diff --git a/easystepper/easystepper.go b/easystepper/easystepper.go
index b6b93f830..56711dda9 100644
--- a/easystepper/easystepper.go
+++ b/easystepper/easystepper.go
@@ -7,6 +7,10 @@ import (
 	"time"
 )
 
+var (
+	ErrRPM = errors.New("rpm must be greater than zero")
+)
+
 // StepMode determines the coil sequence used to perform a single step
 type StepMode uint8
 
@@ -55,11 +59,58 @@ type Device struct {
 	stepDelay  time.Duration
 	stepNumber uint8
 	stepMode   StepMode
+
+	// stepCount is the number of steps for one full revolution.
+	// SetRPM needs it to calculate a new stepDelay.
+	stepCount uint
+
+	// remainingSteps is how many steps MoveAsync has left to do.
+	remainingSteps uint32
+
+	// direction is true to move forward and false to move backward.
+	direction bool
+
+	// moving is true when the motor has movement scheduled.
+	moving bool
+
+	// continuous is true to move until Stop. If it is false, movement
+	// stops when remainingSteps is zero.
+	continuous bool
+
+	// nextStep is the time of the next step. Update uses it to return
+	// immediately when no step is necessary.
+	nextStep time.Time
 }
 
 // DualDevice holds information for controlling 2 motors
 type DualDevice struct {
 	devices [2]*Device
+
+	// moving is true when a non blocking dual movement is active.
+	moving bool
+
+	// continuous is true to move both motors until Stop.
+	continuous bool
+
+	// directions is the direction of each motor.
+	directions [2]bool
+
+	// totalSteps is the number of steps requested for each motor.
+	// Update needs it to divide the steps of the slower motor.
+	totalSteps [2]uint32
+
+	// completedSteps is the number of steps each motor has done.
+	completedSteps [2]uint32
+
+	// primary is the motor with the most steps. It controls the
+	// timing of a coordinated MoveAsync.
+	primary uint8
+
+	// secondary is the other motor.
+	secondary uint8
+
+	// nextStep is the time of the next coordinated step.
+	nextStep time.Time
 }
 
 // New returns a new single easystepper driver given a DeviceConfig
@@ -71,6 +122,7 @@ func New(config DeviceConfig) (*Device, error) {
 		pins:      [4]machine.Pin{config.Pin1, config.Pin2, config.Pin3, config.Pin4},
 		stepDelay: time.Second * 60 / time.Duration((config.StepCount * config.RPM)),
 		stepMode:  config.Mode,
+		stepCount: config.StepCount,
 	}, nil
 }
 
@@ -107,62 +159,248 @@ func (d *DualDevice) Configure() {
 	d.devices[1].Configure()
 }
 
-// Move rotates the motor the number of given steps
-// (negative steps will rotate it the opposite direction)
+// Move rotates the motor the number of given steps and waits until the
+// movement is complete. Negative steps rotate it the opposite direction.
 func (d *Device) Move(steps int32) {
+	if steps == 0 {
+		return
+	}
 	direction := steps > 0
 	if steps < 0 {
 		steps = -steps
 	}
-	steps += int32(d.stepNumber)
-	var s int32
-	d.stepMotor(d.stepNumber)
-	for s = int32(d.stepNumber); s < steps; s++ {
+	for i := int32(0); i < steps; i++ {
+		d.step(direction)
 		time.Sleep(d.stepDelay)
-		d.moveDirectionSteps(direction, s)
 	}
 }
 
