tester: add a mock for command-oriented i2c devices

tester/device.go

@@ -10,6 +10,9 @@ type I2CDevice interface {
 	// WriteRegister implements I2C.WriteRegister.
 	WriteRegister(r uint8, buf []byte) error
 
+	// Tx implements I2C.Tx
+	Tx(w, r []byte) error
+
 	// Addr returns the Device address.
 	Addr() uint8
 }

tester/device16.go

@@ -72,3 +72,9 @@ func (d *I2CDevice16) WriteRegister(r uint8, buf []byte) error {
 
 	return nil
 }
+
+// Tx implements I2C.Tx.
+func (bus *I2CDevice16) Tx(w, r []byte) error {
+	// TODO: implement this
+	return nil
+}

tester/device8.go

@@ -53,6 +53,12 @@ func (d *I2CDevice8) WriteRegister(r uint8, buf []byte) error {
 	return nil
 }
 
+// Tx implements I2C.Tx.
+func (bus *I2CDevice8) Tx(w, r []byte) error {
+	// TODO: implement this
+	return nil
+}
+
 // assertRegisterRange asserts that reading or writing the given
 // register and subsequent registers is in range of the available registers.
 func (d *I2CDevice8) assertRegisterRange(r uint8, buf []byte) {

tester/devicecmd.go

@@ -0,0 +1,126 @@
+package tester
+
+// Cmd represents a command sent via I2C to a device.
+//
+// A command matches when (Command & Mask) == (Data & Mask).  If
+// a command is recognized, Response bytes is returned.
+type Cmd struct {
+	Command     []byte
+	Mask        []byte
+	Response    []byte
+	Invocations int
+}
+
+// I2CDeviceCmd represents a mock I2C device that does not
+// have 'registers', but has a command/response model.
+//
+// Commands and canned responses are pre-loaded into the
+// Commands member.  For each command the mock receives it
+// will lookup the command and return the corresponding
+// canned response.
+type I2CDeviceCmd struct {
+	c Failer
+
+	// addr is the i2c device address.
+	addr uint8
+
+	// Commands are the commands the device recognizes and responds to.
+	Commands map[uint8]*Cmd
+
+	// Command response that is pending (used with a command is split over)
+	// two transactions
+	pendingResponse []byte
+
+	// If Err is non-nil, it will be returned as the error from the
+	// I2C methods.
+	Err error
+}
+
+// NewI2CDeviceCmd returns a new mock I2C device.
+func NewI2CDeviceCmd(c Failer, addr uint8) *I2CDeviceCmd {
+	return &I2CDeviceCmd{
+		c:    c,
+		addr: addr,
+	}
+}
+
+// Addr returns the Device address.
+func (d *I2CDeviceCmd) Addr() uint8 {
+	return d.addr
+}
+
+// ReadRegister implements I2C.ReadRegister.
+func (d *I2CDeviceCmd) ReadRegister(r uint8, buf []byte) error {
+	if d.Err != nil {
+		return d.Err
+	}
+
+	return nil
+}
+
+// WriteRegister implements I2C.WriteRegister.
+func (d *I2CDeviceCmd) WriteRegister(r uint8, buf []byte) error {
+	if d.Err != nil {
+		return d.Err
+	}
+
+	return nil
+}
+
+// Tx implements I2C.Tx.
+func (d *I2CDeviceCmd) Tx(w, r []byte) error {
+	if d.Err != nil {
+		return d.Err
+	}
+
+	if len(w) == 0 && len(d.pendingResponse) != 0 {
+		return d.respond(r)
+	}
+
+	cmd := d.FindCommand(w)
+	if cmd == nil {
+		d.c.Fatalf("command [%#x] not identified", w)
+		return nil
+	}
+
+	cmd.Invocations++
+	d.pendingResponse = cmd.Response
+	return d.respond(r)
+}
+
+func (d *I2CDeviceCmd) FindCommand(command []byte) *Cmd {
+	for _, c := range d.Commands {
+		if len(c.Command) > len(command) {
+			continue
+		}
+
+		match := true
+		for i := 0; i < len(c.Command); i++ {
+			mask := c.Mask[i]
+			if (c.Command[i] & mask) != (command[i] & mask) {
+				match = false
+				break
+			}
+		}
+
+		if match {
+			return c
+		}
+	}
+
+	return nil
+}
+
+func (d *I2CDeviceCmd) respond(r []byte) error {
+	if len(r) > len(d.pendingResponse) {
+		d.c.Fatalf("read too large (expected: <= %#x, got: %#x)",
+			len(d.pendingResponse), len(r))
+	}
+
+	if len(r) > 0 {
+		copy(r, d.pendingResponse[:len(r)])
+		d.pendingResponse = nil
+	}
+
+	return nil
+}

tester/i2c.go

@@ -48,8 +48,7 @@ func (bus *I2CBus) WriteRegister(addr uint8, r uint8, buf []byte) error {
 
 // Tx implements I2C.Tx.
 func (bus *I2CBus) Tx(addr uint16, w, r []byte) error {
-	// TODO: implement this
+	return bus.FindDevice(uint8(addr)).Tx(w, r)
-	return nil
 }
 
 // FindDevice returns the device with the given address.