software: communication: Implement unslip()

This implements to decode the Serial Line Internet Protocol (SLIP). It
splits the continuous byte stream into frames. Based on these frames the
rest of the data link layer and upper layers can be implemented.

1 files changed, 63 insertions, 0 deletions

diff --git a/software/communication/data_link.go b/software/communication/data_link.go
new file mode 100644
index 0000000..d6e752d
--- /dev/null
+++ b/software/communication/data_link.go
@@ -0,0 +1,63 @@
+package communication
+
+const (
+	SLIP_END         = 0xC0
+	SLIP_ESC         = 0xDB
+	SLIP_ESC_END     = 0xDC
+	SLIP_ESC_ESC     = 0xDD
+	SLIP_MAX_PAYLOAD = 1500
+)
+
+type dataLink struct {
+	rx chan []byte
+}
+
+func newDataLink() dataLink {
+	dl := dataLink{}
+
+	dl.rx = make(chan []byte)
+
+	return dl
+}
+
+func (dl *dataLink) start(source chan byte) {
+	go dl.receive(source)
+}
+
+func (dl *dataLink) receive(source chan byte) {
+	for {
+		frame := unslip(source)
+		dl.rx <- frame
+	}
+}
+
+func unslip(source chan byte) []byte {
+	escaped := false
+	buffer := make([]byte, 0)
+
+	for {
+		octet := <-source
+		if escaped {
+			switch octet {
+			case SLIP_ESC_END:
+				buffer = append(buffer, SLIP_END)
+			case SLIP_ESC_ESC:
+				buffer = append(buffer, SLIP_ESC)
+			}
+		} else {
+			switch octet {
+			case SLIP_END:
+				break
+			case SLIP_ESC:
+				escaped = true
+				continue
+			default:
+				buffer = append(buffer, octet)
+				continue
+			}
+			break
+		}
+	}
+
+	return buffer
+}