Merge pull request #93 from emeb/master

Update Systick example README and remove redundant Systick millis example

examples/systick_irq/README.md

@@ -4,11 +4,11 @@ interrupts for timing. Many bare-metal and RTOS based embedded applications will
 use the Systick IRQ for timing, periodic housekeeping and task arbitration so
 knowing how to set that up is useful.
 
-Note that this example is *NOT* compatible with the Delay_*() functions that are
-part of the ch32v003fun library - those functions use the Systick counter for
-doing busy-wait delays and assume that the CNT register rolls over at 32-bit
-maximum. Do not use the built-in Delay_Ms() and related functions when using
-Systick for IRQs.
+This code is compatible with the busywait delay functions in the ch32v003fun
+library because it allows the Systick CNT register to keep running over its full
+32-bit range. It does not set the STRE bit in the CTRL register so the counter
+does not reset when the CMP register matches. In order to do this, the CMP register
+is advanced at every IRQ.
 
 Note also the use of the  `__attribute__((interrupt))` syntax in declaring the
 IRQ handler. Some of the IRQ examples from the WCH HAL library have slightly

examples/systick_irq_millis/Makefile

-all : flash
-
-TARGET:=systick_irq_millis
-
-CFLAGS+=-DSTDOUT_UART
-
-include ../../ch32v003fun/ch32v003fun.mk
-
-flash : cv_flash
-clean : cv_clean
-

examples/systick_irq_millis/README.md

-# Systick IRQ demonstration
-This example shows how to set up the built-in Systick IRQ to generate periodic
-interrupts for timing. Many bare-metal and RTOS based embedded applications will
-use the Systick IRQ for timing, periodic housekeeping and task arbitration so
-knowing how to set that up is useful.
-
-Systick.h now also contains an arduino-like millis() function to return the
-current time.
-The example has been adapted to use this millis() function for a lock-free program.
-Here, you compare the difference of current time and the last time a task was
-executed against a desired interval. If enough time has passed, run the next
-step.
-
-The benefit of this dance is that the CPU doesn't spend 250ms (12,000,000
-cycles!) drooling onto the carpet.
-Other important tasks (reading buttons, DDoSing your grandma) can run until it's time.
-
-Of course a real RTos would be much more powerful.
-
-Note that this example is *NOT* compatible with the Delay_Ms() function that's
-part of the ch32v003fun library - that function uses the Systick counter for
-doing busy-wait delays and will interfere with its use in generating predictable
-IRQs. Do not use the built-in Delay_Ms() and related functions when using Systick
-for IRQs.
-
-Note also the use of the  `__attribute__((interrupt))` syntax in declaring the
-IRQ handler. Some of the IRQ examples from the WCH HAL library have slightly
-different syntax to make use of a fast IRQ mode but which is not compatible with
-generic RISC-V GCC so that feature is not used here.
-
-# Use
-Connect LEDs (with proper current limit resistors) to GPIO pins C0, D0, D4 and
-a 3.3V logic level serial terminal to PD5. The LEDs will flash and an incrementing
-count will be printed to the serial port at rates that are controlled by the
-Systick IRQ.

