Serial store & forward

utility/SerialFirmata.cpp

@@ -14,11 +14,19 @@
 
   - handlePinMode calls Firmata::setPinMode
 
-  Last updated October 16th, 2016
+  Last updated March 16th, 2020
 */
 
 #include "SerialFirmata.h"
 
+// The RX and TX hardware FIFOs of the ESP8266 hold 128 bytes that can be 
+// extended using interrupt handlers. The Arduino constants are not available
+// for the ESP8266 platform.
+#if !defined(SERIAL_RX_BUFFER_SIZE) && defined(UART_TX_FIFO_SIZE)
+#define SERIAL_RX_BUFFER_SIZE UART_TX_FIFO_SIZE
+#endif
+
+
 SerialFirmata::SerialFirmata()
 {
 #if defined(SoftwareSerial_h)
@@ -29,6 +37,12 @@ SerialFirmata::SerialFirmata()
 #endif
 
   serialIndex = -1;
+
+#if defined(FIRMATA_SERIAL_RX_DELAY)
+  for (byte i = 0; i < SERIAL_READ_ARR_LEN; i++) {
+    maxRxDelay[i] = FIRMATA_SERIAL_RX_DELAY; // @todo provide setter
+  }
+#endif
 }
 
 boolean SerialFirmata::handlePinMode(byte pin, int mode)
@@ -56,13 +70,17 @@ boolean SerialFirmata::handleSysex(byte command, byte argc, byte *argv)
     Stream *serialPort;
     byte mode = argv[0] & SERIAL_MODE_MASK;
     byte portId = argv[0] & SERIAL_PORT_ID_MASK;
+    if (portId >= SERIAL_READ_ARR_LEN) return false;
 
     switch (mode) {
       case SERIAL_CONFIG:
         {
           long baud = (long)argv[1] | ((long)argv[2] << 7) | ((long)argv[3] << 14);
           serial_pins pins;
-
+#if defined(FIRMATA_SERIAL_RX_DELAY)
+          lastBytesAvailable[portId] = 0;
+          lastBytesReceived[portId] = 0;
+#endif
           if (portId < 8) {
             serialPort = getPortFromId(portId);
             if (serialPort != NULL) {
@@ -229,6 +247,10 @@ void SerialFirmata::reset()
   serialIndex = -1;
   for (byte i = 0; i < SERIAL_READ_ARR_LEN; i++) {
     serialBytesToRead[i] = 0;
+#if defined(FIRMATA_SERIAL_RX_DELAY)
+    lastBytesAvailable[i] = 0;
+    lastBytesReceived[i] = 0;    
+#endif
   }
 }
 
@@ -302,6 +324,10 @@ void SerialFirmata::checkSerial()
 
   if (serialIndex > -1) {
 
+#if defined(FIRMATA_SERIAL_RX_DELAY)
+    unsigned long currentMillis = millis();
+#endif
+
     // loop through all reporting (READ_CONTINUOUS) serial ports
     for (byte i = 0; i < serialIndex + 1; i++) {
       portId = reportSerial[i];
@@ -316,27 +342,53 @@ void SerialFirmata::checkSerial()
         continue;
       }
 #endif
-      if (serialPort->available() > 0) {
-        Firmata.write(START_SYSEX);
-        Firmata.write(SERIAL_MESSAGE);
-        Firmata.write(SERIAL_REPLY | portId);
-
-        if (bytesToRead == 0 || (serialPort->available() <= bytesToRead)) {
-          numBytesToRead = serialPort->available();
+      int bytesAvailable = serialPort->available();
+      if (bytesAvailable > 0) {
+#if defined(FIRMATA_SERIAL_RX_DELAY)
+        if (bytesAvailable > lastBytesAvailable[portId]) {
+          lastBytesReceived[portId] = currentMillis;
+        }
+        lastBytesAvailable[portId] = bytesAvailable;
+#endif
+        if (bytesToRead <= 0 || (bytesAvailable <= bytesToRead)) {
+          numBytesToRead = bytesAvailable;
         } else {
           numBytesToRead = bytesToRead;
         }
-
+#if defined(FIRMATA_SERIAL_RX_DELAY)
+        if (maxRxDelay[portId] >= 0 && numBytesToRead > 0) {
+          // read and send immediately only if
+          // - expected bytes are unknown and the receive buffer has reached 50 %
+          // - expected bytes are available
+          // - maxRxDelay has expired since last receive (or time counter wrap)
+          if (!((bytesToRead <= 0 && bytesAvailable >= SERIAL_RX_BUFFER_SIZE/2)
+             || (bytesToRead > 0 && bytesAvailable >= bytesToRead)
+             || (maxRxDelay[portId] > 0 && (currentMillis < lastBytesReceived[portId] || (currentMillis - lastBytesReceived[portId]) >= maxRxDelay[portId])))) {
+            // delay
+            numBytesToRead = 0;
+          }
+        }
+#endif
         // relay serial data to the serial device
-        while (numBytesToRead > 0) {
-          serialData = serialPort->read();
-          Firmata.write(serialData & 0x7F);
-          Firmata.write((serialData >> 7) & 0x7F);
-          numBytesToRead--;
+        if (numBytesToRead > 0) {
+#if defined(FIRMATA_SERIAL_RX_DELAY)
+          lastBytesAvailable[portId] -= numBytesToRead;
+#endif
+          Firmata.write(START_SYSEX);
+          Firmata.write(SERIAL_MESSAGE);
+          Firmata.write(SERIAL_REPLY | portId);
+
+          // relay serial data to the serial device
+          while (numBytesToRead > 0) {
+            serialData = serialPort->read();
+            Firmata.write(serialData & 0x7F);
+            Firmata.write((serialData >> 7) & 0x7F);
+            numBytesToRead--;
+          }
+
+          Firmata.write(END_SYSEX);
         }
-        Firmata.write(END_SYSEX);
       }
-
     }
   }
 }