-// Off turns off all motor pins
+// MoveAsync schedules a number of steps and returns immediately. Negative
+// steps move backward. You must call Update to make the motor move.
+func (d *Device) MoveAsync(steps int32) {
+	if steps == 0 {
+		return
+	}
+	d.continuous = false
+	d.direction = steps > 0
+	if steps < 0 {
+		steps = -steps
+	}
+	d.remainingSteps = uint32(steps)
+	d.moving = true
+	d.nextStep = time.Now()
+}
+
+// Start moves the motor until Stop and returns immediately. You must call
+// Update to make the motor move.
+func (d *Device) Start(direction bool) {
+	d.direction = direction
+	d.continuous = true
+	d.moving = true
+	d.nextStep = time.Now()
+}
+
+// Update does one step if a step is due. It does not block. Call it
+// frequently from the main loop.
+func (d *Device) Update() {
+	if !d.moving {
+		return
+	}
+	now := time.Now()
+	if now.Before(d.nextStep) {
+		return
+	}
+	d.step(d.direction)
+	if !d.continuous {
+		d.remainingSteps--
+		if d.remainingSteps == 0 {
+			d.moving = false
+			return
+		}
+	}
+	d.nextStep = schedule(d.nextStep, now, d.stepDelay)
+}
+
+// schedule gives the time of the next step. It adds the delay to the last
+// time to prevent drift, but starts from now if the caller is very late.
+func schedule(last, now time.Time, delay time.Duration) time.Time {
+	next := last.Add(delay)
+	if next.Before(now) {
+		return now.Add(delay)
+	}
+	return next
+}
+
+// Stop ends the movement from MoveAsync or Start. The coils stay on, so the
+// motor holds its position. Use Off to also remove power from the coils.
+func (d *Device) Stop() {
+	d.moving = false
+	d.continuous = false
+	d.remainingSteps = 0
+}
+
+// IsMoving tells you if the motor has an active movement.
+func (d *Device) IsMoving() bool {
+	return d.moving
+}
+
+// Off turns off all motor pins. This removes power from the coils, so the
+// motor does not hold its position.
 func (d *Device) Off() {
 	for _, pin := range d.pins {
 		pin.Low()
 	}
 }
 
+// SetRPM changes the speed of the motor. You can call it while the motor
+// moves. The new speed applies to the steps that follow.
+func (d *Device) SetRPM(rpm uint) error {
+	if rpm == 0 {
+		return ErrRPM
+	}
+	d.stepDelay = time.Second * 60 / time.Duration(d.stepCount*rpm)
+	return nil
+}
+
 // Move rotates the motors the number of given steps
 // (negative steps will rotate it the opposite direction)
 func (d *DualDevice) Move(stepsA, stepsB int32) {
-	min := uint8(1)
-	max := uint8(0)
-	var directions [2]bool
-	var minStep int32
+	if stepsA == 0 && stepsB == 0 {
+		return
+	}
+	primary, secondary, directions, totals := d.plan(stepsA, stepsB)
+	var completed [2]uint32
+
+	for completed[primary] < totals[primary] {
+		d.devices[primary].step(directions[primary])
+		completed[primary]++
+
+		if completed[secondary] < share(completed[primary], totals, primary, secondary) {
+			d.devices[secondary].step(directions[secondary])
+			completed[secondary]++
+		}
+		time.Sleep(d.devices[primary].stepDelay)
+	}
+}
 
