uptime -- tells how long the system has been running

Makefile

@@ -30,7 +30,8 @@ PROJECT = f030f4
 #SRCS = startup.c init.c success.c
 #SRCS = startup.c board.c success.c
 #SRCS = startup.c usart1tx.c hello.c
-SRCS = startup.c uplow.1.c uptime.1.c
+#SRCS = startup.c uplow.1.c uptime.1.c
+SRCS = startup.c uplow.2.c uptime.c printf.c putchar.c
 OBJS = $(SRCS:.c=.o)
 CPU = -mthumb -mcpu=cortex-m0
 CFLAGS = $(CPU) -g -Wall -Wextra -Os

printf.c

@@ -0,0 +1,77 @@
+/* printf.c -- format and print data    */
+/* Copyright (c) 2020 Renaud Fivet      */
+
+#include <stdarg.h>
+#include <stdio.h>
+#include "system.h" /* kputc(), kputs() */
+
+static int kputu( unsigned u, unsigned d) {
+    char s[ 12] ;                   /* room for 11 octal digit + EOS */
+    char *p = &s[ sizeof s - 1] ;   /* point to last byte */
+
+    *p = 0 ;                        /* null terminated string */
+    do {
+        unsigned r = u % d ;
+        u /= d ;
+        *--p = "0123456789ABCDEF"[ r] ;
+    } while( u) ;
+
+    return kputs( p) ;
+}
+
+static int kputi( int i) {
+    int flag = i < 0 ;
+    if( flag) {
+        i = -i ;
+        kputc( '-') ;
+    }
+
+    return flag + kputu( i, 10) ;
+}
+
+int printf( const char *fmt, ...) {
+    va_list ap ;
+    int cnt = 0 ;
+    int c ; /* current char in format string */
+
+    va_start( ap, fmt) ;
+    while( ( c = *fmt++) != 0)
+        if( c != '%') {
+            cnt += 1 ; kputc( c) ;
+        } else if( ( c = *fmt++) == 0) {
+            cnt += 1 ; kputc( '%') ;
+            break ;
+        } else
+            switch( c) {
+            case 'c':
+                cnt += 1 ; kputc( va_arg( ap, int /* char */)) ;
+                break ;
+            case 'o':
+                cnt += kputu( va_arg( ap, unsigned), 8) ;
+                break ;
+            case 'u':
+                cnt += kputu( va_arg( ap, unsigned), 10) ;
+                break ;
+            case 'x':
+            case 'X':
+                cnt += kputu( va_arg( ap, unsigned), 16) ;
+                break ;
+            case 'i':
+            case 'd':
+                cnt += kputi( va_arg( ap, int)) ;
+                break ;
+            case 's':
+                cnt += kputs( va_arg( ap, char *)) ;
+                break ;
+            default:
+                cnt += 1 ; kputc( '%') ;
+                /* fallthrough */
+            case '%':
+                cnt += 1 ; kputc( c) ;
+            }
+
+    va_end( ap) ;
+    return cnt ;
+}
+
+/* end of printf.c */

putchar.c

@@ -0,0 +1,12 @@
+/* putchar.c -- write a character to stdout */
+/* Copyright (c) 2020 Renaud Fivet          */
+
+#include <stdio.h>
+#include "system.h" /* kputc() */
+
+int putchar( int c) {
+    kputc( c) ;
+    return c ;
+}
+
+/* end of putchar.c */

system.h

@@ -0,0 +1,12 @@
+/* system.h -- system services      */
+/* Copyright (c) 2020 Renaud Fivet  */
+
+extern volatile unsigned uptime ;   /* seconds elapsed since boot */
+
+int init( void) ;           /* System initialization, called once at startup */
+
+void kputc( unsigned char c) ;      /* character output */
+int  kputs( const char s[]) ;       /* string output */
+void yield( void) ;                 /* give way */
+
+/* end of system.h */

