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Size the SoftwareSerial ISR edge buffer independently of the byte buffer #1264

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Size the SoftwareSerial ISR edge buffer independently of the byte buffer #1264

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16 changes: 15 additions & 1 deletion src/PassiveMeterCommunicator.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,15 @@

#include "PassiveMeterCommunicator.h"

// Multiplier for the SoftwareSerial ISR edge buffer relative to the byte
// buffer. 4 gives ~0.4 s of slack at 2400 baud 8E1 for 4 x 64 x 4 B = 1 kB
// extra heap with the default 64 byte buffer. The library's own default is
// (2 + data bits + parity), i.e. 11 for 8E1, but that costs 11 kB with a
// 256 byte buffer, too much on ESP8266. Override with -D SWSERIAL_ISR_BUFFER_FACTOR=n.
#ifndef SWSERIAL_ISR_BUFFER_FACTOR
#define SWSERIAL_ISR_BUFFER_FACTOR 4
#endif

const uint32_t AUTO_BAUD_RATES[] = { 2400, 9600, 115200 };
const uint8_t AUTO_BAUD_RATES_COUNT = sizeof(AUTO_BAUD_RATES) / sizeof(AUTO_BAUD_RATES[0]);
#include "IEC6205675.h"
Expand Down Expand Up @@ -779,7 +788,12 @@ void PassiveMeterCommunicator::setupHanPort(uint32_t baud, uint8_t parityOrdinal
if (debugger->isActive(RemoteDebug::DEBUG))
#endif
debugger->printf_P(PSTR("Using serial buffer size %d\n"), 64 * bufferSize);
swSerial->begin(baud, serialConfig, rxpin, txpin, invert, meterConfig.bufferSize * 64, meterConfig.bufferSize * 64);
// The second capacity is the ISR edge buffer: one entry per bit
// transition, so up to (2 + data bits + parity) entries per byte.
// Sizing it equal to the byte buffer leaves room for only ~25 bytes
// of pending data at 8E1, which overflows as soon as loop() is held
// up for ~0.1 s at 2400 baud (web requests, MQTT publish, LittleFS).
swSerial->begin(baud, serialConfig, rxpin, txpin, invert, meterConfig.bufferSize * 64, meterConfig.bufferSize * 64 * SWSERIAL_ISR_BUFFER_FACTOR);
hanSerial = swSerial;
hwSerial = NULL;
#else
Expand Down
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