Substantially refactor ~everything to separate concerns and improve flow clarity

Highlights:
- Remove all use of malloc and friends
- Refactor message handling functions to work with references
- Move core message read => triage => respond logic loop to main
  function
- Improve message triage and support follow-up messages
- Refactor hex byte parsing
- Disable periodic interrupt when not playing

.devcontainer/devcontainer.json

@@ -3,7 +3,7 @@
 {
 	"name": "AVR toolchain",
 	// Or use a Dockerfile or Docker Compose file. More info: https://containers.dev/guide/dockerfile
-	"image": "mcr.microsoft.com/devcontainers/base:alpine-3.18",
+	"image": "mcr.microsoft.com/devcontainers/base:alpine-3.22",
 	// Features to add to the dev container. More info: https://containers.dev/features.
 	"features": {},
 	// Use 'forwardPorts' to make a list of ports inside the container available locally.
@@ -14,12 +14,9 @@
 	"customizations": {
 		"vscode": {
 			"extensions": [
-				"ms-vscode.cpptools",
-				"ms-vscode.cmake-tools",
-				"rockcat.avr-support",
-				"harikrishnan94.cxx-compiler-explorer",
 				"ms-vscode.cpptools-extension-pack",
-				"twxs.cmake"
+				"rockcat.avr-support",
+				"harikrishnan94.cxx-compiler-explorer"
 			],
 			"settings": {
 				"editor.formatOnSave": true,

CMakeLists.txt

@@ -107,6 +107,7 @@ set(AVR_UPLOADTOOL_BASE_OPTIONS ${AVR_UPLOADTOOL_BASE_OPTIONS} -U syscfg1:w:0x4:
 add_avr_executable(mockingboard
     src/sniffer.c
     src/com232.c
+    src/queue.c
     src/avclandrv.c)
 
 target_link_options(mockingboard PUBLIC

src/avclandrv.c

@@ -96,7 +96,6 @@
 #include <stdlib.h>
 #include <string.h>
 
-#define VAR_DECLS
 #include "avclandrv.h"
 #include "com232.h"
 
@@ -130,8 +129,6 @@ uint8_t *cd_Track;
 uint8_t *cd_Time_Min;
 uint8_t *cd_Time_Sec;
 
-uint8_t answerReq;
-
 cd_modes CD_Mode;
 
 #ifdef SOFTWARE_DEBUG
@@ -148,17 +145,21 @@ const uint8_t list_functions_resp[] = {0x00, dev_COMM_CTRL, dev_COMM_v1,
 uint8_t ping_resp[] = {0x00, dev_COMM_CTRL, dev_COMM_v1, Ping_Resp, 0xFF, 0x00};
 uint8_t function_change_resp[] = {0x00, dev_CD_CHANGER, dev_COMM_v1, 0xFF,
                                   0x01};
-uint8_t cdstatus_resp[] = {dev_CD_CHANGER,
+
-                           dev_STATUS,
+#define STATUS_REPORT_DATA                                                     \
-                           Status_Report,
+  {dev_CD_CHANGER,                                                             \
-                           0x01,
+   dev_STATUS,                                                                 \
-                           cd_SEEKING_TRACK,
+   Status_Report,                                                              \
-                           0x01,
+   0x01,                                                                       \
-                           0x00,
+   cd_SEEKING_TRACK,                                                           \
-                           0xFF,
+   0x01,                                                                       \
-                           0x7F,
+   0x00,                                                                       \
-                           0x00,
+   0xFF,                                                                       \
-                           0x80};
+   0x7F,                                                                       \
+   0x00,                                                                       \
+   0x80}
+
+uint8_t cdstatus_resp[] = STATUS_REPORT_DATA;
 
 uint8_t cdinitreport_resp[] = {
     dev_CD_CHANGER, dev_STATUS, Initial_Report_Response, 0x01, 0x31, 0x10,
@@ -173,21 +174,19 @@ uint8_t cdloading_resp[] = {dev_CD_CHANGER,
                             0x01,
                             0x00,
                             0x01,
-                            0x00};
+                            0x02};
-
-uint8_t AVCLAN_handleframe(const AVCLAN_frame_t *frame);
-void AVCLAN_updateCDStatus();
 
 /* Disable serial and periodic interrupts during AVCLAN reads.
   Not using cli() because AVCLAN reads depend on other interrupts. */
 static inline void stopEvent() {
-  RTC.PITINTCTRL = 0x00; // PITINTCTRL allows resetting with full zero write.
+  cbi(RTC.PITINTCTRL, RTC_PI_bp);
   cbi(USART0.CTRLA, USART_RXCIE_bp);
 }
 
 // Re-enable serial and periodic interrupts.
 static inline void startEvent() {
-  sbi(RTC.PITINTCTRL, RTC_PI_bp); // Reenable PIT interrupt
+  if (AVCLAN_isPlaying()) // Reenable PIT interrupt if currently playing
+    sbi(RTC.PITINTCTRL, RTC_PI_bp);
   sbi(USART0.CTRLA, USART_RXCIE_bp);
 }
 
@@ -208,6 +207,50 @@ static inline void AVCLAN_setBusDriven() {
 }
 // clang-format on
 
+// Returns true if device TX is muted on AVCLAN bus
+static inline uint8_t AVCLAN_ismuted() {
+  return (((VPORTA_DIR & PIN4_bm) | (VPORTA_DIR & PIN0_bm)) == 0);
+}
+
+// Mute device TX on AVCLAN bus
+void AVCLAN_muteDevice(uint8_t mute) {
+  if (mute) {
+    // clang-format off
+    __asm__ __volatile__("cbi %[vporta_dir], 4; \n\t" // set as INPUT (output values ignored)
+                         "cbi %[vportc_dir], 0; \n\t" // set as INPUT (output values ignored)
+                         ::
+                         [vporta_dir] "I"(_SFR_IO_ADDR(VPORTA_DIR)),
+                         [vportc_dir] "I"(_SFR_IO_ADDR(VPORTC_DIR)));
+    // clang-format on
+  } else {
+    // clang-format off
+    __asm__ __volatile__("sbi %[vporta_dir], 4; \n\t"
+                         "sbi %[vportc_dir], 0; \n\t"
+                         ::
+                         [vporta_dir] "I"(_SFR_IO_ADDR(VPORTA_DIR)),
+                         [vportc_dir] "I"(_SFR_IO_ADDR(VPORTC_DIR)));
+    // clang-format on
+  }
+}
+
+// Sets CD_mode to play and resets timer count (so that the next interrupt is in
+// 1 sec)
+void AVCLAN_startPlaying() {
+  CD_Mode = stPlay;
+  cli();
+  loop_until_bit_is_clear(RTC_PITSTATUS, RTC_CNTBUSY_bp);
+  RTC.CNT = 0;
+  sbi(RTC.PITINTCTRL, RTC_PI_bp);
+  sei();
+}
+
+// Sets CD_mode to play and resets timer count (so that the next interrupt is in
+// 1 sec)
+void AVCLAN_stopPlaying() {
+  CD_Mode = stStop;
+  cbi(RTC.PITINTCTRL, RTC_PI_bp);
+}
+
 void AVCLAN_init() {
   // Pull-ups are disabled by default
   // Set pin 6 and 7 as input
@@ -248,8 +291,6 @@ void AVCLAN_init() {
 