-	directions[0] = stepsA > 0
-	directions[1] = stepsB > 0
+// plan gives the motor with the most steps, the other motor, the direction
+// of each motor, and the number of steps each motor must do.
+func (d *DualDevice) plan(stepsA, stepsB int32) (uint8, uint8, [2]bool, [2]uint32) {
+	directions := [2]bool{stepsA > 0, stepsB > 0}
 	if stepsA < 0 {
 		stepsA = -stepsA
 	}
 	if stepsB < 0 {
 		stepsB = -stepsB
 	}
+	primary, secondary := uint8(0), uint8(1)
 	if stepsB > stepsA {
-		stepsA, stepsB = stepsB, stepsA
-		max, min = min, max
-	}
-	d.devices[0].stepMotor(d.devices[0].stepNumber)
-	d.devices[1].stepMotor(d.devices[1].stepNumber)
-	stepsA += int32(d.devices[max].stepNumber)
-	minStep = int32(d.devices[min].stepNumber)
-	for s := int32(d.devices[max].stepNumber); s < stepsA; s++ {
-		time.Sleep(d.devices[0].stepDelay)
-		d.devices[max].moveDirectionSteps(directions[max], s)
-
-		if ((s * stepsB) / stepsA) > minStep {
-			minStep++
-			d.devices[min].moveDirectionSteps(directions[min], minStep)
-		}
+		primary, secondary = 1, 0
+	}
+	return primary, secondary, directions, [2]uint32{uint32(stepsA), uint32(stepsB)}
+}
+
+// share gives the steps the slower motor must have done. It needs 64 bits
+// because two step counts near 65535 overflow a uint32.
+func share(done uint32, totals [2]uint32, primary, secondary uint8) uint32 {
+	return uint32(uint64(done) * uint64(totals[secondary]) / uint64(totals[primary]))
+}
+
+// MoveAsync starts a movement of both motors and returns immediately. Both
+// motors stop together, as with Move. Call Update to make them move.
+func (d *DualDevice) MoveAsync(stepsA, stepsB int32) {
+	if stepsA == 0 && stepsB == 0 {
+		return
+	}
+	// Update drives each motor directly in this mode, so cancel any
+	// movement that Start gave to the two motors.
+	d.devices[0].Stop()
+	d.devices[1].Stop()
+
+	d.primary, d.secondary, d.directions, d.totalSteps = d.plan(stepsA, stepsB)
+	d.completedSteps[0] = 0
+	d.completedSteps[1] = 0
+	d.continuous = false
+	d.moving = true
+	d.nextStep = time.Now()
+}
+
+// SetRPM changes the speed of both motors.
+func (d *DualDevice) SetRPM(rpm uint) error {
+	return d.SetRPMs(rpm, rpm)
+}
+
+// SetRPMs changes the speed of each motor. Different speeds turn a robot
+// that has one motor on each wheel.
+func (d *DualDevice) SetRPMs(rpmA, rpmB uint) error {
+	if err := d.devices[0].SetRPM(rpmA); err != nil {
+		return err
 	}
+	return d.devices[1].SetRPM(rpmB)
+}
+
+// Update does the next step of a DualDevice movement if a step is due. It
+// does not block. Call it frequently from the main loop.
+func (d *DualDevice) Update() {
+	if !d.moving {
+		return
+	}
+
+	// After Start each motor keeps its own speed and its own timing.
+	if d.continuous {
+		d.devices[0].Update()
+		d.devices[1].Update()
+		return
+	}
+
+	now := time.Now()
+	if now.Before(d.nextStep) {
+		return
+	}
+
+	primary := d.primary
+	secondary := d.secondary
+
+	d.devices[primary].step(d.directions[primary])
+	d.completedSteps[primary]++
+
+	if d.completedSteps[secondary] < share(d.completedSteps[primary], d.totalSteps, primary, secondary) {
+		d.devices[secondary].step(d.directions[secondary])
+		d.completedSteps[secondary]++
+	}
+
+	if d.completedSteps[primary] >= d.totalSteps[primary] {
+		d.moving = false
+		return
+	}
+
+	d.nextStep = schedule(d.nextStep, now, d.devices[primary].stepDelay)
+}
+
+// Start moves both motors until Stop and returns immediately. Each motor
+// keeps its own speed from SetRPMs. Call Update to make them move.
+func (d *DualDevice) Start(directionA, directionB bool) {
+	d.continuous = true
+	d.moving = true
+	d.devices[0].Start(directionA)
+	d.devices[1].Start(directionB)
+}
+
+// Stop ends all movement. The coils stay on, so the motors hold their
+// position. Use Off to also remove power from the coils.
+func (d *DualDevice) Stop() {
+	d.moving = false
+	d.continuous = false
+	d.devices[0].Stop()
+	d.devices[1].Stop()
+}
+
+// IsMoving tells you if one of the motors has an active movement.
+func (d *DualDevice) IsMoving() bool {
+	if d.continuous {
+		return d.devices[0].IsMoving() || d.devices[1].IsMoving()
+	}
+	return d.moving
 }
 
 // Off turns off all motor pins
@@ -171,6 +409,21 @@ func (d *DualDevice) Off() {
 	d.devices[1].Off()
 }
 
