diff --git a/core/esp_phy.c b/core/esp_phy.c
new file mode 100644
index 0000000..36ce915
--- /dev/null
+++ b/core/esp_phy.c
@@ -0,0 +1,32 @@
+/** esp/phy.h
+ *
+ * PHY hardware management functions.
+ *
+ * Part of esp-open-rtos
+ * Copyright (C) 2016 ChefSteps, Inc
+ * BSD Licensed as described in the file LICENSE
+ */
+#include <esp/phy.h>
+#include <esp/gpio.h>
+
+void bt_coexist_configure(bt_coexist_mode_t mode, uint8_t bt_active_pin, uint8_t bt_priority_pin)
+{
+    /* Disable coexistence entirely before changing pin assignments */
+    GPIO.OUT &= ~(GPIO_OUT_BT_COEXIST_MASK);
+    uint32_t new_mask = 0;
+
+    new_mask = VAL2FIELD_M(GPIO_OUT_BT_ACTIVE_PIN, bt_active_pin) +
+        VAL2FIELD_M(GPIO_OUT_BT_PRIORITY_PIN, bt_priority_pin);
+
+    if(mode == BT_COEXIST_USE_BT_ACTIVE || mode == BT_COEXIST_USE_BT_ACTIVE_PRIORITY) {
+        gpio_enable(bt_active_pin, GPIO_INPUT);
+        new_mask |= GPIO_OUT_BT_ACTIVE_ENABLE;
+    }
+    if(mode == BT_COEXIST_USE_BT_ACTIVE_PRIORITY) {
+        gpio_enable(bt_priority_pin, GPIO_INPUT);
+        new_mask |= GPIO_OUT_BT_PRIORITY_ENABLE;
+    }
+    GPIO.OUT |= new_mask;
+}
+
+
diff --git a/core/include/esp/gpio.h b/core/include/esp/gpio.h
index c6fa42f..426d1ea 100644
--- a/core/include/esp/gpio.h
+++ b/core/include/esp/gpio.h
@@ -81,9 +81,9 @@ static inline void gpio_set_output_on_sleep(const uint8_t gpio_num, bool enabled
 static inline void gpio_write(const uint8_t gpio_num, const bool set)
 {
     if (set)
-        GPIO.OUT_SET = BIT(gpio_num);
+        GPIO.OUT_SET = BIT(gpio_num) & GPIO_OUT_PIN_MASK;
     else
-        GPIO.OUT_CLEAR = BIT(gpio_num);
+        GPIO.OUT_CLEAR = BIT(gpio_num) & GPIO_OUT_PIN_MASK;
 }
 
 /* Toggle output of a pin
@@ -102,9 +102,9 @@ static inline void gpio_toggle(const uint8_t gpio_num)
        task's pins, without needing to disable/enable interrupts.
     */
     if(GPIO.OUT & BIT(gpio_num))
-        GPIO.OUT_CLEAR = BIT(gpio_num);
+        GPIO.OUT_CLEAR = BIT(gpio_num) & GPIO_OUT_PIN_MASK;
     else
-        GPIO.OUT_SET = BIT(gpio_num);
+        GPIO.OUT_SET = BIT(gpio_num) & GPIO_OUT_PIN_MASK;
 }
 
 /* Read input value of a GPIO pin.
diff --git a/core/include/esp/gpio_regs.h b/core/include/esp/gpio_regs.h
index 815e7c1..6ff1f92 100644
--- a/core/include/esp/gpio_regs.h
+++ b/core/include/esp/gpio_regs.h
@@ -61,6 +61,21 @@ struct GPIO_REGS {
 
 _Static_assert(sizeof(struct GPIO_REGS) == 0x74, "GPIO_REGS is the wrong size");
 
+/* Details for additional OUT register fields */
+
+/* Bottom 16 bits of GPIO.OUT are for GPIOs 0-15, but upper 16 bits
+   are used to configure the input signalling pins for Bluetooth
+   Coexistence config (see esp/phy.h for a wrapper function).
+*/
+#define GPIO_OUT_PIN_MASK 0x0000FFFF
+#define GPIO_OUT_BT_COEXIST_MASK 0x03FF0000
+#define GPIO_OUT_BT_ACTIVE_ENABLE BIT(24)
+#define GPIO_OUT_BT_PRIORITY_ENABLE BIT(25)
+#define GPIO_OUT_BT_ACTIVE_PIN_M 0x0F
+#define GPIO_OUT_BT_ACTIVE_PIN_S 16
+#define GPIO_OUT_BT_PRIORITY_PIN_M 0x0F
+#define GPIO_OUT_BT_PRIORITY_PIN_S 20
+
 /* Details for CONF[i] registers */
 
 /* GPIO.CONF[i] control the pin behavior for the corresponding GPIO in/output.
diff --git a/core/include/esp/phy.h b/core/include/esp/phy.h
new file mode 100644
index 0000000..a597267
--- /dev/null
+++ b/core/include/esp/phy.h
@@ -0,0 +1,58 @@
+/** esp/phy.h
+ *
+ * PHY hardware management functions.
+ *
+ * These are not enough to configure the ESP8266 PHY by themselves
+ * (yet), but they provide utilities to modify the configuration set
+ * up via the SDK.
+ *
+ * Functions implemented here deal directly with the hardware, not the
+ * SDK software layers.
+ *
+ * Part of esp-open-rtos
+ * Copyright (C) 2016 ChefSteps, Inc
+ * BSD Licensed as described in the file LICENSE
+ */
+#ifndef _ESP_PHY_H
+#define _ESP_PHY_H
+
+#include <esp/types.h>
+#include <common_macros.h>
+
+#include <stdint.h>
+
+typedef enum {
+    BT_COEXIST_NONE,
+    BT_COEXIST_USE_BT_ACTIVE,
+    BT_COEXIST_USE_BT_ACTIVE_PRIORITY,
+} bt_coexist_mode_t;
+
+/** Override the Bluetooth Coexistence BT_ACTIVE pin setting
+    taken from the phy_info structure.
+
+    This enables other pins to be used for Bluetooth Coexistence
+    signals (rather than just the two provided for by phy_info). (Note
+    that not that not all pins are confirmed to work, GPIO 0 is
+    confirmed not usable as the SDK configures it as the WLAN_ACTIVE
+    output - even if you change the pin mode the SDK will change it
+    back.)
+
+    To change pins and have coexistence work successfully the BT
+    coexistence feature must be enabled in the phy_info configuration
+    (get_default_phy_info()). You can then modify the initial
+    configuration by calling this function from your own user_init
+    function.
+
+    (Eventually we should be able to support enough PHY registers
+    to enable coexistence without SDK support at all, but not yet.)
+
+    This function will enable bt_active_pin & bt_priority_as GPIO
+    inputs, according to the mode parameter.
+
+    Remember that the default Bluetooth Coexistence pins will be
+    configured as GPIOs by the SDK already, so you may want to
+    reconfigure/re-iomux them after calling this function.
+*/
+void bt_coexist_configure(bt_coexist_mode_t mode, uint8_t bt_active_pin, uint8_t bt_priority_pin);
+
+#endif