   AVCLAN_muteDevice(0); // unmute AVCLAN bus TX
 
-  answerReq = cm_Null;
-
   cd_status.cd1 = 1;
   cd_status.disc = 1;
   cd_status.cd2 = cd_status.cd3 = cd_status.cd4 = cd_status.cd5 =
@@ -282,9 +323,9 @@ void incBCD(uint8_t *data) {
     *data += 1;
 }
 
-// Periodic interrupt with a 1 sec period
+uint8_t AVCLAN_isPlaying() { return (CD_Mode == stPlay); }
-ISR(RTC_PIT_vect) {
+
-  if (CD_Mode == stPlay) {
+void AVCLAN_incrementTime() {
   if (*cd_Time_Sec == 0x59) {
     *cd_Time_Sec = 0;
     if (*cd_Time_Min == 0x99) {
@@ -293,35 +334,11 @@ ISR(RTC_PIT_vect) {
       incBCD(cd_Time_Min);
   } else
     incBCD(cd_Time_Sec);
-    answerReq = cm_CDStatus;
-  }
-  RTC.PITINTFLAGS |= RTC_PI_bm;
 }
 
-// Mute device TX on AVCLAN bus
+void AVCLAN_setTime(uint8_t mins, uint8_t secs) {
-void AVCLAN_muteDevice(uint8_t mute) {
+  *cd_Time_Min = mins;
-  if (mute) {
+  *cd_Time_Sec = secs;
-    // clang-format off
-    __asm__ __volatile__("cbi %[vporta_dir], 4; \n\t"
-                         "cbi %[vportc_dir], 0; \n\t"
-                         ::
-                         [vporta_dir] "I"(_SFR_IO_ADDR(VPORTA_DIR)),
-                         [vportc_dir] "I"(_SFR_IO_ADDR(VPORTC_DIR)));
-    // clang-format on
-  } else {
-    // clang-format off
-    __asm__ __volatile__("sbi %[vporta_dir], 4; \n\t"
-                         "sbi %[vportc_dir], 0; \n\t"
-                         ::
-                         [vporta_dir] "I"(_SFR_IO_ADDR(VPORTA_DIR)),
-                         [vportc_dir] "I"(_SFR_IO_ADDR(VPORTC_DIR)));
-    // clang-format on
-  }
-}
-
-// Returns true if device TX is muted on AVCLAN bus
-static inline uint8_t AVCLAN_ismuted() {
-  return (((VPORTA_DIR & PIN4_bm) | (VPORTA_DIR & PIN0_bm)) == 0);
 }
 
 // Set AVC bus to `val` (logical 1 or 0) for `period` ticks of TCB1
@@ -539,7 +556,7 @@ uint8_t AVCLAN_readbyte(uint8_t *byte) {
   return (parity & 1);
 }
 
-uint8_t AVCLAN_readframe() {
+uint8_t AVCLAN_readframe(AVCLAN_frame_t *frame) {
   struct errtype {
     enum : uint8_t {
       STARTBIT_TIMEOUT = 0x01,
@@ -562,16 +579,6 @@ uint8_t AVCLAN_readframe() {
 
   stopEvent(); // disable timer1 interrupt
 
-  uint8_t data[MAXMSGLEN] = {0};
-  AVCLAN_frame_t frame = {
-      .broadcast = BROADCAST,
-      .controller_addr = 0x000,
-      .peripheral_addr = 0x000,
-      .control = 0xF,
-      .length = 0,
-      .data = data,
-  };
-
   uint8_t parity = 0;
   uint8_t tmp = 0;
 
@@ -589,44 +596,44 @@ uint8_t AVCLAN_readframe() {
   }
   // Otherwise that was a start bit
 
-  AVCLAN_readbits((uint8_t *)&frame.broadcast, 1);
+  AVCLAN_readbits(&frame->broadcast, 1);
 
-  parity = AVCLAN_readbits(&frame.controller_addr, 12);
+  parity = AVCLAN_readbits(&frame->controller_addr, 12);
   AVCLAN_readbits(&tmp, 1);
   if (parity != (tmp & 1)) {
     err.errno = BAD_CONTROLLER_PARITY;
     if (verbose) {
-      err.read_val = frame.controller_addr;
+      err.read_val = frame->controller_addr;
       err.parity = tmp & 1;
     }
     goto handle_err;
   }
 
-  parity = AVCLAN_readbits(&frame.peripheral_addr, 12);
+  parity = AVCLAN_readbits(&frame->peripheral_addr, 12);
   AVCLAN_readbits(&tmp, 1);
   if (parity != (tmp & 1)) {
     err.errno = BAD_PERIPHERAL_PARITY;
     if (verbose) {
-      err.read_val = frame.peripheral_addr;
+      err.read_val = frame->peripheral_addr;
       err.parity = tmp & 1;
     }
     goto handle_err;
   }
 
   uint8_t shouldACK =
-      !AVCLAN_ismuted() && (frame.peripheral_addr == DEVICE_ADDR);
+      !AVCLAN_ismuted() && (frame->peripheral_addr == DEVICE_ADDR);
 
   if (shouldACK)
     AVCLAN_sendbit_ACK();
   else
     AVCLAN_readbits(&tmp, 1);
 
-  parity = AVCLAN_readbits(&frame.control, 4);
+  parity = AVCLAN_readbits(&frame->control, 4);
   AVCLAN_readbits(&tmp, 1);
   if (parity != (tmp & 1)) {
     err.errno = BAD_CONTROL_PARITY;
     if (verbose) {
-      err.read_val = frame.control;
+      err.read_val = frame->control;
       err.parity = tmp & 1;
     }
     goto handle_err;
@@ -636,12 +643,12 @@ uint8_t AVCLAN_readframe() {
     AVCLAN_readbits(&tmp, 1);
   }
 
-  parity = AVCLAN_readbyte(&frame.length);
+  parity = AVCLAN_readbyte(&frame->length);
   AVCLAN_readbits(&tmp, 1);
   if (parity != (tmp & 1)) {
     err.errno = BAD_LENGTH_PARITY;
     if (verbose) {
-      err.read_val = frame.length;
+      err.read_val = frame->length;
       err.parity = tmp & 1;
     }
     goto handle_err;
@@ -651,19 +658,19 @@ uint8_t AVCLAN_readframe() {
     AVCLAN_readbits(&tmp, 1);
   }
 
