diff --git a/charon_vna/gui.py b/charon_vna/gui.py
index 6ac734a..996d7b4 100644
--- a/charon_vna/gui.py
+++ b/charon_vna/gui.py
@@ -105,7 +105,7 @@ class MainWindow(QMainWindow):
         prog_sweep.setMaximum(100)
         prog_sweep.setFormat("%v / %m")
         # prog_sweep.setTextVisible(False)
-        prog_sweep.setValue(50)
+        prog_sweep.setValue(0)
         window_layout.addWidget(prog_sweep)
         self.prog_sweep = prog_sweep
 
diff --git a/charon_vna/vna.py b/charon_vna/vna.py
index f1c43b5..b3bc2f6 100644
--- a/charon_vna/vna.py
+++ b/charon_vna/vna.py
@@ -1,11 +1,11 @@
 # %% imports
 import copy
+from enum import IntEnum, unique
 from pathlib import Path
-from typing import Any, Callable, Dict, Tuple
+from typing import Any, Callable, Dict, Literal, Tuple
 
 import adi
-
-# import iio
+import iio
 import numpy as np
 import skrf as rf
 import xarray as xr
@@ -34,6 +34,38 @@ def generate_tone(f: float, fs: float, N: int = 1024, scale: int = 2**14):
     return iq
 
 
+@unique
+class AD9361Register(IntEnum):
+    AUXDAC1_WORD = 0x018
+    AUXDAC2_WORD = 0x019
+    AUXDAC1_CONFIG = 0x01A
+    AUXDAC2_CONFIG = 0x01B
+    AUXADC_CLOCK_DIVIDER = 0x01C
+    AUXADC_CONFIG = 0x01D
+    AUXADC_WORD_MSB = 0x01E
+    AUXADC_WORD_LSB = 0x01F
+    AUTO_GPIO = 0x020
+    AGC_GAIN_LOCK_DELAY = 0x021
+    AGC_ATTACK_DELAY = 0x022
+    AUXDAC_ENABLE_CONTROL = 0x023
+    RX_LOAD_SYNTH_DELAY = 0x024
+    TX_LOAD_SYNTH_DELAY = 0x025
+    EXTERNAL_LNA_CONTROL = 0x026
+    GPO_FORCE_AND_INIT = 0x027
+    GPO0_RX_DELAY = 0x028
+    GPO1_RX_DELAY = 0x029
+    GPO2_RX_DELAY = 0x02A
+    GPO3_RX_DELAY = 0x02B
+    GPO0_TX_DELAY = 0x02C
+    GPO1_TX_DELAY = 0x02D
+    GPO2_TX_DELAY = 0x02E
+    GPO3_TX_DELAY = 0x02F
+    AUXDAC1_RX_DELAY = 0x030
+    AUXDAC1_TX_DELAY = 0x031
+    AUXDAC2_RX_DELAY = 0x032
+    AUXDAC2_TX_DELAY = 0x033
+
+
 class Charon:
     FREQUENCY_OFFSET = 1e6
 
@@ -49,7 +81,8 @@ class Charon:
         self.frequency = frequency
 
         # everything RF
-        self.sdr = adi.ad9361(uri=f"ip:{ip}")
+        uri = f"ip:{ip}"
+        self.sdr = adi.ad9361(uri=uri)
         for attr, expected in [
             ("adi,2rx-2tx-mode-enable", True),
             # ("adi,gpo-manual-mode-enable", True),
@@ -81,14 +114,16 @@ class Charon:
         self.sdr.tx_hardwaregain_chan0 = -10
 
