This repository contains Arduino code (arduino-barcodes) for generating TTL barcodes that can be used to synchronize multiple data sources.
The code has been modified from open-ephys/sync-barcodes.
The modifications from the original code include:
- Simultaneous output on multiple pins using "direct port access" (see also section below).
- Barcode settings (barcode duration, inter-barcode interval, number of bits, initiation pulse duration, etc.) can now be easily changed to your preference.
- Several comments have been added for clarity.
Read more about synchronizing multiple data streams:
https://open-ephys.github.io/gui-docs/User-Manual/Plugins/NIDAQmx.html
N.B. the way port manipulation is implemented depends on the exact microcontroller used by the board. In this case I used Arduino Due, whose microcontroller is SAM3X. With other boards things could work differently (e.g. it will certainly be different for ATmega8 and ATmega168). So what is written here https://www.arduino.cc/en/Reference/PortManipulation does not apply to Arduino Due!
If you use
digitalWrite(OUTPUT_PIN_1, HIGH);
digitalWrite(OUTPUT_PIN_2, HIGH);
digitalWrite(OUTPUT_PIN_3, HIGH);
there will be about 2.5 us (microseconds) of delay between one output and the next one.
Synchronous output on multiple pins can be obtained using "port manipulation".
Take the pinout scheme of the Arduino Due board. You must choose pin numbers that converge to the same port. For example, pins 25-30 on Arduino Due map onto port D.
To initialize the pins:
int OUTPUT_PIN_1 = 25; //PD0
int OUTPUT_PIN_2 = 27; //PD2
int OUTPUT_PIN_3 = 29; //PD6
void setup() {
pinMode(OUTPUT_PIN_1, OUTPUT); // initialize digital pin (this line is here only for code clarity, not necessary because we use direct port access)
pinMode(OUTPUT_PIN_2, OUTPUT); // initialize digital pin (this line is here only for code clarity, not necessary because we use direct port access)
pinMode(OUTPUT_PIN_3, OUTPUT); // initialize digital pin (this line is here only for code clarity, not necessary because we use direct port access)
REG_PIOD_OWER = 0b00000000000000000000000001000101;
REG_PIOD_OER = 0b00000000000000000000000001000101;
pinMode lines are not needed, but we keep them just to make the code more readable.
REG_PIOX_OWER and REG_PIOX_OER with X = A, B, C, D, E.
PIO_OWER: PIO (Parallel Input Output) Output Write Enable Register - write 1's here to set the pins you want to enable.
PIO_OER: PIO (Parallel Input Output) Controller Output Enable Register - write 1's here to set pins as OUTPUT.
After 0b there are 32 bits (each port in this microcontroller is 32 bits). The first bit on the right corresponds to port pin 0, increasing leftward.
So by using REG_PIOD_OER = 0b00000000000000000000000001000101; we set PD0, PD2, and PD6 as output pins.
Then, within loop(), just use REG_PIOX_ODSR, instead of digitalWrite
REG_PIOD_ODSR = 0b00000000000000000000000001000101; // sets PD0, PD2, PD6 to HIGH
...
REG_PIOD_ODSR = 0b00000000000000000000000000000000; // sets PD0, PD2, PD6 to LOW
PIO_ODSR allows synchronous writing of the lines in the port (for more info, see 31.5.5 of SAM3X datasheet).
- https://arduino.stackexchange.com/questions/9117/sam3x8e-arduino-due-pin-io-registers (useful)
- https://forum.arduino.cc/index.php?topic=537165.0
- https://forum.arduino.cc/index.php?topic=129868.30
- https://forum.arduino.cc/index.php?topic=260731.0
- https://forum.arduino.cc/index.php?topic=394428.0 (maybe this useful)
- http://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-11057-32-bit-Cortex-M3-Microcontroller-SAM3X-SAM3A_Datasheet.pdf (section 31)