-  if (frame.length == 0 || frame.length > MAXMSGLEN) {
+  if (frame->length == 0 || frame->length > MAXMSGLEN) {
     err.errno = BAD_LENGTH_RANGE;
-    err.val = frame.length;
+    err.val = frame->length;
     goto handle_err;
   }
 
-  for (uint8_t i = 0; i < frame.length; i++) {
+  for (uint8_t i = 0; i < frame->length; i++) {
-    parity = AVCLAN_readbyte(&frame.data[i]);
+    parity = AVCLAN_readbyte(&frame->data[i]);
     AVCLAN_readbits(&tmp, 1);
     if (parity != (tmp & 1)) {
       err.errno = BAD_DATA_PARITY;
       if (verbose) {
-        err.read_val = frame.data[i];
+        err.read_val = frame->data[i];
         err.parity = tmp & 1;
       }
       goto handle_err;
@@ -704,7 +711,6 @@ uint8_t AVCLAN_readframe() {
           RS232_PrintHex4(err.parity);
         }
     }
-
     RS232_Print("\n");
   } else {
     startEvent();
@@ -713,12 +719,7 @@ uint8_t AVCLAN_readframe() {
   if (printAllFrames &&
       (!err.errno ||
        err.errno > STARTBIT_LENGTH)) // At least partially successful read
-    AVCLAN_printframe(&frame, printBinary);
+    AVCLAN_printframe(frame, printBinary);
-
-  if (!!err.errno && !AVCLAN_ismuted()) // Only handle if successful
-    AVCLAN_handleframe(&frame);
-
-  answerReq = cm_Null;
 
   return err.errno;
 }
@@ -736,8 +737,10 @@ uint8_t AVCLAN_sendframe(const AVCLAN_frame_t *frame) {
     uint8_t val;
   } err = {0};
 
-  if ((err.errno = AVCLAN_ismuted()))
+  if (AVCLAN_ismuted()) {
+    err.errno = MUTED;
     goto handle_err;
+  }
 
   stopEvent();
 
@@ -854,53 +857,20 @@ uint8_t AVCLAN_sendframe(const AVCLAN_frame_t *frame) {
   return err.errno;
 }
 
-const AVCLAN_frame_t *frameQueue[4];
+response_t AVCLAN_handleframe(const AVCLAN_frame_t *in, AVCLAN_frame_t *resp) {
+  response_t respond = r_Nothing;
 
-static inline uint8_t qFull() {
+  if (AVCLAN_ismuted())
-  return ((qWrite - qRead) == sizeof(frameQueue));
+    return respond;
-}
-
-static inline uint8_t qMask(uint8_t pos) {
-  return pos & (sizeof(frameQueue) - 1);
-}
-
-uint8_t qPush(const AVCLAN_frame_t *frame) {
-  if (qFull())
-    return 1;
-
-  frameQueue[qMask(qWrite++)] = frame;
-
-  return 0;
-}
-
-const AVCLAN_frame_t *qPeek() {
-  if (qEmpty())
-    return NULL;
-
-  return frameQueue[qMask(qRead)];
-}
-
-const AVCLAN_frame_t *qPop() {
-  if (qEmpty())
-    return NULL;
-
-  return frameQueue[qMask(qRead++)];
-}
-
-uint8_t AVCLAN_handleframe(const AVCLAN_frame_t *frame) {
-  uint8_t respond = 0;
-  AVCLAN_frame_t *resp = malloc(sizeof(AVCLAN_frame_t));
-  if (!resp)
-    return NULL;
 
   resp->controller_addr = DEVICE_ADDR;
   resp->control = 0xF;
 
-  uint8_t *data = frame->data;
+  uint8_t *data = in->data;
   uint8_t from;
 
