Remove IQ buffer from decoder, implement buffer for sample dumping in…

… main program.

decode/decode.go

@@ -97,7 +97,6 @@ type Decoder struct {
 	Decimation int
 	DecCfg     PacketConfig
 
-	IQ        []byte
 	Signal    []float64
 	Filtered  []float64
 	Quantized []byte
@@ -132,7 +131,6 @@ func NewDecoder(cfg PacketConfig, decimation int) (d Decoder) {
 	d.DecCfg = d.Cfg.Decimate(d.Decimation)
 
 	// Allocate necessary buffers.
-	d.IQ = make([]byte, d.Cfg.BufferLength<<1)
 	d.Signal = make([]float64, d.DecCfg.BlockSize+d.DecCfg.SymbolLength2)
 	d.Filtered = make([]float64, d.DecCfg.BlockSize)
 	d.Quantized = make([]byte, d.DecCfg.BufferLength)
@@ -171,13 +169,11 @@ func NewDecoder(cfg PacketConfig, decimation int) (d Decoder) {
 // Decode accepts a sample block and performs various DSP techniques to extract a packet.
 func (d Decoder) Decode(input []byte) []int {
 	// Shift buffers to append new block.
-	copy(d.IQ, d.IQ[d.Cfg.BlockSize<<1:])
 	copy(d.Signal, d.Signal[d.DecCfg.BlockSize:])
 	copy(d.Quantized, d.Quantized[d.DecCfg.BlockSize:])
-	copy(d.IQ[d.Cfg.PacketLength<<1:], input[:])
 
 	// Compute the magnitude of the new block.
-	d.demod.Execute(d.IQ[d.Cfg.PacketLength<<1:], d.Signal[d.DecCfg.SymbolLength2:])
+	d.demod.Execute(input, d.Signal[d.DecCfg.SymbolLength2:])
 
 	// Perform matched filter on new block.
 	d.Filter(d.Signal, d.Filtered)

main.go

@@ -17,10 +17,12 @@
 package main
 
 import (
+	"bytes"
 	"encoding/xml"
 	"flag"
 	"fmt"
 	"io"
+	"io/ioutil"
 	"log"
 	"os"
 	"os/signal"
@@ -121,6 +123,7 @@ func (rcvr *Receiver) Run() {
 	}()
 
 	block := make([]byte, rcvr.p.Cfg().BlockSize2)
+	sampleBuf := new(bytes.Buffer)
 
 	start := time.Now()
 	for {
@@ -138,6 +141,15 @@ func (rcvr *Receiver) Run() {
 				log.Fatal("Error reading samples: ", err)
 			}
 
+			// If dumping samples, discard the oldest block from the buffer if
+			// it's full and write the new block to it.
+			if *sampleFilename != os.DevNull {
+				if sampleBuf.Len() > rcvr.p.Cfg().BufferLength<<1 {
+					io.CopyN(ioutil.Discard, sampleBuf, int64(len(block)))
+				}
+				sampleBuf.Write(block)
+			}
+
 			pktFound := false
 			indices := rcvr.p.Dec().Decode(block)
 
@@ -149,7 +161,7 @@ func (rcvr *Receiver) Run() {
 				var msg parse.LogMessage
 				msg.Time = time.Now()
 				msg.Offset, _ = sampleFile.Seek(0, os.SEEK_CUR)
-				msg.Length = rcvr.p.Cfg().BufferLength << 1
+				msg.Length = sampleBuf.Len()
 				msg.Message = pkt
 
 				err = encoder.Encode(msg)
@@ -175,7 +187,7 @@ func (rcvr *Receiver) Run() {
 
 			if pktFound {
 				if *sampleFilename != os.DevNull {
-					_, err = sampleFile.Write(rcvr.p.Dec().IQ)
+					_, err = sampleFile.Write(sampleBuf.Bytes())
 					if err != nil {
 						log.Fatal("Error writing raw samples to file:", err)
 					}