examples/systick_irq_millis/systick.h

-/*
- * Single-File-Header for using SysTick with millisecond interrupts
- * 03-25-2023 E. Brombaugh
- */
-
-#ifndef _SYSTICK_H
-#define _SYSTICK_H
-
-#include <stdint.h>
-
-/* some bit definitions for systick regs */
-#define SYSTICK_SR_CNTIF (1<<0)
-#define SYSTICK_CTLR_STE (1<<0)
-#define SYSTICK_CTLR_STIE (1<<1)
-#define SYSTICK_CTLR_STCLK (1<<2)
-#define SYSTICK_CTLR_STRE (1<<3)
-#define SYSTICK_CTLR_SWIE (1<<31)
-
-volatile uint32_t systick_cnt;
-
-/*
- * Start up the SysTick IRQ
- */
-void systick_init(void)
-{
-	/* enable the SysTick IRQ */
-	NVIC_EnableIRQ(SysTicK_IRQn);
-	
-	/* Clear any existing IRQ */
-    SysTick->SR &= ~SYSTICK_SR_CNTIF;
-	
-	/* Set the tick interval to 1ms for normal op */
-    SysTick->CMP = (SYSTEM_CORE_CLOCK/1000)-1;
-	
-	/* Start at zero */
-    SysTick->CNT = 0;
-	systick_cnt = 0;
-	
-	/* Enable SysTick counter, IRQ, HCLK/1, auto reload */
-    SysTick->CTLR = SYSTICK_CTLR_STE | SYSTICK_CTLR_STIE | 
-					SYSTICK_CTLR_STCLK | SYSTICK_CTLR_STRE;
-}
-
-#if 1
-/*
- * SysTick ISR just counts ticks
- * note - the __attribute__((interrupt)) syntax is crucial!
- */
-void SysTick_Handler(void) __attribute__((interrupt));
-void SysTick_Handler(void)
-{
-	/* clear IRQ */
-    SysTick->SR &= 0;
-	
-	/* update counter */
-	systick_cnt++;
-}
-#endif
-
-/*
- * Millisecond delay routine
- */
-void systick_delay_ms(uint32_t milliseconds)
-{
-	/* compute end time */
-	uint32_t etime = systick_cnt + milliseconds;
-	
-	/* wait for current time == end time */
-	while(systick_cnt != etime);
-}
-
-uint32_t millis() {
-    return systick_cnt;
-}
-#endif

examples/systick_irq_millis/systick_irq_millis.c

-/*
- * Example for using SysTick with IRQs
- * 03-25-2023 E. Brombaugh
- */
-
-// Could be defined here, or in the processor defines.
-#define SYSTEM_CORE_CLOCK 48000000
-#define APB_CLOCK SYSTEM_CORE_CLOCK
-
-#include "ch32v003fun.h"
-#include <stdio.h>
-#include "systick.h"
-
-int main()
-{
-	uint32_t count = 0;
-	
-	SystemInit48HSI();
-
-	// start serial @ default 115200bps
-	SetupUART( UART_BRR );
-	printf("\r\r\n\nsystick_irq example\n\r");
-
-	printf("SysTick_Handler = 0x%08X\n\r", SysTick_Handler);
-
-	// init systick @ 1ms rate
-	printf("initializing systick...");
-	systick_init();
-	printf("done.\n\r");
-	
-	// Enable GPIOs
-	RCC->APB2PCENR |= RCC_APB2Periph_GPIOD | RCC_APB2Periph_GPIOC;
-
-	// GPIO D0 Push-Pull
-	GPIOD->CFGLR &= ~(0xf<<(4*0));
-	GPIOD->CFGLR |= (GPIO_Speed_10MHz | GPIO_CNF_OUT_PP)<<(4*0);
-
-	// GPIO D4 Push-Pull
-	GPIOD->CFGLR &= ~(0xf<<(4*4));
-	GPIOD->CFGLR |= (GPIO_Speed_10MHz | GPIO_CNF_OUT_PP)<<(4*4);
-
-	// GPIO C0 Push-Pull
-	GPIOC->CFGLR &= ~(0xf<<(4*0));
-	GPIOC->CFGLR |= (GPIO_Speed_10MHz | GPIO_CNF_OUT_PP)<<(4*0);
-
-	const uint16_t led_i = 250;
-	uint32_t led_t_last;
-	uint8_t led_progstep = 0;
-
-	printf("looping...\n\r");
-	while(1)
-	{
-		if (millis() - led_t_last >= led_i) {
-			switch (led_progstep) {
-				case 0:
-					GPIOD->BSHR = 1 | (1<<4);	 // Turn on GPIOs
-					break;
-				case 1:
-					GPIOC->BSHR = 1;
-					break;
-				case 2:
-					GPIOD->BSHR = (1<<16) | (1<<(16+4)); // Turn off GPIODs
-					break;
-				case 3:
-					GPIOC->BSHR = (1<<16);
-					printf( "Count: %lu\n\r", count++ );
-					break;
-			}
-			led_progstep++;
-			led_t_last = millis();
-			if (led_progstep > 3) {
-				led_progstep = 0;
-			}
-		}
-	}
-}