   // BROADCAST
-  if (frame->broadcast == 0) {
+  if (in->broadcast == 0) {
     // skip confirming peripheral_addr, because it  will be 0xFFF or 0x1FF based
     // on all currently known examples
     switch (*data++ /* data[0] == "from" device */) {
@@ -927,8 +897,8 @@ uint8_t AVCLAN_handleframe(const AVCLAN_frame_t *frame) {
               LAN_RESPONSE:
                 resp->broadcast = UNICAST;
                 resp->peripheral_addr = HU_ADDR;
-                resp->data = (uint8_t *)lancheck_resp;
+                memcpy(resp->data, lancheck_resp, sizeof(lancheck_resp));
-                respond = 1;
+                respond = r_Handled;
             }
             break;
           default:
@@ -939,23 +909,30 @@ uint8_t AVCLAN_handleframe(const AVCLAN_frame_t *frame) {
         if (*data++ /* data[1] == "to" device */ == dev_COMM_CTRL) {
           switch (*data++ /* data[2] == device action */) {
             case Current_Function:
-              CD_Mode =
+              if ((*data++ /* data[2] */ == dev_CD_CHANGER) &&
-                  (*data++ /* data[2] */ == dev_CD_CHANGER) ? stPlay : stStop;
+                  !AVCLAN_isPlaying()) {
+                cd_status.state = cd_SEEKING | cd_SEEKING_TRACK;
+                cd_status.flags2 = 0x80;
+                AVCLAN_startPlaying();
+                AVCLAN_generateStatus(resp);
+                respond = r_NormalizeState;
+              }
               break;
             case Ping_Req:
               resp->broadcast = UNICAST;
               resp->peripheral_addr = HU_ADDR;
               resp->length = sizeof(ping_resp);
               ping_resp[4] = *data++ /* data[2] */;
-              resp->data = (uint8_t *)&ping_resp;
+              memcpy(resp->data, ping_resp, sizeof(ping_resp));
-              respond = 1;
+              respond = r_Handled;
               break;
             case List_Functions_Req:
               resp->broadcast = UNICAST;
               resp->peripheral_addr = HU_ADDR;
               resp->length = sizeof(list_functions_resp);
-              resp->data = (uint8_t *)&list_functions_resp;
+              memcpy(resp->data, list_functions_resp,
-              respond = 1;
+                     sizeof(list_functions_resp));
+              respond = r_Handled;
               break;
             // case Restart_Lan:
             //   break;
@@ -965,7 +942,7 @@ uint8_t AVCLAN_handleframe(const AVCLAN_frame_t *frame) {
         break;
       default:
     }
-  } else if (frame->peripheral_addr == DEVICE_ADDR) { // unicast to CD changer
+  } else if (in->peripheral_addr == DEVICE_ADDR) { // unicast to CD changer
     if (*data++ == 0) { // unicasts begin with a zero-byte
       from = *data++;   /* data[1] */
       switch (from) {
@@ -976,22 +953,21 @@ uint8_t AVCLAN_handleframe(const AVCLAN_frame_t *frame) {
               switch (*data++ /* data[3] == device action */) {
                 case Enable_Function_Req:
                   function_change_resp[3] = Enable_Function_Resp;
-                  cd_status.state = cd_SEEKING | cd_PLAYBACK | cd_SEEKING_TRACK;
+                  cd_status.state = cd_SEEKING | cd_SEEKING_TRACK;
-                  cd_status.flags2 = 0x80;
+                  cd_status.flags2 = 0xc0;
-                  *cd_Time_Min = 0xff;
+                  // *cd_Time_Min = 0xff;
-                  *cd_Time_Sec = 0x7f;
+                  // *cd_Time_Sec = 0x7f;
-                  CD_Mode = stPlay;
+                  AVCLAN_startPlaying();
-                  // trigger regular status update after
+                  respond = r_StartPlaying;
-                  answerReq = cm_CDStatus;
                   goto FUNCTION_CHANGE_RESPONSE;
                 case Disable_Function_Req:
+                  AVCLAN_stopPlaying();
                   function_change_resp[3] = Disable_Function_Resp;
-                  CD_Mode = stStop;
+                  cd_status.state = cd_PLAYBACK | cd_SEEKING_TRACK;
-                  cd_status.state = 0;
+                  // *cd_Time_Min = 0x00;
-                  *cd_Time_Min = 0x00;
+                  // *cd_Time_Sec = 0x00;
-                  *cd_Time_Sec = 0x00;
+                  cd_status.flags2 = 0x80;
-                  // trigger regular status update after
+                  respond = r_StatusReport;
-                  answerReq = cm_CDStatus;
                   goto FUNCTION_CHANGE_RESPONSE;
                 default:
                   break;
@@ -999,8 +975,8 @@ uint8_t AVCLAN_handleframe(const AVCLAN_frame_t *frame) {
                   resp->broadcast = UNICAST;
                   resp->peripheral_addr = HU_ADDR;
                   resp->length = sizeof(function_change_resp);
-                  resp->data = (uint8_t *)&function_change_resp;
+                  memcpy(resp->data, function_change_resp,
-                  respond = 1;
+                         sizeof(function_change_resp));
               }
               break;
             default:
@@ -1012,41 +988,47 @@ uint8_t AVCLAN_handleframe(const AVCLAN_frame_t *frame) {
               switch (*data++ /* data[3] == device action */) {
                 case Initial_Report_Request:
                   resp->length = sizeof(cdinitreport_resp);
-                  resp->data = (uint8_t *)&cdinitreport_resp;
+                  memcpy(resp->data, cdinitreport_resp,
+                         sizeof(cdinitreport_resp));
+                  resp->data[1] = from; // respond to device that requested
                   goto CMD_SW_RESPONSE;
                 case Playback_Request:
-                  cdstatus_resp[1] = from; // respond to device that requested
+                  resp->data[1] = from; // respond to device that requested
-                  cdstatus_resp[2] = Playback_Report;
+                  resp->data[2] = Playback_Report;
                   resp->length = sizeof(cdstatus_resp);
-                  memcpy(&cdstatus_resp[3], &cd_status, sizeof(cd_status));
+                  memcpy(&resp->data[3], &cd_status, sizeof(cd_status));
-                  resp->data = (uint8_t *)&cdstatus_resp;
                   goto CMD_SW_RESPONSE;
                 case Loading_Request2:
-                  cdloading_resp[1] = from;
-                  cdloading_resp[2] = Loading_Response2;
                   resp->length = sizeof(cdloading_resp);
-                  resp->data = (uint8_t *)&cdloading_resp;
+                  memcpy(&resp->data, &cdloading_resp, sizeof(cdloading_resp));
+                  resp->data[1] = from;
+                  resp->data[2] = Loading_Response2;
                   goto CMD_SW_RESPONSE;
                 case Track_Seek_Up:
                   cd_status.state = cd_SEEKING_TRACK;
                   (*cd_Track)++;
                   *cd_Time_Min = 0xff;
                   *cd_Time_Sec = 0x7f;
+                  cd_status.scan = 1;
                   cd_status.flags2 = 0xc0;
-                  goto CMD_SW_RESPONSE;
+                  respond = r_TrackChange;
+                  AVCLAN_generateStatus(resp);
+                  break;
                 case Track_Seek_Down:
                   cd_status.state = cd_SEEKING_TRACK;
                   (*cd_Track)--;
                   *cd_Time_Min = 0xff;
                   *cd_Time_Sec = 0x7f;
+                  cd_status.scan = 1;
                   cd_status.flags2 = 0xc0;
-                  goto CMD_SW_RESPONSE;
+                  respond = r_TrackChange;
+                  AVCLAN_generateStatus(resp);
+                  break;
                 default:
                   break;
                 CMD_SW_RESPONSE:
                   resp->broadcast = UNICAST;
-                  resp->peripheral_addr = frame->controller_addr;
+                  resp->peripheral_addr = HU_ADDR;
-                  respond = 1;
               }
               break;
             default:
@@ -1058,27 +1040,27 @@ uint8_t AVCLAN_handleframe(const AVCLAN_frame_t *frame) {
               switch (*data++ /* data[3] == device action */) {
                 case Initial_Report_Request:
                   resp->length = sizeof(cdinitreport_resp);
-                  resp->data = (uint8_t *)&cdinitreport_resp;
+                  memcpy(resp->data, cdinitreport_resp,
+                         sizeof(cdinitreport_resp));
+                  resp->data[1] = from; // respond to device that requested
                   goto STATUS_RESPONSE;
                 case Playback_Request:
-                  cdstatus_resp[1] = from; // respond to device that requested
+                  resp->data[1] = from; // respond to device that requested
-                  cdstatus_resp[2] = Playback_Report;
+                  resp->data[2] = Playback_Report;
                   resp->length = sizeof(cdstatus_resp);
-                  memcpy(&cdstatus_resp[3], &cd_status, sizeof(cd_status));
+                  memcpy(&resp->data[3], &cd_status, sizeof(cd_status));
-                  resp->data = (uint8_t *)&cdstatus_resp;
                   goto STATUS_RESPONSE;
                 case Loading_Request2:
-                  cdloading_resp[1] = from;
-                  cdloading_resp[2] = Loading_Response2;
                   resp->length = sizeof(cdloading_resp);
-                  resp->data = (uint8_t *)&cdloading_resp;
+                  memcpy(&resp->data, &cdloading_resp, sizeof(cdloading_resp));
+                  resp->data[1] = from;
+                  resp->data[2] = Loading_Response2;
                   goto STATUS_RESPONSE;
                 default:
                   break;
                 STATUS_RESPONSE:
                   resp->broadcast = UNICAST;
-                  resp->peripheral_addr = frame->controller_addr;
+                  resp->peripheral_addr = HU_ADDR;
-                  respond = 1;
               }
               break;
             default:
@@ -1089,40 +1071,17 @@ uint8_t AVCLAN_handleframe(const AVCLAN_frame_t *frame) {
     }
   }
 