+// step moves the motor one step. It does not wait, so Move and Update can
+// both use it. Forward in 4 step mode gives 0, 1, 2, 3, 0, 1, and backward
+// gives 0, 3, 2, 1, 0, 3.
+func (d *Device) step(direction bool) {
+	// Length of the coil sequence, which is 4 or 8. This is not the
+	// stepCount field, which is the steps for one revolution.
+	seq := uint8(d.stepMode.stepCount())
+	if direction {
+		d.stepNumber = (d.stepNumber + 1) % seq
+	} else {
+		d.stepNumber = (d.stepNumber + seq - 1) % seq
+	}
+	d.stepMotor(d.stepNumber)
+}
+
 // stepMotor changes the pins' state to the correct step
 func (d *Device) stepMotor(step uint8) {
 	switch d.stepMode {
@@ -260,17 +513,3 @@ func (d *Device) stepMotor8(step uint8) {
 	}
 	d.stepNumber = step
 }
-
-// moveDirectionSteps uses the direction to calculate the correct step and change the motor to it.
-// Direction true:  (4-step mode) 0, 1, 2, 3, 0, 1, 2, ...
-// Direction false: (4-step mode) 0, 3, 2, 1, 0, 3, 2, ...
-// Direction true:  (8-step mode) 0, 1, 2, 3, 4, 5, 6, 7, 0, 1, 2, ...
-// Direction false: (8-step mode) 0, 7, 6, 5, 4, 3, 2, 1, 0, 7, 6, ...
-func (d *Device) moveDirectionSteps(direction bool, step int32) {
-	modulus := int32(d.stepMode.stepCount())
-	if direction {
-		d.stepMotor(uint8(step % modulus))
-	} else {
-		d.stepMotor(uint8(((-step % modulus) + modulus) % modulus))
-	}
-}
diff --git a/examples/easystepper/async/main.go b/examples/easystepper/async/main.go
new file mode 100644
index 000000000..3a8945ba1
--- /dev/null
+++ b/examples/easystepper/async/main.go
@@ -0,0 +1,64 @@
+package main
+
+import (
+	"machine"
+	"time"
+
+	"tinygo.org/x/drivers/easystepper"
+)
+
+const stepsPerTurn = 2048
+
+func main() {
+	motor, err := easystepper.New(easystepper.DeviceConfig{
+		Pin1: machine.P13, Pin2: machine.P15, Pin3: machine.P14, Pin4: machine.P16,
+		StepCount: stepsPerTurn, RPM: 4, Mode: easystepper.ModeFour,
+	})
+	if err != nil {
+		println("motor init failed:", err.Error())
+		return
+	}
+	motor.Configure()
+
+	for {
+		// MoveAsync returns at once. Update does the steps, so the loop is
+		// free for other work.
+		println("one turn, faster every 700ms")
+		motor.MoveAsync(stepsPerTurn)
+
+		rpm := uint(4)
+		loops := 0
+		change := time.Now().Add(700 * time.Millisecond)
+
+		for motor.IsMoving() {
+			motor.Update()
+
+			// Your own work goes here. The motor does not stop it.
+			loops++
+
+			// SetRPM works while the motor turns. Move cannot do this.
+			if rpm < 16 && time.Now().After(change) {
+				rpm += 2
+				motor.SetRPM(rpm)
+				println("rpm:", rpm)
+				change = time.Now().Add(700 * time.Millisecond)
+			}
+		}
+		println("loop ran", loops, "times while the motor turned")
+		motor.Off()
+		time.Sleep(time.Second)
+
+		// Start turns until Stop. Update still does the steps.
+		println("continuous for 3s, then stop")
+		motor.SetRPM(10)
+		motor.Start(false)
+
+		end := time.Now().Add(3 * time.Second)
+		for time.Now().Before(end) {
+			motor.Update()
+		}
+		motor.Stop()
+		motor.Off()
+		time.Sleep(time.Second)
+	}
+}
diff --git a/smoketest.sh b/smoketest.sh
index 3d20b67d8..1959e484b 100755
--- a/smoketest.sh
+++ b/smoketest.sh
@@ -26,6 +26,7 @@ tinygo build -size short -o ./build/test.hex -target=bluepill ./examples/ds1307/
 tinygo build -size short -o ./build/test.hex -target=itsybitsy-m0 ./examples/ds3231/alarms/main.go
 tinygo build -size short -o ./build/test.hex -target=itsybitsy-m0 ./examples/ds3231/basic/main.go
 tinygo build -size short -o ./build/test.hex -target=microbit ./examples/easystepper/main.go
+tinygo build -size short -o ./build/test.hex -target=microbit ./examples/easystepper/async/main.go
 tinygo build -size short -o ./build/test.hex -target=itsybitsy-m0 ./examples/flash/console/spi
 tinygo build -size short -o ./build/test.hex -target=pyportal ./examples/flash/console/qspi
 tinygo build -size short -o ./build/test.hex -target=microbit ./examples/gc9a01/main.go