diff --git a/Machines/Enterprise/Dave.cpp b/Machines/Enterprise/Dave.cpp
index 38a151d87..995ce29a5 100644
--- a/Machines/Enterprise/Dave.cpp
+++ b/Machines/Enterprise/Dave.cpp
@@ -235,22 +235,17 @@ void TimedInterruptSource::update_channel(int c, bool is_linked, int decrement)
 	if(channels_[c].sync) {
 		channels_[c].value = channels_[c].reload;
 	} else {
-		// TODO: the while loop below is far from efficient.
-
-		channels_[c].value -= decrement;
-		while(channels_[c].value < 0) {
-			channels_[c].value += channels_[c].reload + 1;
-
-			if(is_linked) {
-				if(channels_[c].level) {
-					interrupts_ |= uint8_t(Interrupt::VariableFrequency);
-				}
-				programmable_level_ = channels_[c].level;
+		if(decrement <= channels_[c].value) {
+			channels_[c].value -= decrement;
+		} else {
+			const int num_flips = (decrement - (channels_[c].value + 1)) / (channels_[c].reload + 1);
+			if(is_linked && num_flips + channels_[c].level >= 2) {
+				interrupts_ |= uint8_t(Interrupt::VariableFrequency);
 			}
-			channels_[c].level ^= true;
+			channels_[c].level ^= (num_flips & 1);
+			channels_[c].value = (decrement - (channels_[c].value + 1)) % (channels_[c].reload + 1);
 		}
 	}
-
 }
 
 void TimedInterruptSource::run_for(Cycles cycles) {
diff --git a/Machines/Enterprise/Dave.hpp b/Machines/Enterprise/Dave.hpp
index beb1db4fd..a280665af 100644
--- a/Machines/Enterprise/Dave.hpp
+++ b/Machines/Enterprise/Dave.hpp
@@ -136,15 +136,14 @@ class TimedInterruptSource {
 
 		Cycles one_hz_offset_ = clock_rate;
 
-		int programmable_offset_ = std::numeric_limits<int>::max();
-		bool programmable_level_ = false;
-
 		enum class InterruptRate {
 			OnekHz,
 			FiftyHz,
 			ToneGenerator0,
 			ToneGenerator1,
 		} rate_ = InterruptRate::OnekHz;
+		int programmable_offset_ = programmble_reload(InterruptRate::OnekHz);
+		bool programmable_level_ = false;
 
 		struct Channel {
 			int value = 100, reload = 100;