-  if (!respond) {
-    free(resp);
-  } else {
-    qPush(resp);
-  }
-
   return respond;
 }
 
-uint8_t AVCLAN_respond() {
+uint8_t AVCLAN_tryrespond(const AVCLAN_frame_t *resp) {
   uint8_t r = 0;
-  if (!qEmpty()) {
-    const AVCLAN_frame_t *resp = qPeek();
   for (uint8_t i = 0; i < MAX_SEND_ATTEMPTS; i++) {
     r = AVCLAN_sendframe(resp);
-      if (!r) { // Send succeeded
+    if (!r) // Send succeeded
-        resp = qPop();
-        free((AVCLAN_frame_t *)resp);
       break;
   }
-    }
-    if (r) { // Sending failed all attempts; give up sending frame
-      resp = qPop();
-      free((AVCLAN_frame_t *)resp);
-    }
-  } else {
-    switch (answerReq) {
-      case cm_Null: break;
-      case cm_CDStatus: AVCLAN_updateCDStatus(); break;
-      default:
-    }
-  }
 
-  answerReq = cm_Null;
   return r;
 }
 
@@ -1180,10 +1139,10 @@ uint8_t AVCLAN_parseframe(const uint8_t *bytes, uint8_t len,
   } err = {0};
 
   if (len < sizeof(AVCLAN_frame_t)) {
-    err.erno = TOO_SHORT;
+    err.errno = TOO_SHORT;
     goto handle_err;
   }
-  uint8_t *last = bytes + len;
+  const uint8_t *last = bytes + len;
 
   frame->broadcast = *bytes++;
   frame->controller_addr = *(uint16_t *)bytes++;
@@ -1218,30 +1177,42 @@ uint8_t AVCLAN_parseframe(const uint8_t *bytes, uint8_t len,
   return err.errno;
 }
 
-void AVCLAN_updateCDStatus() {
+// Only used for regularly scheduled periodic updates
-  if (CD_Mode) {
+AVCLAN_frame_t *AVCLAN_getStatusFrame() {
-    if (answerReq == cm_CDStatus) {
+  static uint8_t status_data[] = STATUS_REPORT_DATA;
-      cdstatus_resp[2] = Status_Report;
+  static AVCLAN_frame_t status = {.broadcast = BROADCAST,
-      memcpy(&cdstatus_resp[3], &cd_status, sizeof(cd_status));
+                                  .controller_addr = DEVICE_ADDR,
+                                  .peripheral_addr = 0x1FF,
+                                  .control = 0xF,
+                                  .length = sizeof(status_data),
+                                  .data = status_data};
 
-      AVCLAN_frame_t status = {.broadcast = BROADCAST,
+  return &status;
+}
+
+// Used for changed status messages
+void AVCLAN_generateStatus(AVCLAN_frame_t *status) {
+  *status = (AVCLAN_frame_t){
+      .broadcast = BROADCAST,
       .controller_addr = DEVICE_ADDR,
       .peripheral_addr = 0x1FF,
       .control = 0xF,
       .length = sizeof(cdstatus_resp),
-                               .data = (uint8_t *)&cdstatus_resp};
+      .data = status->data, // don't overwrite data pointer
-
+  };
-      AVCLAN_sendframe(&status);
+  status->data[0] = dev_CD_CHANGER;
+  status->data[1] = dev_STATUS;
+  status->data[2] = Status_Report;
+  memcpy(&status->data[3], &cd_status, sizeof(cd_status));
 }
 
-    if (cd_status.state != cd_PLAYBACK) {
+void AVCLAN_normalizeState() {
+  // if (cd_status.state != cd_PLAYBACK) {
   cd_status.state = cd_PLAYBACK;
+  cd_status.disk_scan = 0;
+  cd_status.scan = 0;
   cd_status.flags2 = 0x80;
-      *cd_Time_Min = 0x00;
+  // }
-      *cd_Time_Sec = 0x00;
-      answerReq = cm_CDStatus;
-    }
-  }
 }
 
 #ifdef SOFTWARE_DEBUG

src/avclandrv.h

@@ -75,6 +75,8 @@ typedef enum {
   Lancheck_Scan_Resp = 0x1a,
   Lancheck_Req = 0x0c,
   Lancheck_Resp = 0x1c,
+  // Lancheck_UNK_Req = 0x0d,
+  // Lancheck_UNK_Resp = 0x1d,
   Ping_Req = 0x20,
   Ping_Resp = 0x30,
 
@@ -169,6 +171,16 @@ typedef struct AVCLAN_CD_Status {
 
 typedef enum { stStop = 0, stPlay = 1 } cd_modes;
 
+typedef enum : uint8_t {
+  r_Nothing = 0x00,
+  r_Handled,             // No follow-up needed
+  r_StatusReport = 0x02, // Needs follow-up status report
+  r_NormalizeState,      // cd_status needs normalized and resent
+  r_StartPlaying,        // started playing; send current status and then
+                         // normalize
+  r_TrackChange,         // Time needs reset
+} response_t;
+
 typedef enum MSG_TYPE { BROADCAST = 0, UNICAST = 1 } MSG_TYPE_t;
 
 typedef struct AVCLAN_frame_struct {
@@ -180,33 +192,28 @@ typedef struct AVCLAN_frame_struct {
   uint8_t *data;
 } AVCLAN_frame_t;
 
+typedef struct RFrame_struct {
+  response_t r;
+  AVCLAN_frame_t *frame;
+} RFrame_t;
+
 void AVCLAN_init();
 void AVCLAN_muteDevice(uint8_t mute);
 
