ns to us delay

[be80be]

how to make a delay like __delay_ns (800);
In xc8
Could i just put .8 don't think that works

 

[be80be]

Im runing at 64 mhz trying to come up with a delay for ns

Heres the code its for ws2812b leds

/*
 * File:   newmain.c
 * Author: burt
 *
 * Created on March 8, 2025, 3:44 PM
 */

#define _XTAL_FREQ 64000000
#include <xc.h>
#include <stdint.h>
//#include <libpic30.h> // For delay functions

// Configuration bits for PIC18F25Q10 (adjust as needed)
#pragma config FEXTOSC = OFF, RSTOSC = HFINTOSC_64MHZ // Use internal 64MHz oscillator
#pragma config CLKOUTEN = OFF, CSWEN = ON, FCMEN = ON
#pragma config MCLRE = ON, PWRTE = OFF, WDTE = OFF, LPBOREN = OFF, BOREN = OFF
#pragma config LVP = OFF, PPS1WAY = ON, STVREN = ON, DEBUG = OFF
#pragma config WRT = OFF, CP = OFF, CPD = OFF

#define WS2812_PIN LATCbits.LATC0 // Use RC0 for WS2812B data
#define WS2812_TRIS TRISCbits.TRISC0

// Timing constants (adjust if needed, based on 64MHz clock)
//#define T0H 350 // Time high for 0 bit (ns)
//#define T0L 900 // Time low for 0 bit (ns)
//#define T1H 800 // Time high for 1 bit (ns)
//#define T1L 450 // Time low for 1 bit (ns)
//#define RESET_TIME 55 // Reset time in microseconds

#define NUM_LEDS 30 // Number of LEDs
uint8_t ledData[NUM_LEDS * 3]; // RGB data

void sendBit(uint8_t bit) {
    WS2812_PIN = 1;
    if (bit) {
        __delay_ns(800);
        WS2812_PIN = 0;
        __delay_ns(450);
    } else {
        __delay_ns(350);
        WS2812_PIN = 0;
        __delay_ns(900);
    }
}

void sendByte(uint8_t byte) {
    for (int i = 7; i >= 0; i--) {
        sendBit((byte >> i) & 1);
    }
}

void sendLEDData() {
    for (int i = 0; i < NUM_LEDS * 3; i++) {
        sendByte(ledData[i]);
    }
    __delay_us(55);
}

void main(void) {
    // Oscillator setup (if needed, but 64MHz is set in config)
    // OSCCON1 = 0x60; // Select HFINTOSC (already in config)

    WS2812_TRIS = 0; // Set RC0 as output

    // Initialize LED data (example: red, green, blue pattern)
    for (int i = 0; i < NUM_LEDS; i++) {
        if(i%3 == 0){ledData[i * 3] = 255; ledData[i * 3 + 1] = 0; ledData[i * 3 + 2] = 0;} //red
        else if (i%3 == 1){ledData[i * 3] = 0; ledData[i * 3 + 1] = 255; ledData[i * 3 + 2] = 0;} //green
        else{ledData[i * 3] = 0; ledData[i * 3 + 1] = 0; ledData[i * 3 + 2] = 255;} //blue
    }

    while (1) {
        sendLEDData();
        __delay_ms(20); // Delay between frames
    }
}

 

[be80be]

this did build

/*
 * File:   newmain.c
 * Author: burt
 *
 * Created on March 8, 2025, 3:44 PM
 */

#define _XTAL_FREQ 64000000
#include <xc.h>
#include <stdint.h>
//#include <libpic30.h> // For delay functions

// Configuration bits for PIC18F25Q10 (adjust as needed)
#pragma config FEXTOSC = OFF, RSTOSC = HFINTOSC_64MHZ // Use internal 64MHz oscillator
#pragma config CLKOUTEN = OFF, CSWEN = ON, FCMEN = ON
#pragma config MCLRE = EXTMCLR, PWRTE = OFF, WDTE = OFF, LPBOREN = OFF, BOREN = OFF
#pragma config LVP = OFF, PPS1WAY = ON, STVREN = ON
#pragma config CP = OFF, CPD = OFF
#pragma config WRT0 = OFF       // Write Protection Block 0 (Block 0 (000800-001FFFh) not write-protected)
#pragma config WRT1 = OFF       // Write Protection Block 1 (Block 1 (002000-003FFFh) not write-protected)
#pragma config WRT2 = OFF       // Write Protection Block 2 (Block 2 (004000-005FFFh) not write-protected)
#pragma config WRT3 = OFF       // Write Protection Block 3 (Block 3 (006000-007FFFh) not write-protected)

#define WS2812_PIN LATCbits.LATC0 // Use RC0 for WS2812B data
#define WS2812_TRIS TRISCbits.TRISC0