utility/SerialFirmata.h

@@ -15,7 +15,7 @@
   - Defines FIRMATA_SERIAL_FEATURE (could add to Configurable version as well)
   - Imports Firmata.h rather than ConfigurableFirmata.h
 
-  Last updated October 16th, 2016
+  Last updated March 11th, 2020
 */
 
 #ifndef SerialFirmata_h
@@ -30,6 +30,32 @@
 #include <SoftwareSerial.h>
 #endif
 
+// If defined and set to a value between 0 and 255 milliseconds the received bytes
+// will be not be read until until one of the following conditions are met:
+// 1) the expected number of bytes have been received
+// 2) the serial receive buffer is filled to 50 % (default size is 64 bytes)
+// 3) the delay since the last received byte exceeds the configured FIRMATA_SERIAL_RX_DELAY
+//    hints: 5 bytes at 9600 baud take 5 ms, human perception of a delay starts at 50 ms
+// This feature can significantly reduce the load on the transport layer when
+// the byte receive rate is equal or lower than the average Firmata main loop execution
+// duration by preventing single byte transmits if the underlying Firmata stream supports
+// transmit buffering (currently only available with EthernetClientStream). The effect
+// can be increased with higher values of FIRMATA_SERIAL_RX_DELAY.
+// Notes
+// 1) Enabling this feature will delay the received data and may concatenate
+//    bytes into one transmit that would otherwise be transmitted separately.
+// 2) The usefulness and configuration of this feature depends on the baud rate and the serial message type:
+//    a) continuous streaming at higher baud rates: enable but set to 0 (receive buffer store & forward)
+//    b) messages: set to a value below min. inter message delay (message store & forward)
+//    c) continuous streaming at lower baud rates or random characters: undefine or set to -1 (disable)
+// 3) Smaller delays may not have the desired effect, especially with less powerful CPUs, 
+//    if set to a value near or below the average Firmata main loop duration.
+// 4) The Firmata stream write buffer size must be equal or greater than the max. 
+//    serial buffer/message size and the Firmata frame size (4 bytes) to prevent fragmentation
+//    on the transport layer.
+//#define FIRMATA_SERIAL_RX_DELAY 50 // [ms]
+#define FIRMATA_SERIAL_RX_DELAY 50
+
 #define FIRMATA_SERIAL_FEATURE
 
 // Serial port Ids
@@ -194,6 +220,12 @@ class SerialFirmata: public FirmataFeature
     int serialBytesToRead[SERIAL_READ_ARR_LEN];
     signed char serialIndex;
 
+#if defined(FIRMATA_SERIAL_RX_DELAY)
+    byte maxRxDelay[SERIAL_READ_ARR_LEN];
+    int lastBytesAvailable[SERIAL_READ_ARR_LEN];
+    unsigned long lastBytesReceived[SERIAL_READ_ARR_LEN];
+#endif
+
 #if defined(SoftwareSerial_h)
     Stream *swSerial0;
     Stream *swSerial1;