ThroughSerial

ThroughSerial

Medium	Pins used	Inclusion
Wires	2	#include <PJONThroughSerial.h>

With ThroughSerial strategy, PJON can run through a software or hardware Serial port working out of the box with many Arduino compatible serial transceivers, like RS485 or radio modules like HC-12 (HCMODU0054). It complies with TSDL v3.0.

This strategy is based upon the obsolete blocking implementation although reception is now asynchronous and completely non-blocking. It is not required to call bus.receive() with any delay, just call it frequently to see if there are any packets that have been received.

Why PJON over Serial?

Serial communication is fast and reliable but it is often useless without all the features PJON contains. ThroughAsyncSerial has been developed to enable PJON communication through a serial data link. Adding PJON on top of Serial it is possible to leverage of the PJON protocol layer features like acknowledge, addressing, multiplexing, packet handling, 8 or 32-bit CRC and traffic control.

ThroughSerial has been developed primarily to be used in master-slave mode. ThroughSerial in multi-master mode, being unable to detect or avoid collisions, operates using the slotted ALOHA medium access method. Of all contention based random multiple access methods, slotted ALOHA, which maximum data throughput is only 36.8% of the available bandwidth, is one of the least efficient and should not be applied in networks where many devices often need to arbitrarily transmit data.

ThroughSerial performs well if used with ESP8266 and ESP32 where blocking procedures can strongly degrade functionality. The reception phase is entirely non-blocking. Sending and acknowledgement however are still blocking.

Configuration

Before including the library it is possible to configure ThroughSerial using predefined constants:

Constant	Purpose	Supported value
TS_READ_INTERVAL	minimum interval between receptions	Duration in microseconds (100 by default)
TS_BYTE_TIME_OUT	Maximum byte reception time-out	Duration in microseconds (1000000 by default)
TS_RESPONSE_TIME_OUT	Maximum response time-out	Duration in microseconds (45000 by default)
TS_BACK_OFF_DEGREE	Maximum back-off exponential degree	Numeric value (4 by default)
TS_MAX_ATTEMPTS	Maximum transmission attempts	Numeric value (20 by default)

Use PJONThroughSerial to instantiate a PJON object ready to communicate using ThroughSerial strategy:

#include <PJONThroughSerial.h>
PJONThroughSerial bus;

Call the begin method on the Serial or SoftwareSerial object you want to use for PJON communication and pass it to the set_serial method:

#include <PJONThroughSerial.h>
PJONThroughSerial bus;

void setup() {
  Serial.begin(9600);
  bus.strategy.set_serial(&Serial);
}

There is a default reception interval of 100 microseconds used to allow data to accumulate in the hardware UART buffer. This value is configurable using bus.strategy.set_read_interval(100) passing an arbitrary interval in microseconds. The read interval may require adjustment depending on UART RX buffer size and baud rate.

bus.strategy.set_read_interval(100);

For a simple use with RS485 serial modules a transmission enable pin setter has been added:

bus.strategy.set_enable_RS485_pin(11);

If separate enable setters are needed use:

// Set RS485 reception enable pin
bus.strategy.set_RS485_rxe_pin(11);
// Set RS485 transmission enable pin
bus.strategy.set_RS485_txe_pin(12);

See the Blink and BlinkWithResponse examples, if you need to interface devices using RS485 see the RS485-Blink example. HC-12 wireless module supports the synchronous acknowledgement, see HC-12-Blink, HC-12-SendAndReceive and HC-12-LocalChat examples.

All the other necessary information is present in the general Documentation.

Known issues

• Transmission is still blocking, will be made non-blocking in the next versions.
• acknowledgement procedure is still blocking, will be made non-blocking in the next versions.