-uint8_t AVCLAN_readframe();
+uint8_t AVCLAN_readframe(AVCLAN_frame_t *frame);
+response_t AVCLAN_handleframe(const AVCLAN_frame_t *in, AVCLAN_frame_t *out);
 uint8_t AVCLAN_sendframe(const AVCLAN_frame_t *frame);
-
+uint8_t AVCLAN_tryrespond(const AVCLAN_frame_t *frame);
-// To allow inlining qEmpty and AVCLAN_responseNeeded
-#ifndef VAR_DECLS
-  #define _DECL extern
-  #define _INIT(x)
-#else
-  #define _DECL
-  #define _INIT(x) = x
-#endif
-_DECL uint8_t answerReq _INIT(0);
-_DECL uint8_t qWrite _INIT(0);
-_DECL uint8_t qRead _INIT(0);
-extern cd_modes CD_Mode;
-
-inline uint8_t qEmpty() { return (qWrite == qRead); }
-inline uint8_t AVCLAN_responseNeeded() { return (answerReq != 0) || !qEmpty(); }
-
-uint8_t AVCLAN_respond();
-
 void AVCLAN_printframe(const AVCLAN_frame_t *frame, uint8_t binary);
 uint8_t AVCLAN_parseframe(const uint8_t *bytes, uint8_t len,
                           AVCLAN_frame_t *frame);
+AVCLAN_frame_t *AVCLAN_getStatusFrame();
+void AVCLAN_generateStatus(AVCLAN_frame_t *status);
+
+uint8_t AVCLAN_isPlaying();
+void AVCLAN_incrementTime();
+void AVCLAN_setTime(uint8_t mins, uint8_t secs);
+void AVCLAN_normalizeState();
 
 #ifdef SOFTWARE_DEBUG
 void AVCLan_Measure();

src/queue.c

@@ -0,0 +1,58 @@
+#include <stddef.h>
+#include <stdint.h>
+
+#include "avclandrv.h"
+#include "queue.h"
+
+void constructQueue(Queue_t *q, void *buf, uint8_t size, uint8_t len,
+                    uint8_t constructFull) {
+  q->read = 0;
+  q->size = len;
+  if (!!constructFull) {
+    q->write = len;
+
+    for (uint8_t i = 0; i < len; ++i) {
+      q->buf[i] = buf;
+      buf = (char *)buf + size;
+    }
+  } else {
+    q->write = 0;
+  }
+}
+
+void constructEmptyQueue(Queue_t *q, uint8_t size, uint8_t len) {
+  constructQueue(q, NULL, size, len, 0);
+}
+
+uint8_t isEmpty(const Queue_t *q) { return (q->write == q->read); }
+
+static inline uint8_t isFull(const Queue_t *q) {
+  return ((q->write - q->read) == q->size);
+}
+
+static inline uint8_t qMask(const Queue_t *q, uint8_t pos) {
+  return pos & (q->size - 1);
+}
+
+uint8_t pushQueue(Queue_t *q, void *x) {
+  if (isFull(q))
+    return 1;
+
+  q->buf[qMask(q, q->write++)] = x;
+
+  return 0;
+}
+
+const void *peekQueue(const Queue_t *q) {
+  if (isEmpty(q))
+    return NULL;
+
+  return q->buf[qMask(q, q->read)];
+}
+
+void *popQueue(Queue_t *q) {
+  if (isEmpty(q))
+    return NULL;
+
+  return q->buf[qMask(q, q->read++)];
+}

src/queue.h

@@ -0,0 +1,18 @@
+#pragma once
+
+#include <stdint.h>
+
+typedef struct Queue_struct {
+  uint8_t write;
+  uint8_t read;
+  uint8_t size;
+  void *buf[];
+} Queue_t;
+
+void constructQueue(Queue_t *q, void *buf, uint8_t size, uint8_t len,
+                    uint8_t constructFull);
+void constructEmptyQueue(Queue_t *q, uint8_t size, uint8_t len);
+uint8_t isEmpty(const Queue_t *q);
+uint8_t pushQueue(Queue_t *q, void *x);
+const void *peekQueue(const Queue_t *q);
+void *popQueue(Queue_t *q);

src/sniffer.c

@@ -24,12 +24,15 @@
 #include <avr/io.h>
 #include <avr/sfr_defs.h>
 #include <avr/xmega.h>
+#include <ctype.h>
+#include <stddef.h>
 #include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
 
 #include "avclandrv.h"
 #include "com232.h"
+#include "queue.h"
 
 uint8_t echoCharacters;
 uint8_t readBinary;
@@ -38,23 +41,61 @@ uint8_t readkey;
 
 const char *const offon[] = {"OFF", "ON"};
 
+#define CACHE_SIZE 16
+
+AVCLAN_frame_t frames[CACHE_SIZE];
+RFrame_t responses[CACHE_SIZE];
+uint8_t framesdata[CACHE_SIZE][MAXMSGLEN];
+
+Queue_t cache, rcache, incoming, outgoing;
+
+volatile uint8_t enqueueStatus = 0;
+
 void Setup();
 void general_GPIO_init();
 void print_help();
 
+static uint8_t return_resp(RFrame_t *resp) {
+  uint8_t err;
+  AVCLAN_frame_t *out = resp->frame;
+  if ((out >= frames) && (out < &frames[CACHE_SIZE]))
+    // only return cache-owned frames (e.g. not status, etc)
+    err = pushQueue(&cache, out);
+  err = pushQueue(&rcache, resp);
+  return err;
+}
+
+static uint8_t push_or_return_resp(RFrame_t *resp) {
+  uint8_t err = pushQueue(&outgoing, resp) && return_resp(resp);
+  return err;
+}
+
 int main() {
   uint8_t readSeq = 0;
-  uint8_t s_len = 0;
+  uint8_t hexChars[2];
-  uint8_t s_dig = 0;
+  uint8_t hexDigit = 0; // current digit being written to hexChars
-  uint8_t s_c[2];
+
-  uint8_t i;
+  MSG_TYPE_t seqBroadcast = BROADCAST;
+  uint8_t lastPrintAllFrames = 1;
+
   uint8_t data_tmp[MAXMSGLEN];
-  AVCLAN_frame_t msg = {
+  uint8_t seqLen = 0; // current length written to data_tmp
-      .broadcast = UNICAST,
+
-      .controller_addr = DEVICE_ADDR,
+  uint8_t err = 0;
-      .control = 0xF,
+
-      .data = data_tmp,
+  AVCLAN_frame_t *msg, *out;
-  };
+  RFrame_t *resp;
+  AVCLAN_frame_t *status = AVCLAN_getStatusFrame();
+
+  for (uint8_t i = 0; i < CACHE_SIZE; ++i) {
+    frames[i].data = framesdata[i];
+    frames[i].control = 0x0f;
+  }
+
+  constructQueue(&cache, frames, sizeof(AVCLAN_frame_t), CACHE_SIZE, 1);
+  constructEmptyQueue(&incoming, sizeof(AVCLAN_frame_t), CACHE_SIZE);
+  constructQueue(&rcache, responses, sizeof(RFrame_t), CACHE_SIZE, 1);
+  constructEmptyQueue(&outgoing, sizeof(RFrame_t), CACHE_SIZE);
 
