non blocking reads through channel and goroutine

ecu-2j.go

@@ -286,6 +286,8 @@ func readFirstBytesFromPortTwoj(fn string) ([]byte, error) {
 	fmt.Println("Serial cable set to:")
 	fmt.Println(mode)
 
+	go serialReadRoutine(sp)
+
 	sp.SetBreak(false)
 	time.Sleep(200 * time.Millisecond)
 
@@ -305,22 +307,10 @@ func readFirstBytesFromPortTwoj(fn string) ([]byte, error) {
 	readLoops := 0
 	readLoopsLimit := 200
 	for readLoops < readLoopsLimit {
-		readLoops++
-
-		// only read again if we don't have a full packet ready
-		// the reads are always blocking on linux even though they aren't in windows...
-		// TODO: move the serial reads and writes to their own go routines then it doesn't matter if it blocks
-		if len(buffer) <= 0 || len(buffer) < int(buffer[0])+2 {
-			rb := make([]byte, 256)
-			n, _ := sp.Read(rb[:])
-			rb = rb[0:n] // chop down to actual data size
-			buffer = append(buffer, rb...)
-
-			if n > 0 {
-				readLoops = 0 // reset timeout
-				// fmt.Print(hex.Dump(buffer))
-			}
-		}
+		// this timeout needs changing to time without an answer rather than number of loops
+		// readLoops++
+
+		buffer = append(buffer, nonBlockingSerialRead()...)
 
 		// clear leading zeros (from our wake up)
 		for len(buffer) > 0 && buffer[0] == 0x00 {
@@ -329,7 +319,8 @@ func readFirstBytesFromPortTwoj(fn string) ([]byte, error) {
 		}
 
 		if len(buffer) == 0 {
-			fmt.Println("buffer empty")
+			// fmt.Println("buffer empty")
+			time.Sleep(1 * time.Millisecond)
 			continue
 		}
 
@@ -347,7 +338,8 @@ func readFirstBytesFromPortTwoj(fn string) ([]byte, error) {
 		// TODO: check for implausible packet size
 
 		if len(buffer) < packetSize + 2 {
-			fmt.Println("waiting for rest of data packet")
+			// fmt.Println("waiting for rest of data packet")
+			time.Sleep(1 * time.Millisecond)
 			continue
 		}
 

main.go

@@ -27,6 +27,9 @@ var (
 	globalLogLines = []string{}
 
 	outgoingData chan string // for pushing data out of the websocket
+
+	serialReadChannel = make(chan byte, 1024)
+	// serialWriteChannel = make(chan byte, 1024)
 )
 
 func main() {

serialReadWrite.go

@@ -0,0 +1,33 @@
+package main
+
+import (
+	"github.com/distributed/sers"
+)
+// go routines for serial read
+// mostly because reads erroneously block in Linux, even with a timeout set
+
+func serialReadRoutine(sp sers.SerialPort) {
+    for {
+    	rb := make([]byte, 256)
+		n, _ := sp.Read(rb[:])
+		rb = rb[0:n] // chop down to actual data size
+		for i := 0; i < n; i++ {
+        	serialReadChannel <- rb[i]
+        }
+    }
+}
+
+// reads all currently available data from the channel
+func nonBlockingSerialRead() ([]byte) {
+	buffer := make([]byte, 0)
+	outer:
+	for {
+		select {
+		    case msg := <-serialReadChannel:
+		        buffer = append(buffer, msg)
+		    default:
+		        break outer
+	    }
+	}
+	return buffer
+}