PulseIn time correction required using a RAK4631

[TersaCA]

Operating System

Linux

IDE version

2.3.4

Board

RAK4630/4631

BSP version

1.3.3

Sketch

In a RAK Wireless example, usings a ultasonic module, they use a correction factor (0.7726) for the time returned by PulseIn.

`
digitalWrite(TRIG, LOW);
pinMode(ECHO, INPUT);
respondTime = pulseIn(ECHO, HIGH); // microseconds
delay(33);

if(RAK4631_BOARD)
{
respondTime = respondTime*0.7726; // Time calibration factor is 0.7726,to get real time microseconds for 4631board
}
Serial.printf("respond time is %d\r\n",respondTime);`

I asked them why their module needed a correction. They check the example and the correction is need with the RAK4530/4631, but they had no idea why the adafruit function returned the wrong time for their nrf52.

I looked at the adafruit code in;

PulseIn

countPulseASM

I don't fully understand the ASM timing code, but i find all the references to SAMD compilation and directives a little strange.

`using the command line:

arm-none-eabi-gcc -mcpu=cortex-m0plus -mthumb -c -Os -W -ffunction-sections -fdata-sections \
                  -nostdlib --param max-inline-insns-single=500 -fno-exceptions -MMD \
                  -DF_CPU=48000000L -DARDUINO=10602 -DARDUINO_SAMD_ZERO -DARDUINO_ARCH_SAMD \
                  -D__SAMD21G18A__ -DUSB_VID=0x2341 -DUSB_PID=0x004d -DUSBCON \
                  -DUSB_MANUFACTURER="Arduino LLC" -DUSB_PRODUCT="Arduino Zero" \
                  -I/Code/arduino/build/linux/work/hardware/tools/CMSIS/CMSIS/Include/ \
                  -I/Code/arduino/build/linux/work/hardware/tools/CMSIS/Device/ATMEL/ \
                  -I/Code/arduino/build/linux/work/hardware/arduino/samd/cores/arduino \
                  -I/Code/arduino/build/linux/work/hardware/arduino/samd/variants/arduino_zero \
                  count.c -Wa,-ahlmsd=output.lst -dp -fverbose-asm -S

The result has been slightly edited to increase readability.`

What happened ?

How to reproduce ?

Run example:
https://github.com/RAKWireless/WisBlock/blob/master/examples/common/IO/RAK12007_OLED_Show_Distance/RAK12007_OLED_Show_Distance.ino

using RAK4631 and RAK baseboard and RAK12007 ultrasound.

Debug Log

No response

Screenshots

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