   Setup();
   print_help();
@@ -62,16 +103,89 @@ int main() {
   while (1) {
 
     if (!BUS_IS_IDLE) {
-      AVCLAN_readframe();
+      msg = (AVCLAN_frame_t *)(&cache);
-    } else if (AVCLAN_responseNeeded()) {
+      if (!msg) {
-      AVCLAN_respond();
+        RS232_Print("!! Dropping an incoming message; cache is empty !!");
+        continue;
+      }
+
+      err = AVCLAN_readframe(msg);
+      if (!err)
+        err = pushQueue(&incoming, msg) && pushQueue(&cache, msg);
+    } else if (!isEmpty(&incoming)) {
+      out = (AVCLAN_frame_t *)popQueue(&cache);
+      if (!out) {
+        RS232_Print("!! Unable to respond; cache is empty !!");
+        continue;
+      }
+
+      msg = (AVCLAN_frame_t *)popQueue(
+          &incoming); // prior !isempty(incoming) guarantees success
+      response_t respond = AVCLAN_handleframe(msg, out);
+
+      if (respond) {
+        resp = (RFrame_t *)popQueue(&rcache);
+        if (resp) {
+          *resp = (RFrame_t){.r = respond, .frame = out};
+          push_or_return_resp(resp);
+        } else
+          pushQueue(&cache, out);
+      } else // no response needed; return to circulation
+        pushQueue(&cache, out);
+
+      pushQueue(&cache, msg);
+    } else if (!isEmpty(&outgoing)) {
+      resp = (RFrame_t *)popQueue(
+          &outgoing); // prior !isempty(outgoing) guarantees success
+      out = resp->frame;
+      err = AVCLAN_sendframe(out);
+      if (err) {
+        RS232_Print("!! Failed to send frame; error code ");
+        RS232_PrintHex(err);
+        RS232_Print(" !!\n");
+        return_resp(resp);
+      } else {
+        // Re-use successful resp for sequence
+        switch (resp->r) {
+          case r_TrackChange: AVCLAN_setTime(0x00, 0x00); // fallthrough
+          case r_NormalizeState:
+            AVCLAN_normalizeState(out);
+            resp->r = r_Handled;
+            push_or_return_resp(resp);
+            break;
+          case r_StartPlaying:
+            AVCLAN_generateStatus(out);
+            resp->r = r_NormalizeState;
+            push_or_return_resp(resp);
+            break;
+          case r_StatusReport:
+            AVCLAN_generateStatus(out);
+            resp->r = r_Handled;
+            push_or_return_resp(resp);
+            break;
+          case r_Nothing: __builtin_unreachable();
+          case r_Handled: return_resp(resp); break;
+        }
+      }
+    } else if (enqueueStatus) {
+      AVCLAN_generateStatus(status);
+      resp = (RFrame_t *)popQueue(&rcache);
+      if (resp) {
+        *resp = (RFrame_t){.r = r_Handled, .frame = status};
+        err = pushQueue(&outgoing, resp);
+        if (err) {
+          RS232_Print("Outgoing queue full; unable to send status update");
+          pushQueue(&rcache, resp);
+        } else
+          enqueueStatus = 0; // Only clear if successful
+      }
+      // no further error handling needed; status isn't part of the cache
     }
 
     // Key handler
     if (RS232_RxCharEnd) {
       cli();
-      readkey = RS232_RxCharBuffer[RS232_RxCharBegin];
+      readkey = RS232_RxCharBuffer[RS232_RxCharBegin++];
-      RS232_RxCharBegin++;
       if (RS232_RxCharBegin == RS232_RxCharEnd)  // if buffer is consumed
         RS232_RxCharBegin = RS232_RxCharEnd = 0; // reset buffer
       sei();
@@ -84,6 +198,9 @@ int main() {
           RS232_Print("\n");
           break;
         case 'X':
+          // X/x isn't a single toggle interface because this is used
+          // programmatically and is simpler than reading the toggle
+          // state
           printBinary = 1;
           RS232_Print("Binary: ");
           RS232_Print(offon[1]);
@@ -95,30 +212,6 @@ int main() {
           RS232_Print(offon[0]);
           RS232_Print("\n");
           break;
-        case 'S': // Read sequence
-          printAllFrames = 0;
-          RS232_Print("READ SEQUENCE > \n");
-          readSeq = 1;
-          s_len = 0;
-          s_dig = 0;
-          s_c[0] = s_c[1] = 0;
-          break;
-        case 'W': // Send command
-          printAllFrames = 1;
-          readSeq = 0;
-          msg.broadcast = UNICAST;
-          msg.length = s_len;
-          AVCLAN_sendframe(&msg);
-          break;
-        case 'Q': // Send broadcast
-          printAllFrames = 1;
-          readSeq = 0;
-          msg.broadcast = BROADCAST;
-          msg.peripheral_addr = 0x1FF;
-          msg.length = s_len;
-          AVCLAN_sendframe(&msg);
-          msg.peripheral_addr = HU_ADDR;
-          break;
         case 'l': // Print received messages
           printAllFrames ^= 1;
           RS232_Print("Logging: ");
@@ -138,31 +231,43 @@ int main() {
           RS232_Print(offon[muteBus]);
           RS232_Print("\n");
           break;
-        case 'b':
+        case 'E': // Beep
-        case 'B': // Beep
+          out = (AVCLAN_frame_t *)popQueue(&cache);
+          if (out) {
+            resp = (RFrame_t *)popQueue(&rcache);
+            if (resp) {
+              out->broadcast = UNICAST;
+              out->controller_addr = DEVICE_ADDR;
+              out->peripheral_addr = HU_ADDR;
               {
-          const uint8_t beep[] = {0x00, dev_CD_CHANGER, dev_BEEP_SPEAKERS, 0x60,
+                const uint8_t beep[] = {0x00, dev_CD_CHANGER, dev_BEEP_SPEAKERS,
-                                  0x01};
+                                        0x60, 0x01};
-          memcpy(data_tmp, beep, sizeof(beep));
+                out->length = sizeof(beep);
-          msg.length = sizeof(beep);
+                memcpy(out->data, beep, sizeof(beep));
+              }
+              *resp = (RFrame_t){.r = r_Handled, .frame = out};
+              push_or_return_resp(resp);
+            }
           }
-          msg.broadcast = UNICAST;
-          msg.controller_addr = DEVICE_ADDR;
-          msg.peripheral_addr = HU_ADDR;
-          AVCLAN_sendframe(&msg);
           break;
-        case 'p':
+        case 'P':
-          CD_Mode = stPlay;
+          out = (AVCLAN_frame_t *)popQueue(&cache);
+          if (out) {
+            resp = (RFrame_t *)popQueue(&rcache);
+            if (resp) {
+              out->broadcast = UNICAST;
+              out->controller_addr = DEVICE_ADDR;
+              out->peripheral_addr = HU_ADDR;
               {
                 const uint8_t play[] = {0x00,      dev_COMM_CTRL,  dev_COMM_v1,
                                         Insertion, dev_CD_CHANGER, 0x01};
-            memcpy(data_tmp, play, sizeof(play));
+                out->length = sizeof(play);
-            msg.length = sizeof(play);
+                memcpy(out->data, play, sizeof(play));
+              }
+              *resp = (RFrame_t){.r = r_Handled, .frame = out};
+              push_or_return_resp(resp);
+            }
           }
-          msg.broadcast = UNICAST;
-          msg.controller_addr = DEVICE_ADDR;
-          msg.peripheral_addr = HU_ADDR;
-          AVCLAN_sendframe(&msg);
           break;
 
