added options and example

README.md

@@ -1,2 +1,35 @@
 Go port of the POCSAG::Encode Perl module.
 
+Example usage
+```
+package main
+
+import (
+	"fmt"
+	"log"
+
+	"github.com/kgolding/go-pocsagencode"
+)
+
+func main() {
+	messages := []*pocsagencode.Message{
+		&pocsagencode.Message{1300100, "Hello Pager!"},
+	}
+
+	for i := 0; i < 50; i++ {
+		addr := uint32(1200000 + i*100)
+		messages = append(messages, &pocsagencode.Message{addr, fmt.Sprintf("Hello pager number %d", addr)})
+	}
+
+	log.Println("Sending", len(messages), "messages")
+	var burst pocsagencode.Burst
+	for len(messages) > 0 {
+		burst, messages = pocsagencode.Generate(messages)
+		// Options can be set as below for MaxLen and PreambleBits
+		// burst, messages = pocsagencode.Generate(messages, pocsagencode.OptionPreambleBits(250))
+		log.Println("Burst", burst.String())
+		// Send Burst to the FSK modem here...
+	}
+	log.Println("Done")
+}
+```

example/pocsag-example.go

@@ -0,0 +1,30 @@
+package main
+
+import (
+	"fmt"
+	"log"
+
+	"github.com/kgolding/go-pocsagencode"
+)
+
+func main() {
+	messages := []*pocsagencode.Message{
+		&pocsagencode.Message{1300100, "Hello Pager!"},
+	}
+
+	for i := 0; i < 50; i++ {
+		addr := uint32(1200000 + i*100)
+		messages = append(messages, &pocsagencode.Message{addr, fmt.Sprintf("Hello pager number %d", addr)})
+	}
+
+	log.Println("Sending", len(messages), "messages")
+	var burst pocsagencode.Burst
+	for len(messages) > 0 {
+		burst, messages = pocsagencode.Generate(messages)
+		// Options can be set as below for MaxLen and PreambleBits
+		// burst, messages = pocsagencode.Generate(messages, pocsagencode.OptionPreambleBits(250))
+		log.Println("Burst", burst.String())
+		// Send Burst to the FSK modem here...
+	}
+	log.Println("Done")
+}

helpers.go

@@ -0,0 +1,40 @@
+package pocsagencode
+
+import (
+	"encoding/binary"
+	"fmt"
+)
+
+type Burst []uint32
+
+// String return a formated multiline string with the
+func (b Burst) String() string {
+	s := ""
+	preambleCount := 0
+	preambleOver := false
+	for _, w := range b {
+		if !preambleOver {
+			if w == pocsagPreambleWord {
+				preambleCount++
+				continue
+			} else {
+				s += fmt.Sprintf("[%d bits of 1010101010... (0xAA) preamble] ", preambleCount*32)
+				preambleOver = true
+			}
+		}
+		if w == pocsagFrameSyncWord {
+			s += "[Batch start/sync] "
+		}
+		s += fmt.Sprintf("%X ", w)
+	}
+	return s
+}
+
+// Bytes returns a []byte
+func (b Burst) Bytes() []byte {
+	buf := make([]byte, len(b)*4)
+	for i, w := range b {
+		binary.BigEndian.PutUint32(buf[i*4:], w)
+	}
+	return buf
+}

options.go

@@ -0,0 +1,20 @@
+package pocsagencode
+
+type Options struct {
+	MaxLen       int
+	PreambleBits int
+}
+
+type OptionFn func(*Options)
+
+func OptionMaxLen(v int) OptionFn {
+	return func(o *Options) {
+		o.MaxLen = v
+	}
+}
+
+func OptionPreambleBits(v int) OptionFn {
+	return func(o *Options) {
+		o.PreambleBits = v
+	}
+}

pocsag-encode.go

@@ -120,8 +120,8 @@ func reverseBits(in byte) byte {
 }
 
 // appendContentText appends text message content to the transmission blob
-func appendContentText(content string) (int, []uint32) {
+func appendContentText(content string) (int, Burst) {
-	out := make([]uint32, 0)
+	out := make(Burst, 0)
 	debugf("appendContentText: %s", content)
 
 	bitpos := 0
@@ -186,7 +186,7 @@ func appendContentText(content string) (int, []uint32) {
 }
 
 // appendMessage appends a single message to the end of the transmission blob.
-func appendMessage(startpos int, msg *Message) (int, []uint32) {
+func appendMessage(startpos int, msg *Message) (int, Burst) {
 	// expand the parameters of the message
 	addr := msg.Addr
 	function := byte(0)
@@ -202,7 +202,7 @@ func appendMessage(startpos int, msg *Message) (int, []uint32) {
 	debugf("  frame_addr is %d, current position %d", frameAddr, startpos)
 
 	// append idle codewords, until we're in the right frame for this address
-	tx := make([]uint32, 0)
+	tx := make(Burst, 0)
 	pos := 0
 	for uint32(startpos+pos)%16 != frameAddrCw {
 		debugf("   inserting IDLE codewords in position %d (%d)", startpos+pos, (startpos+pos)%16)
@@ -228,8 +228,8 @@ func appendMessage(startpos int, msg *Message) (int, []uint32) {
 