// Timing constants (adjust if needed, based on 64MHz clock)
//#define T0H 350 // Time high for 0 bit (ns)
//#define T0L 900 // Time low for 0 bit (ns)
//#define T1H 800 // Time high for 1 bit (ns)
//#define T1L 450 // Time low for 1 bit (ns)
//#define RESET_TIME 55 // Reset time in microseconds

#define NUM_LEDS 30 // Number of LEDs
uint8_t ledData[NUM_LEDS * 3]; // RGB data

void sendBit(uint8_t bit) {
    WS2812_PIN = 1;
    if (bit) {
        __delay_ms(.8);
        WS2812_PIN = 0;
        __delay_ms(.45);
    } else {
        __delay_ms(.35);
        WS2812_PIN = 0;
        __delay_ms(.9);
    }
}

void sendByte(uint8_t byte) {
    for (int i = 7; i >= 0; i--) {
        sendBit((byte >> i) & 1);
    }
}

void sendLEDData() {
    for (int i = 0; i < NUM_LEDS * 3; i++) {
        sendByte(ledData[i]);
    }
    __delay_us(55);
}

void main(void) {
    // Oscillator setup (if needed, but 64MHz is set in config)
    // OSCCON1 = 0x60; // Select HFINTOSC (already in config)
    ANSELCbits.ANSELC0 = 0;
    WS2812_TRIS = 0; // Set RC0 as output

    // Initialize LED data (example: red, green, blue pattern)
    for (int i = 0; i < NUM_LEDS; i++) {
        if(i%3 == 0){ledData[i * 3] = 255; ledData[i * 3 + 1] = 0; ledData[i * 3 + 2] = 0;} //red
        else if (i%3 == 1){ledData[i * 3] = 0; ledData[i * 3 + 1] = 255; ledData[i * 3 + 2] = 0;} //green
        else{ledData[i * 3] = 0; ledData[i * 3 + 1] = 0; ledData[i * 3 + 2] = 255;} //blue
    }

    while (1) {
        sendLEDData();
        __delay_ms(20); // Delay between frames
    }
}

 

[ZipZapOuch]

You can just execute about 12
NOP();
Instructions and you'll have your 800nSec delay (do the math, this is an estimate for four clock cycles per instruction at 64MHz

 

[be80be]

That’s to easy I’d miss every one reply’s
13 is closer libpic30.h has __delay_ns was hoping for something like it.

 

[rjenkinsgb]

I have a work-in-progress neopixels style driver that may help;

I was formatting the data bytes up to padded 32 bit values, then use SPI to DMA blast it to the LEDs.

//
// Convert a byte to neopixel format
//
void repack(uint32_t *outbits, int8_t inp) {
    //
    //
    uint32_t *pixbits;
    int8_t val;
    pixbits = outbits;
    val = inp;
        
    *pixbits = 0x88888888L;
        
    if(val & 0x01) *pixbits |= 0x00000004L;
    if(val & 0x02) *pixbits |= 0x00000040L;
    if(val & 0x04) *pixbits |= 0x00000400L;
    if(val & 0x08) *pixbits |= 0x00004000L;
    if(val & 0x10) *pixbits |= 0x00040000L;
    if(val & 0x20) *pixbits |= 0x00400000L;
    if(val & 0x40) *pixbits |= 0x04000000L;
    if(val & 0x80) *pixbits |= 0x40000000L;
        
}

Using ping-pong buffering, so two buffer sets, one for loading and one for output. With the CCS compiler I use, a DMA output is a single line instruction. There is also a function to check when that is complete.

//
        // ping-pong buffer system;
        // exchange input and output buffers each time through.
        bufsel++;
        
        if(bufsel & 1) {
            b_set = buffer_b;
            b_out = buffer_a;
        }
        else {
            b_set = buffer_a;
            b_out = buffer_b;
        }
        
        
        // Send last updated buffer
        spi_transfer_write(b_out, cbytes);

I'm aiming for smooth animation speeds on large strings or arrays..
The MCU is a DSPIC33E series, so lots of RAM available.

A similar routine could be used to output one pixel worth at a time though, using SPI to send one pixel while preparing the next.

 

[Ian Rogers]

for a clock of 62.5nS

I would just shift a dummy int 12 or 13 times...
X<<=13;

 

[Nigel Goodwin]

I imagine if you're wanting nS delays, then ASM is the way to go, as you don't really know what the C compiler is going to do with the code - particularly with the free version of XC8.

You've also got the added issue of the surrounding code, calling and returning from the delay - which could easily mess it up.

However, there's example code for NeoPixels at MicroChip, using the CLC - I've used that for various PIC processors and all have worked fine - which just very minor tweaks.

Here's a YouTube video: