improve pocsag alpha decoding

Author: AlexandreRouma

CMakeLists.txt

@@ -43,7 +43,7 @@ option(OPT_BUILD_FALCON9_DECODER "Build the falcon9 live decoder (Dependencies:
 option(OPT_BUILD_KG_SSTV_DECODER "Build the KG SSTV (KG-STV) decoder module (no dependencies required)" OFF)
 option(OPT_BUILD_M17_DECODER "Build the M17 decoder module (Dependencies: codec2)" OFF)
 option(OPT_BUILD_METEOR_DEMODULATOR "Build the meteor demodulator module (no dependencies required)" ON)
-option(OPT_BUILD_PAGER_DECODER "Build the pager decoder module (no dependencies required)" OFF)
+option(OPT_BUILD_PAGER_DECODER "Build the pager decoder module (no dependencies required)" ON)
 option(OPT_BUILD_RADIO "Main audio modulation decoder (AM, FM, SSB, etc...)" ON)
 option(OPT_BUILD_WEATHER_SAT_DECODER "Build the HRPT decoder module (no dependencies required)" OFF)
 

decoder_modules/pager_decoder/src/pocsag/pocsag.cpp

@@ -84,27 +84,13 @@ namespace pocsag {
 
     void Decoder::flushMessage() {
         if (!msg.empty()) {
-
-            // Unpack bits
-            std::string outStr = "";
-            for (int i = 0; (i+7) <= msg.size(); i += 7) {
-                uint8_t b0 = msg[i];
-                uint8_t b1 = msg[i+1];
-                uint8_t b2 = msg[i+2];
-                uint8_t b3 = msg[i+3];
-                uint8_t b4 = msg[i+4];
-                uint8_t b5 = msg[i+5];
-                uint8_t b6 = msg[i+6];
-                outStr += (char)((b6<<6) | (b5<<5) | (b4<<4) | (b3<<3) | (b2<<2) | (b1<<1) | b0);
-            }
-            onMessage(addr, msgType, outStr);
-
-            // // Send out message
-            // onMessage(addr, msgType, msg);
+            // Send out message
+            onMessage(addr, msgType, msg);
 
             // Reset state
             msg.clear();
-            leftInLast = 0;
+            currChar = 0;
+            currOffset = 0;
         }
     }
 
@@ -160,42 +146,27 @@ namespace pocsag {
                 // Decode data depending on message type
                 if (msgType == MESSAGE_TYPE_NUMERIC) {
                     // Numeric messages pack 5 characters per message codeword
-                    //msg += NUMERIC_CHARSET[(data >> 16) & 0b1111];
-                    //msg += NUMERIC_CHARSET[(data >> 12) & 0b1111];
-                    //msg += NUMERIC_CHARSET[(data >> 8) & 0b1111];
-                    //msg += NUMERIC_CHARSET[(data >> 4) & 0b1111];
-                    //msg += NUMERIC_CHARSET[data & 0b1111];
+                    msg += NUMERIC_CHARSET[(data >> 16) & 0b1111];
+                    msg += NUMERIC_CHARSET[(data >> 12) & 0b1111];
+                    msg += NUMERIC_CHARSET[(data >> 8) & 0b1111];
+                    msg += NUMERIC_CHARSET[(data >> 4) & 0b1111];
+                    msg += NUMERIC_CHARSET[data & 0b1111];
                 }
                 else if (msgType == MESSAGE_TYPE_ALPHANUMERIC) {
-                    // // Alpha messages pack 7bit characters in the entire codeword stream
-                    // int lasti;
-                    // for (int i = -leftInLast; i <= POCSAG_DATA_BITS_PER_CW-7; i += 7) {
-                    //     // Read 7 bits
-                    //     char c = 0;
-                    //     if (i < 0) {
-                    //         c = (lastMsgData & ((1 << (-i)) - 1)) << (7+i);
-                    //     }
-                    //     c |= (data >> (13 - i)) & 0b1111111;
-
-                    //     // Save character
-                    //     bitswapChar(c, c);
-                    //     msg += c;
-
-                    //     // Update last successful unpack
-                    //     lasti = i;
-                    // }
-
-                    // // Save how much is still left to read
-                    // leftInLast = 20 - (lasti + 7);
-
-                    // Pack the bits backwards
+                    // Unpack ascii bits 7 at a time (TODO: could be more efficient)
                     for (int i = 19; i >= 0; i--) {
-                        msg += (char)((data >> i) & 1);
+                        // Append bit to char
+                        currChar |= ((data >> i) & 1) << (currOffset++);
+
+                        // When the char is full, append to message
+                        if (currOffset >= 7) {
+                            // TODO: maybe replace with std::isprint
+                            if (currChar) { msg += currChar; }
+                            currChar = 0;
+                            currOffset = 0;
+                        }
                     }
                 }
-
-                // Save last data
-                lastMsgData = data;
             }
         }
     }

decoder_modules/pager_decoder/src/pocsag/pocsag.h

@@ -45,7 +45,7 @@ namespace pocsag {
         MessageType msgType;
         std::string msg;
 
-        uint32_t lastMsgData;
-        bool leftInLast = 0;
+        char currChar = 0;
+        int currOffset = 0;
     };
 }