 // insertSCS inserts Synchronisation Codewords before every 8 POCSAG frames
 // (frame is SC+ 64 bytes of address and message codewords)
-func insertSCS(tx []uint32) []uint32 {
+func insertSCS(tx Burst) Burst {
-	out := make([]uint32, 0)
+	out := make(Burst, 0)
 
 	// each batch is SC + 8 frames, each frame is 2 codewords,
 	// each codeword is 32 bits, so we must insert an SC
@@ -294,9 +294,17 @@ func selectMsg(pos int, msgListRef []*Message) int {
 // any messages which did not fit in the transmission, given the maximum
 // transmission length (in bytes) given in the first parameter. They can be passed
 // in the next Generate() call and sent in the next brrraaaap.
-func Generate(maxLen int, preambleBits int, messages []*Message) ([]uint32, []*Message) {
+func Generate(messages []*Message, optionFns ...OptionFn) (Burst, []*Message) {
-	txWithoutScs := make([]uint32, 0)
+	options := &Options{
-	debugf("generate_transmission, maxlen: %d", maxLen)
+		MaxLen:       3000,
+		PreambleBits: 576,
+	}
+	for _, opt := range optionFns {
+		opt(options)
+	}
+
+	txWithoutScs := make(Burst, 0)
+	debugf("generate_transmission, maxlen: %d", options.MaxLen)
 
 	pos := 0
 	for len(messages) > 0 {
@@ -315,11 +323,11 @@ func Generate(maxLen int, preambleBits int, messages []*Message) ([]uint32, []*M
 		nextLenBytes := nextLen * 4
 		debugf("after this message of %d codewords, burst will be %d codewords and %d bytes long\n", appendLen, nextLen, nextLenBytes)
 
-		if nextLenBytes > maxLen {
+		if nextLenBytes > int(options.MaxLen) {
 			if pos == 0 {
-				debugf("burst would become too large (%d > %d) with first message alone - discarding!", nextLenBytes, maxLen)
+				debugf("burst would become too large (%d > %d) with first message alone - discarding!", nextLenBytes, options.MaxLen)
 			} else {
-				debugf("burst would become too large (%d > %d) - returning msg in queue", nextLenBytes, maxLen)
+				debugf("burst would become too large (%d > %d) - returning msg in queue", nextLenBytes, options.MaxLen)
 				messages = append([]*Message{msg}, messages...)
 				break
 			}
@@ -331,7 +339,7 @@ func Generate(maxLen int, preambleBits int, messages []*Message) ([]uint32, []*M
 
 	// if the burst is empty, return it as completely empty
 	if pos == 0 {
-		return []uint32{}, messages
+		return Burst{}, messages
 	}
 
 	// append a couple of IDLE codewords, otherwise many pagers will
@@ -348,12 +356,12 @@ func Generate(maxLen int, preambleBits int, messages []*Message) ([]uint32, []*M
 	burstLen = len(burst)
 	debugf("transmission with SCs: %d bytes, %d codewords\n%X\n", burstLen*4, burstLen, burst)
 
-	if preambleBits > 0 {
+	if options.PreambleBits > 0 {
-		preambleWords := preambleBits / 32
+		preambleWords := options.PreambleBits / 32
-		if preambleBits%32 > 0 {
+		if options.PreambleBits%32 > 0 {
 			preambleWords++
 		}
-		preamble := make([]uint32, preambleWords)
+		preamble := make(Burst, preambleWords)
 		for i := range preamble {
 			preamble[i] = pocsagPreambleWord
 		}

pocsagencode_test.go

@@ -1,21 +1,19 @@
 package pocsagencode
 
 import (
-	// "log"
-	// "os"
 	"testing"
 )
 
 func Test_Encode(t *testing.T) {
 	// SetLogger(log.New(os.Stdout, "POCSAG ", log.LstdFlags))
-	enc, left := Generate(3000, 576, []*Message{
+	enc, left := Generate([]*Message{
 		&Message{1300100, "happy christmas!"},
 	})
 	if len(left) != 0 {
 		t.Errorf("expect no message left, got %v", left)
 	}
 
-	expect := []uint32{
+	expect := Burst{
 		// 18 words, 576 bits of preamble
 		0xAAAAAAAA, 0xAAAAAAAA,
 		0xAAAAAAAA, 0xAAAAAAAA, 0xAAAAAAAA, 0xAAAAAAAA, 0xAAAAAAAA, 0xAAAAAAAA, 0xAAAAAAAA, 0xAAAAAAAA,
@@ -27,7 +25,7 @@ func Test_Encode(t *testing.T) {
 	}
 
 	if len(enc) != len(expect) {
-		t.Errorf("expected:\n%X\ngot:\n%X\n", expect, enc)
+		t.Errorf("expected:\n%s\ngot:\n%s\n", expect, enc)
 	} else {
 		for i, w := range expect {
 			if w != enc[i] {
@@ -35,4 +33,6 @@ func Test_Encode(t *testing.T) {
 			}
 		}
 	}
+	t.Log(enc)
+	t.Log(enc.Bytes())
 }