diff --git a/Machines/AtariST/AtariST.cpp b/Machines/AtariST/AtariST.cpp
index 87821642d..9edf3b0dd 100644
--- a/Machines/AtariST/AtariST.cpp
+++ b/Machines/AtariST/AtariST.cpp
@@ -47,7 +47,8 @@ class ConcreteMachine:
 	public Motorola::MFP68901::MFP68901::InterruptDelegate,
 	public DMAController::InterruptDelegate,
 	public MouseMachine::Machine,
-	public KeyboardMachine::MappedMachine {
+	public KeyboardMachine::MappedMachine,
+	public GI::AY38910::PortHandler {
 	public:
 		ConcreteMachine(const Target &target, const ROMMachine::ROMFetcher &rom_fetcher) :
 			mc68000_(*this),
@@ -99,6 +100,7 @@ class ConcreteMachine:
 
 			mfp_->set_interrupt_delegate(this);
 			dma_->set_interrupt_delegate(this);
+			ay_.set_port_handler(this);
 
 			set_gpip_input();
 		}
@@ -235,18 +237,6 @@ class ConcreteMachine:
 								ay_.set_data_input(cycle.value8_high());
 								ay_.set_control_lines(GI::AY38910::ControlLines(0));
 							}
-
-							/*
-								TODO: Port A:
-									b7: reserved
-									b6: "freely usable output (monitor jack)"
-									b5: centronics strobe
-									b4: RS-232 DTR output
-									b3: RS-232 RTS output
-									b2: select floppy drive 1
-									b1: select floppy drive 0
-									b0: "page choice signal for double-sided floppy drive"
-							*/
 						return HalfCycles(2);
 
 						// The MFP block:
@@ -501,6 +491,25 @@ class ConcreteMachine:
 			return &keyboard_mapper_;
 		}
 
+		// MARK: - AYPortHandler
+		void set_port_output(bool port_b, uint8_t value) final {
+			if(port_b) {
+				// TODO: ?
+			} else {
+				/*
+					TODO: Port A:
+						b7: reserved
+						b6: "freely usable output (monitor jack)"
+						b5: centronics strobe
+						b4: RS-232 DTR output
+						b3: RS-232 RTS output
+						b2: select floppy drive 1
+						b1: select floppy drive 0
+						b0: "page choice signal for double-sided floppy drive"
+				*/
+				dma_->set_floppy_drive_selection(value & 2, value & 4, value & 1);
+			}
+		}
 };
 
 }
diff --git a/Machines/AtariST/DMAController.cpp b/Machines/AtariST/DMAController.cpp
index 46ba8865e..2bb64a9c3 100644
--- a/Machines/AtariST/DMAController.cpp
+++ b/Machines/AtariST/DMAController.cpp
@@ -81,6 +81,10 @@ void DMAController::write(int address, uint16_t value) {
 	}
 }
 
+void DMAController::set_floppy_drive_selection(bool drive1, bool drive2, bool side2) {
+	fdc_.set_floppy_drive_selection(drive1, drive2, side2);
+}
+
 void DMAController::run_for(HalfCycles duration) {
 	running_time_ += duration;
 	fdc_.run_for(duration.flush<Cycles>());
diff --git a/Machines/AtariST/DMAController.hpp b/Machines/AtariST/DMAController.hpp
index cbedc18ed..6e4194537 100644
--- a/Machines/AtariST/DMAController.hpp
+++ b/Machines/AtariST/DMAController.hpp
@@ -29,6 +29,8 @@ class DMAController: public WD::WD1770::Delegate, public ClockingHint::Source, p
 
 		bool get_interrupt_line();
 
+		void set_floppy_drive_selection(bool drive1, bool drive2, bool side2);
+
 		struct InterruptDelegate {
 			virtual void dma_controller_did_change_interrupt_status(DMAController *) = 0;
 		};
@@ -51,6 +53,18 @@ class DMAController: public WD::WD1770::Delegate, public ClockingHint::Source, p
 				drives_[1]->set_motor_on(motor_on);
 			}
 
+			void set_floppy_drive_selection(bool drive1, bool drive2, bool side2) {
+				// TODO: handle no drives and/or both drives selected.
+				if(drive1) {
+					set_drive(drives_[0]);
+				} else {
+					set_drive(drives_[1]);
+				}
+
+				drives_[0]->set_head(side2);
+				drives_[1]->set_head(side2);
+			}
+
 			std::vector<std::shared_ptr<Storage::Disk::Drive>> drives_;
 		} fdc_;