Basic, read-only audiotrondHEADmain

Audiotrond exists and properly displays music being played through MPD.
The display includes title, artist, album, and progress bar, and text
scrolls if too long to fit on the screen. Backlight support exists; the
display backlight fades smoothly on and off when the music starts and
stops. After being stopped for a little while, audiotrond switches to a
clock. Currently, audiotrond lacks user interaction support, so it keeps
the keypad backlight off.

1 files changed, 128 insertions, 0 deletions

diff --git a/cfa635/decode.go b/cfa635/decode.go
new file mode 100644
index 0000000..dc77e03
--- /dev/null
+++ b/cfa635/decode.go
@@ -0,0 +1,128 @@
+// 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 (
+	"io"
+	"log"
+	"time"
+)
+
+const (
+	maxPacketBytes = 26
+
+	msgPacketFailed = "failed to read packet from CFA635:"
+	msgTimedOut     = "timed out"
+)
+
+var (
+	timeout = 250 * time.Millisecond // maximum response latency
+)
+
+// buffer copies bytes from an io.Reader into a channel, logging any errors as
+// it goes. It closes the channel when no more bytes are left or when it
+// receives on the done channel.
+func buffer(r io.ByteReader, w chan<- byte) {
+	defer close(w)
+	for {
+		b, err := r.ReadByte()
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			log.Print("failed to read byte from CFA635: ", err)
+			continue
+		}
+		w <- b
+	}
+}
+
+// decode reassembles bytes into packets, logging any errors as it goes.
+func decode(bytes <-chan byte, packets chan<- []byte) {
+	defer close(packets)
+Outer:
+	for {
+		p := make([]byte, 0, maxPacketBytes)
+
+		// Read packet type.
+		typ, ok := <-bytes
+		if !ok {
+			break
+		}
+		p = append(p, typ)
+
+		// The rest of the packet should come in fairly quickly.
+		timedout := time.After(timeout)
+
+		// Read packet length.
+		var length byte
+		select {
+		case <-timedout:
+			log.Print(msgPacketFailed, ' ', msgTimedOut)
+			continue
+
+		case length, ok = <-bytes:
+			if !ok {
+				break Outer
+			}
+			if length > 22 {
+				log.Print(msgPacketFailed, " got too-long data_length ", length)
+				continue
+			}
+			p = append(p, length)
+		}
+
+		// Read the data and CRC.
+		for i := 0; i < int(length)+2; i++ {
+			select {
+			case <-timedout:
+				log.Print(msgPacketFailed, ' ', msgTimedOut)
+				continue
+			case b, ok := <-bytes:
+				if !ok {
+					break Outer
+				}
+				p = append(p, b)
+			}
+		}
+
+		if p, ok = popCRC(p); !ok {
+			log.Printf("%s CRC failure\n", msgPacketFailed)
+			continue
+		}
+
+		// Save the packet.
+		packets <- p
+	}
+}
+
+// route splits a channel of packets into channels of reports and responses.
+func route(packets <-chan []byte, reports chan<- any, responses chan<- []byte) {
+	defer close(reports)
+	defer close(responses)
+	for p := range packets {
+		switch p[0] & 0b1100_0000 >> 6 {
+		case 0b10:
+			r, err := decodeReport(p)
+			if err != nil {
+				log.Print(err.Error())
+				continue
+			}
+			reports <- r
+		default:
+			responses <- p
+		}
+	}
+}