1 files changed, 109 insertions, 0 deletions
diff --git a/cfa635/report.go b/cfa635/report.go
new file mode 100644
index 0000000..84541bc
--- /dev/null
+++ b/cfa635/report.go
@@ -0,0 +1,109 @@
+// Copyright 2022 Benjamin Barenblat
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may not
+// use this file except in compliance with the License. You may obtain a copy of
+// the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+// License for the specific language governing permissions and limitations under
+// the License.
+
+package cfa635
+
+import (
+	"encoding/binary"
+	"errors"
+)
+
+var (
+	errUnknownReportType = errors.New("failed to read report: unknown type")
+	errUnknownKey        = errors.New("failed to read key activity report: unknown key")
+	errFBSCAB            = errors.New("failed to read fan speed report: FBSCAB module disconnected")
+	errDOW               = errors.New("failed to read temperature report: DOW sensor error")
+)
+
+// KeyActivity is a report that a key has been pressed or released.
+type KeyActivity struct {
+	K       Key
+	Pressed bool
+}
+
+// Key represents a button on the CFA635.
+type Key int
+
+const (
+	_ Key = iota
+	UpButton
+	DownButton
+	LeftButton
+	RightButton
+	EnterButton
+	ExitButton
+)
+
+// FanSpeed is a report on the speed of a system fan.
+type FanSpeed struct {
+	N          int
+	TachCycles int
+	TimerTicks int
+}
+
+// Temperature is a report on the system temperature.
+type Temperature struct {
+	N       int // Sensor number.
+	Celsius float64
+}
+
+// decodeReport converts a packet into either a *KeyActivity, a *FanSpeed, or a
+// *Temperature, depending on the packet's type tag.
+func decodeReport(p []byte) (any, error) {
+	switch p[0] {
+	case 0x80:
+		return decodeKeyActivity(p[2])
+	case 0x81:
+		return decodeFanSpeed(p[2:6])
+	case 0x82:
+		return decodeTemperature(p[2:6])
+	default:
+		return nil, errUnknownReportType
+	}
+}
+
+// decodeKeyActivity converts the data byte from a key activity report to a
+// KeyActivity.
+func decodeKeyActivity(b byte) (*KeyActivity, error) {
+	if b == 0 || b > 12 {
+		return nil, errUnknownKey
+	}
+
+	var a KeyActivity
+	if b < 7 {
+		a.Pressed = true
+	} else {
+		b -= 6
+	}
+	a.K = Key(b)
+	return &a, nil
+}
+
+// decodeFanSpeed converts the data part of a fan speed report packet to a
+// FanSpeed.
+func decodeFanSpeed(b []byte) (*FanSpeed, error) {
+	if b[1] == 0 && b[2] == 0 && b[3] == 0 {
+		return nil, errFBSCAB
+	}
+	return &FanSpeed{int(b[0]), int(b[1]), int(binary.BigEndian.Uint16(b[2:4]))}, nil
+}
+
+// decodeTemperature converts the data part of a temperature report packet to a
+// Temperature.
+func decodeTemperature(b []byte) (*Temperature, error) {
+	if b[3] == 0 {
+		return nil, errDOW
+	}
+	return &Temperature{int(b[0]), float64(binary.BigEndian.Uint16(b[1:3])) / 16}, nil
+}