🎨 MMU2 cleanup

Marlin/src/feature/mmu/mmu2.cpp

 #define MMU_CMD_TIMEOUT 45000UL // 45s timeout for mmu commands (except P0)
 #define MMU_P0_TIMEOUT 3000UL   // Timeout for P0 command: 3seconds
 
-#define MMU2_COMMAND(S) tx_str(F(S "\n"))
+#define MMU2_SEND(S) tx_str(F(S "\n"))
+#define MMU2_RECV(S) rx_str(F(S "\n"))
 
 #if ENABLED(MMU_EXTRUDER_SENSOR)
   uint8_t mmu_idl_sens = 0;
     safe_delay(20);
     WRITE(MMU2_RST_PIN, HIGH);
   #else
-    MMU2_COMMAND("X0"); // Send soft reset
+    MMU2_SEND("X0");  // Send soft reset
   #endif
 }
 
     case -1:
       if (rx_start()) {
         prev_P0_request = millis();   // Initialize finda sensor timeout
-
         DEBUG_ECHOLNPGM("MMU => 'start'");
         DEBUG_ECHOLNPGM("MMU <= 'S1'");
-
-        MMU2_COMMAND("S1");   // Read Version
+        MMU2_SEND("S1");    // Read Version
         state = -2;
       }
       else if (millis() > 30000) { // 30sec after reset disable MMU
     case -2:
       if (rx_ok()) {
         sscanf(rx_buffer, "%huok\n", &version);
-
         DEBUG_ECHOLNPGM("MMU => ", version, "\nMMU <= 'S2'");
-
-        MMU2_COMMAND("S2");   // Read Build Number
+        MMU2_SEND("S2");    // Read Build Number
         state = -3;
       }
       break;
 
         #if ENABLED(MMU2_MODE_12V)
           DEBUG_ECHOLNPGM("MMU <= 'M1'");
-
-          MMU2_COMMAND("M1");   // Stealth Mode
+          MMU2_SEND("M1");    // Stealth Mode
           state = -5;
 
         #else
           DEBUG_ECHOLNPGM("MMU <= 'P0'");
-
-          MMU2_COMMAND("P0");   // Read FINDA
+          MMU2_SEND("P0");    // Read FINDA
           state = -4;
         #endif
       }
       // response to M1
       if (rx_ok()) {
         DEBUG_ECHOLNPGM("MMU => ok");
-
         DEBUG_ECHOLNPGM("MMU <= 'P0'");
-
-        MMU2_COMMAND("P0");   // Read FINDA
+        MMU2_SEND("P0");    // Read FINDA
         state = -4;
       }
       break;
         else if (cmd == MMU_CMD_C0) {
           // continue loading
           DEBUG_ECHOLNPGM("MMU <= 'C0'");
-          MMU2_COMMAND("C0");
+          MMU2_SEND("C0");
           state = 3; // wait for response
         }
         else if (cmd == MMU_CMD_U0) {
           // unload current
           DEBUG_ECHOLNPGM("MMU <= 'U0'");
-
-          MMU2_COMMAND("U0");
+          MMU2_SEND("U0");
           state = 3; // wait for response
         }
         else if (WITHIN(cmd, MMU_CMD_E0, MMU_CMD_E0 + EXTRUDERS - 1)) {
         else if (cmd == MMU_CMD_R0) {
           // recover after eject
           DEBUG_ECHOLNPGM("MMU <= 'R0'");
-          MMU2_COMMAND("R0");
+          MMU2_SEND("R0");
           state = 3; // wait for response
         }
         else if (WITHIN(cmd, MMU_CMD_F0, MMU_CMD_F0 + EXTRUDERS - 1)) {
         cmd = MMU_CMD_NONE;
       }
       else if (ELAPSED(millis(), prev_P0_request + 300)) {
-        MMU2_COMMAND("P0"); // Read FINDA
+        MMU2_SEND("P0");  // Read FINDA
         state = 2; // wait for response
       }
 
         if (mmu_idl_sens) {
           if (FILAMENT_PRESENT() && mmu_loading_flag) {
             DEBUG_ECHOLNPGM("MMU <= 'A'");
-            MMU2_COMMAND("A"); // send 'abort' request
+            MMU2_SEND("A");   // send 'abort' request
             mmu_idl_sens = 0;
             DEBUG_ECHOLNPGM("MMU IDLER_SENSOR = 0 - ABORT");
           }
           const bool keep_trying = !mmu2s_triggered && last_cmd == MMU_CMD_C0;
           if (keep_trying) {
             // MMU ok received but filament sensor not triggered, retrying...
-            DEBUG_ECHOLNPGM("MMU => 'ok' (filament not present in gears)");
+            DEBUG_ECHOLNPGM("MMU => 'ok' (no filament in gears)");
             DEBUG_ECHOLNPGM("MMU <= 'C0' (keep trying)");
-            MMU2_COMMAND("C0");
+            MMU2_SEND("C0");
           }
         #else
           constexpr bool keep_trying = false;
  */
 bool MMU2::rx_start() {
   // check for start message
-  return rx_str(F("start\n"));
+  return MMU2_RECV("start");
 }
 
 /**
  * Check if we received 'ok' from MMU
  */
 bool MMU2::rx_ok() {
-  if (rx_str(F("ok\n"))) {
+  if (MMU2_RECV("ok")) {
     prev_P0_request = millis();
     return true;
   }
         // When (T0 rx->ok) load is ready, but in fact it did not load
         // successfully or an overload created pressure in the extruder.
         // Send (C0) to load more and move E_AXIS a little to release pressure.
-        if ((fil_present = FILAMENT_PRESENT())) MMU2_COMMAND("A");
+        if ((fil_present = FILAMENT_PRESENT())) MMU2_SEND("A");
       } while (!fil_present && PENDING(millis(), expire_ms));
       stepper.disable_extruder();
       manage_response(true, true);
     if (cmd == MMU_CMD_NONE && last_cmd == MMU_CMD_C0) {
       if (present && !mmu2s_triggered) {
         DEBUG_ECHOLNPGM("MMU <= 'A'");
-        tx_str(F("A\n"));
+        MMU2_SEND("A");
       }
       // Slowly spin the extruder during C0
       else {