f_sys_clk: u64) -> Result<(), Error<E>> {
@@ -170,16 +176,19 @@ where
 		])?;
 		self.set_configurations(&mut [
 			(DDSCFRMask::PFD_RESET, 0),
-		])
+		])?;
+		self.f_sys_clk = self.f_ref_clk * divider;
+		Ok(())
 	}
 
 	// Change external clock source (ref_clk)
 	pub fn set_ref_clk_frequency(&mut self, f_ref_clk: u64) {
 		self.f_ref_clk = f_ref_clk;
+		// TODO: Examine clock tree and update f_sys_clk
 	}
 
 	/*
-	 *  Impleement configurations registers I/O through bitmasks
+	 *  Implement configurations registers I/O through bitmasks
 	 *
 	 *  Get all (cfr1, cfr2, cfr3) contents
 	 */
@@ -246,6 +255,41 @@ where
 		self.set_all_configurations(data_array.clone())
 	}
 
+	/*
+	 *  Set a single tone profile
+	 *  Phase: Expressed in positive degree
+	 *  Frequency: Must be integer
+	 *  Amplitude: In a scale from 0 to 1, taking float
+	 */
+	pub fn set_single_tone_profile(&mut self, profile: u8, f_out: u64, phase_offset: f64, amp_scale_factor: f64) -> Result<(), Error<E>> {
+
+		assert!(profile < 8);
+		assert!(phase_offset >= 0.0 && phase_offset < 360.0);
+		assert!(amp_scale_factor >=0.0 && amp_scale_factor <= 1.0);
+
+		let resolutions :[u64; 3] = [1 << 32, 1 << 16, 1 << 14];
+		let ftw = (resolutions[0] * f_out / self.f_sys_clk) as u32;
+		let pow = ((resolutions[1] as f64) * phase_offset / 360.0) as u16;
+		let asf = ((resolutions[2] as f64) * amp_scale_factor) as u16;
+		// Setup configuration registers before writing single tone register
+		self.set_configurations(&mut [
+			(DDSCFRMask::RAM_ENABLE, 0),
+			(DDSCFRMask::DIGITAL_RAMP_ENABLE, 0),
+			(DDSCFRMask::PARALLEL_DATA_PORT_ENABLE, 0),
+		])?;
+		// Transfer single tone profile data
+		self.write_register(0x0E + profile, &mut [
+			((asf >> 8 ) & 0xFF) as u8,
+			((asf >> 0 ) & 0xFF) as u8,
+			((pow >> 8 ) & 0xFF) as u8,
+			((pow >> 0 ) & 0xFF) as u8,
+			((ftw >> 24) & 0xFF) as u8,
+			((ftw >> 16) & 0xFF) as u8,
+			((ftw >> 8 ) & 0xFF) as u8,
+			((ftw >> 0 ) & 0xFF) as u8,
+		])
+	}
+
 }
 
 macro_rules! impl_register_io {