         # # switch control
-        # ctx = iio.Context(uri)
-        # self.ctrl = ctx.find_device("ad9361-phy")
-        # # raw ad9361 register accesss:
-        # # https://ez.analog.com/linux-software-drivers/f/q-a/120853/control-fmcomms3-s-gpo-with-python
-        # # https://www.analog.com/media/cn/technical-documentation/user-guides/ad9364_register_map_reference_manual_ug-672.pdf  # noqa: E501
-        # self.ctrl.reg_write(0x26, 0x90)  # bit 7: AuxDAC Manual, bit 4: GPO Manual
-        # self._set_gpo(self.ports[0] - 1)
-        # # TODO: init AuxDAC
+        ctx = iio.Context(uri)
+        self.ctrl = ctx.find_device("ad9361-phy")
+        # raw ad9361 register accesss:
+        # https://ez.analog.com/linux-software-drivers/f/q-a/120853/control-fmcomms3-s-gpo-with-python
+        # https://www.analog.com/media/cn/technical-documentation/user-guides/ad9364_register_map_reference_manual_ug-672.pdf  # noqa: E501
+        self.ctrl.reg_write(AD9361Register.EXTERNAL_LNA_CONTROL, 0x90)  # bit 7: AuxDAC Manual, bit 4: GPO Manual
+        self.ctrl.reg_write(AD9361Register.AUXDAC_ENABLE_CONTROL, 0x3F)
+        self._set_gpo(0b0000)
+        self._set_dac(value=0, channel=1)
+        self._set_dac(value=0, channel=2)
 
     def get_config(self) -> Dict[str, Any]:
         config = dict()
@@ -113,10 +148,45 @@ class Charon:
         return config
 
     def _get_gpo(self) -> int:
-        return (self.ctrl.reg_read(0x27) >> 4) & 0x0F
+        return (self.ctrl.reg_read(AD9361Register.GPO_FORCE_AND_INIT) >> 4) & 0x0F
 
     def _set_gpo(self, value: int) -> None:
-        self.ctrl.reg_write(0x27, (value & 0x0F) << 4)  # bits 7-4: GPO3-0
+        self.ctrl.reg_write(AD9361Register.GPO_FORCE_AND_INIT, (value & 0x0F) << 4)  # bits 7-4: GPO3-0
+
+    def _set_dac(self, value: int, channel: Literal[1, 2]):
+        if channel not in [1, 2]:
+            raise ValueError(f"Invalid channel {channel}. Must be 1 or 2")
+
+        if value > 0x3FF or value < 0:
+            raise ValueError("Invalid value for 10 bit DAC. Must be between 0 and 0x3FF (inclusive)")
+
+        @unique
+        class Vref(IntEnum):
+            VREF_1V0 = 0b00
+            VREF_1V5 = 0b01
+            VREF_2V0 = 0b10
+            VREF_2V5 = 0b11
+
+        @unique
+        class StepFactor(IntEnum):
+            FACTOR_2 = 0b0
+            FACTOR_1 = 0b1
+
+        # https://www.analog.com/media/cn/technical-documentation/user-guides/ad9364_register_map_reference_manual_ug-672.pdf
+        # page 13
+        # vout = 0.97 * vref + (0.000738 + 9e-6 * (vref * 1.6 - 2)) * auxdac_word[9:0] * step_factor - 0.3572 * step_factor + 0.05
+        # vout ~= (vref - 0.3572 * step_factor) + 0.000738 * auxdac_word[9:0] * step_factor
+        # which gives a 1.5V swing with step_factor == 2 and 0.75V swing with step_factor == 1
+        # vref basically just changes the minimum voltage with negligible impact on output scaling
+
+        self.ctrl.reg_write(
+            AD9361Register.__getitem__(f"AUXDAC{channel}_WORD"),
+            (value >> 2) & 0xFF,
+        )
+        self.ctrl.reg_write(
+            AD9361Register.__getitem__(f"AUXDAC{channel}_CONFIG"),
+            (value & 0x3) | (Vref.VREF_1V0.value << 2) | (StepFactor.FACTOR_2 << 4),
+        )
 
     def set_output_power(self, power: float):
         # FIXME: this is a hack because I don't want to go through re-calibration