diff --git a/inc/gpio.h b/inc/gpio.h
--- a/inc/gpio.h
+++ b/inc/gpio.h
@@ -4,6 +4,14 @@
 #include "stm32f0xx_hal.h"
 
 
+enum _blinkrate
+{
+    BLINK_FAST = 50,
+    BLINK_MED = 250, 
+    BLINK_SLOW = 500
+}
+
+
 #define OSC_EN_Pin GPIO_PIN_1
 #define OSC_EN_GPIO_Port GPIOF
 #define OSC_NOTEN OSC_EN_GPIO_Port , OSC_EN_Pin
diff --git a/src/main.c b/src/main.c
--- a/src/main.c
+++ b/src/main.c
@@ -12,6 +12,19 @@
 #include "gps.h"
 
 
+// We have access to the 1PPS pin of the gps... could have trim routine for internal oscillator based on this when we have a fix
+// Probabl wake up 1 minute early -- 0.45min possible +/- on wakeup time with 15min sync intervals
+
+
+enum _state
+{
+    SYSTEM_POWERUP_SYNC = 0, // on powerup, get a GPS fix and set the RTC
+    SYSTEM_IDLE, // awaiting RTC interrupt for wakeup TODO wake up before scheduled time to get fix?
+    SYSTEM_GPSACQ, // RTC interrupted
+    SYSTEM_WSPRTX, // Wait for timeslot and actually transmit the message
+}
+
+
 int main(void)
 {
     HAL_Init();
@@ -21,80 +34,89 @@ int main(void)
     adc_init();
     i2c_init();
     gps_init();
-
-    //jtencode_init();
-
-    HAL_Delay(300);
-
-    //gps_poweroff();
-
-    // Disable ICs
-    HAL_GPIO_WritePin(OSC_NOTEN, 1);
-    HAL_GPIO_WritePin(TCXO_EN, 0);
+    wspr_init();
 
     uint32_t led_timer = HAL_GetTick();
-    uint32_t last_gps  = HAL_GetTick();
-    uint32_t last_wspr  = HAL_GetTick(); //0xfffff; // start immediately.
-
 
     led_blink(4);
 
-    uint8_t lastMinute = 0;
-    uint16_t blink_rate = 250;
+    uint16_t blink_rate = BLINK_FAST;
+    uint8_t state = SYSTEM_GPSACQ;
 
-    gps_poweron();
-    HAL_Delay(500);
-    gps_update_position();
 
     while (1)
     {
-        // TODO: Trigger this when RTC thinks its time to go
-        if(HAL_GetTick() - last_wspr > 500)
+        switch(state)
         {
-            switch(gps_getstate())
+
+            // Idling: sleep and wait for RTC timeslot trigger
+            case SYSTEM_IDLE:
+            {
+                blink_rate = BLINK_SLOW;
+                // Wait for RTC wakeup interrupt
+                wfi();
+                //enter_sleep();
+
+                // Somehow go to another state when we get an interrupt
+                state = SYSTEM_GPSACQ;
+            } break;
+
+
+            // Attempt to acquire GPS fix
+            case SYSTEM_GPSACQ:
             {
-                case GPS_STATE_ACQUIRING:
-                    blink_rate = 250;
-                    break;
-                case GPS_STATE_FRESHFIX:
-                    blink_rate = 50;
-                    break;
-                case GPS_STATE_STALEFIX:
-                case GPS_STATE_NOFIX:
-                    gps_acquirefix();
-                    blink_rate = 500;
-                    break;
-            }
+                blink_rate = BLINK_FAST;
+
+                // TODO: probably don't power on all the time, just on state transition
+                gps_poweron();
+                HAL_Delay(500);
+                gps_update_position();
+
+                if(fix_ok)
+                {
+                    // Disable GPS module
+                    gps_poweroff();
+
+                    // TODO: Set RTC from GPS time
+
+                    // TODO: Set RTC for countdown to next transmission timeslot!
 
-            uint8_t hour, minute, second;
-            gps_update_time(&hour, &minute, &second);
+                    // TODO: Set wspr countdown timer for this transmission!
+                    state = SYSTEM_WSPRTX;
+                }
+                else if(fix_timeout)
+                {
+                    // Flash error code and go to idle probably? or just try forever?
+                }
+
+            } break;
 
-            // EMZ TODO: this needs to trigger off of RTC minute, not GPS minute
-            // If last minute was odd and this minute is even (transition)
-//            if(lastMinute%2 == 1 && minute%2 == 0)
-//            {
-//                // Wait until the first second of the minute
-//                HAL_Delay(1000);
-//                wspr_transmit();
-//            }
+            
+            // Wait for wspr timeslot and start transmitting
+            case SYSTEM_WSPRTX:
+            {
+                // Wait for wspr countdown timer to expire and go to tx
+                if(timeout_expired)
+                {
+                    wspr_transmit();
+                }
 
-            lastMinute = minute;
-            last_wspr = HAL_GetTick();
+                // Schedule next wakeup (maybe 2mins prior ot timeslot if no osc trim)
+                // Next wakeup should enter SYSTEM_GPSACQ state...
+
+                state = SYSTEM_IDLE;
+
+            } break;
+
         }
 
+
         if(HAL_GetTick() - led_timer > blink_rate)
         {
             HAL_GPIO_TogglePin(LED_BLUE);
             led_timer = HAL_GetTick();
         }
-        if(HAL_GetTick() - last_gps > 10)
-        {
-            //gps_process();
-        	gps_update_position();
-            last_gps = HAL_GetTick();
-        }
 
-        //enter_sleep();
     }
 }
 
diff --git a/src/wspr.c b/src/wspr.c
--- a/src/wspr.c
+++ b/src/wspr.c
@@ -43,6 +43,9 @@ void wspr_init(void)
     HAL_NVIC_SetPriority(TIM1_BRK_UP_TRG_COM_IRQn, 0, 0);
     HAL_NVIC_EnableIRQ(TIM1_BRK_UP_TRG_COM_IRQn);
 
+    // Turn off ICs
+    HAL_GPIO_WritePin(OSC_NOTEN, 1);
+    HAL_GPIO_WritePin(TCXO_EN, 0);
 }
 
 // Do anything needed to prepare for sleep