 #ifdef SOFTWARE_DEBUG
@@ -171,52 +276,90 @@ int main() {
 
         case 0x10: // Signals binary sequence incoming
           if (!readSeq && !readBinary) {
+            readSeq = readBinary = 1;
+            seqLen = 0;
+            break;
+          } // otherwise we're reading binary and that's a data byte
+        case 'U': // Send command
+          RS232_Print("READ SEQUENCE (U)> \n");
+          lastPrintAllFrames = printAllFrames;
+          printAllFrames = 0;
           readSeq = 1;
-            readBinary = 1;
+          seqLen = hexDigit = 0;
-            s_len = 0;
+          hexChars[0] = hexChars[1] = 0;
+          seqBroadcast = UNICAST;
+          break;
+        case 'B': // Send broadcast
+          RS232_Print("READ SEQUENCE (B)> \n");
+          lastPrintAllFrames = printAllFrames;
+          printAllFrames = 0;
+          readSeq = 1;
+          seqLen = hexDigit = 0;
+          hexChars[0] = hexChars[1] = 0;
+          seqBroadcast = BROADCAST;
           break;
-          } // else (readSeq || readBinary); fall through to default
         case '\n':
-          if (readSeq && readBinary && data_tmp[s_len] == 0x17) {
+          if (readSeq) {
-            {
+            if (readBinary) {
-              uint8_t tmp[MAXMSGLEN];
+              if (data_tmp[seqLen] == 0x17) {
-              AVCLAN_frame_t frame = {.data = tmp};
+                out = (AVCLAN_frame_t *)popQueue(&cache);
-              err = AVCLAN_parseframe(data_tmp, --s_len, &frame);
+                if (out) {
+                  err = AVCLAN_parseframe(data_tmp, --seqLen, out);
                   if (!err) {
-                AVCLAN_sendframe(frame);
+                    resp = (RFrame_t *)popQueue(&rcache);
-                readSeq = 0;
+                    if (resp) {
-                readBinary = 0;
+                      *resp = (RFrame_t){.r = r_Handled, .frame = out};
+                      push_or_return_resp(resp);
                     }
                   }
+                }
+                readSeq = readBinary = 0;
+              } else
+                goto DEFAULT; // reading binary and this is a real data byte;
+                              // fall through to default
+            } else {
+              out = (AVCLAN_frame_t *)popQueue(&cache);
+              if (out) {
+                resp = (RFrame_t *)popQueue(&rcache);
+                if (resp) {
+                  out->broadcast = seqBroadcast;
+                  out->controller_addr = DEVICE_ADDR;
+                  switch (seqBroadcast) {
+                    case UNICAST: out->peripheral_addr = HU_ADDR; break;
+                    case BROADCAST: out->peripheral_addr = 0x1FF; break;
+                  }
+                  out->length = seqLen;
+                  memcpy(out->data, data_tmp, seqLen);
+                  *resp = (RFrame_t){.r = r_Handled, .frame = out};
+                  push_or_return_resp(resp);
+                }
+              }
+              printAllFrames = lastPrintAllFrames;
+            }
             break;
-          } // else (readSeq || readBinary || most recent char != 0x17);
+          }
-            // fall through to default
+        DEFAULT:
         default:
           if (readSeq) {
             if (readBinary) {
-              data_tmp[s_len++] = readkey;
+              data_tmp[seqLen++] = readkey;
             } else {
-              s_c[s_dig] = readkey;
+              hexChars[hexDigit++] = readkey;
 
-              s_dig++;
+              if (hexDigit == 2) {
-              if (s_dig == 2) {
+                char h, l;
-                if (s_c[0] < ':')
+                h = toupper(hexChars[0]);
-                  s_c[0] -= 48;
+                h += (h < ':') ? 0xd0 : 0xc9; // digit or letter
-                else
+
-                  s_c[0] -= 55;
+                l = toupper(hexChars[1]);
-                data_tmp[s_len] = 16 * s_c[0];
+                l += (l < ':') ? 0xd0 : 0xc9;
-                if (s_c[1] < ':')
+
-                  s_c[1] -= 48;
+                data_tmp[seqLen++] = (h << 4) | l;
-                else
+                hexDigit = hexChars[0] = hexChars[1] = 0;
-                  s_c[1] -= 55;
-                data_tmp[s_len] += s_c[1];
-                s_len++;
-                s_dig = 0;
-                s_c[0] = s_c[1] = 0;
               }
               if (echoCharacters) {
                 RS232_Print("CURRENT SEQUENCE > ");
-                for (i = 0; i < s_len; i++) {
+                for (uint8_t i = 0; i < seqLen; i++) {
                   RS232_PrintHex8(data_tmp[i]);
                   RS232_SendByte(' ');
                 }
@@ -279,14 +422,14 @@ void general_GPIO_init() {
 
 void print_help() {
   RS232_Print("AVCLAN Mockingboard v1\n");
-  RS232_Print("S - read sequence\n"
+  RS232_Print("W - begin reading for unicast message\n"
-              "W - send command\n"
+              "Q - begin reading for broadcast message\n"
-              "Q - send broadcast\n"
               "m - Toggle mute for mockingboard bus activity\n"
               "l - Toggle message logging\n"
               "k - Toggle character echo\n"
-              "X/x - Turn binary ON or OFF, respectively\n"
+              "X/x - Turn binary printing ON or OFF, respectively\n"
-              "B - Beep\n"
+              "E - Beep\n"
+              "P - Play\n"
               "v - Toggle verbose logging\n"
 #ifdef SOFTWARE_DEBUG
               "M - Measure bit-timing (pulse-widths and periods)\n"
@@ -297,3 +440,10 @@ void print_help() {
 #endif
               "? - Print this message\n");
 }
+
+// Periodic interrupt with a 1 sec period; only enabled when playing
+ISR(RTC_PIT_vect) {
+  AVCLAN_incrementTime();
+  enqueueStatus = 1;
+  RTC.PITINTFLAGS = RTC_PI_bm;
+}