uplow.2.c

@@ -0,0 +1,124 @@
+/* uplow.2.c -- uptime lower layer
+** Copyright (c) 2020 Renaud Fivet
+**
+** implements system.h interface
+** uptime = seconds elapsed since boot
+** SysClck 8MHz HSI based, baudrate 9600, Busy wait transmission
+** user LED toggled every second
+** SysTick interrupt every second
+*/
+
+#include "system.h" /* implements system.h */
+
+#define SYSTICK                 ((volatile long *) 0xE000E010)
+#define SYSTICK_CSR             SYSTICK[ 0]
+#define SYSTICK_RVR             SYSTICK[ 1]
+#define SYSTICK_CVR             SYSTICK[ 2]
+
+#define CAT( a, b) a##b
+#define HEXA( a) CAT( 0x, a)
+#define RCC                     ((volatile long *) 0x40021000)
+#define RCC_AHBENR              RCC[ 5]
+#define RCC_AHBENR_IOP( h)      (1 << (17 + HEXA( h) - 0xA))
+#define RCC_APB2ENR             RCC[ 6]
+#define RCC_APB2ENR_USART1EN    0x00004000  /* 14: USART1 clock enable */
+
+#define GPIOA                   ((volatile long *) 0x48000000)
+#define GPIOB                   ((volatile long *) 0x48000400)
+#define GPIO( x) CAT( GPIO, x)
+#define MODER   0
+#define ODR     5
+#define AFRH    9
+
+#define USART1                  ((volatile long *) 0x40013800)
+#define CR1     0               /* Config */
+#define BRR     3               /* Baudrate */
+#define ISR     7               /* Interrupt and Status */
+#define TDR     10              /* Transmit Data */
+#define USART_CR1_TE    8           /* 3: Transmit Enable */
+#define USART_CR1_RE    4           /* 2: Receive Enable */
+#define USART_CR1_UE    1           /* 0: USART Enable */
+#define USART_ISR_TXE   (1 << 7)    /* 7: Transmit Data Register Empty */
+
+/* user LED ON when PA4 is high */
+#define LED_IOP A
+#define LED_PIN 4
+#define LED_ON  1
+
+void kputc( unsigned char c) {  /* character output */
+    static unsigned char lastc ;
+
+    if( c == '\n' && lastc != '\r')
+        kputc( '\r') ;
+
+/* Active wait while transmit register is full */
+    while( (USART1[ ISR] & USART_ISR_TXE) == 0) ;
+
+    USART1[ TDR] = c ;
+    lastc = c ;
+}
+
+int kputs( const char s[]) {    /* string output */
+    int cnt = 0 ;
+    int c ;
+
+    while( (c = *s++) != 0) {
+        kputc( c) ;
+        cnt += 1 ;
+    }
+
+    return cnt ;
+}
+
+void yield( void) {             /* give way */
+    __asm( "WFI") ; /* Wait for System Tick Interrupt */
+}
+
+volatile unsigned uptime ;      /* seconds elapsed since boot */
+
+#ifdef LED_ON
+static void userLEDtoggle( void) {
+    GPIO( LED_IOP)[ ODR] ^= 1 << LED_PIN ;   /* Toggle User LED */
+}
+#endif
+
+void SysTick_Handler( void) {
+    uptime += 1 ;
+#ifdef LED_ON
+    userLEDtoggle() ;
+#endif
+}
+
+int init( void) {
+/* By default SYSCLK == HSI [8MHZ] */
+
+/* SYSTICK */
+    SYSTICK_RVR = 1000000 - 1 ;     /* HBA / 8 */
+    SYSTICK_CVR = 0 ;
+    SYSTICK_CSR = 3 ;               /* HBA / 8, Interrupt ON, Enable */
+    /* SysTick_Handler will execute every 1s from now on */
+
+#ifdef LED_ON
+/* User LED ON */
+    RCC_AHBENR |= RCC_AHBENR_IOP( LED_IOP) ;        /* Enable IOPx periph */
+    GPIO( LED_IOP)[ MODER] |= 1 << (LED_PIN * 2) ;  /* LED_IO Output [01],
+                                                    ** over default 00 */
+    /* OTYPER Push-Pull by default */
+    /* Pxn output default LOW at reset */
+# if LED_ON
+    userLEDtoggle() ;
+# endif
+#endif
+
+/* USART1 9600 8N1 */
+    RCC_AHBENR |= RCC_AHBENR_IOP( A) ;  /* Enable GPIOA periph */
+    GPIOA[ MODER] |= 0x0A << (9 * 2) ;  /* PA9-10 ALT 10, over default 00 */
+    GPIOA[ AFRH] |= 0x110 ;             /* PA9-10 AF1 0001, over default 0000 */
+    RCC_APB2ENR |= RCC_APB2ENR_USART1EN ;
+    USART1[ BRR] = 8000000 / 9600 ;     /* PCLK [8MHz] */
+    USART1[ CR1] |= USART_CR1_UE | USART_CR1_TE ;   /* Enable USART & Tx */
+
+    return 0 ;
+}
+
+/* end of uplow.2.c */

uptime.1.c

@@ -1,4 +1,4 @@
-/* uptime.1.c --tells how long the system has been running
+/* uptime.1.c -- tells how long the system has been running
 ** Copyright (c) 2020 Renaud Fivet
 **
 ** v1 displays the number of seconds elapsed since boot

uptime.c

@@ -0,0 +1,47 @@
+/* uptime.c -- tells how long the system has been running   */
+/* Copyright (c) 2020 Renaud Fivet                          */
+
+#include <stdio.h>
+#include "system.h" /* uptime, yield() */
+
+static void display( unsigned u, const char *s) {
+    if( u)
+        printf( " %d %s%s", u, s, &"s"[ u <= 1]) ;
+}
+
+int main( void) {
+    static unsigned last ;
+
+    for( ;;)
+        if( last != uptime) {
+            unsigned w, d, h, m ,s ;
+
+            last = uptime ;
+            d = h = m = 0 ;
+            s = last % 60 ;
+            w = last / 60 ;
+            if( w) {
+                m = w % 60 ;
+                w /= 60 ;
+                if( w) {
+                    h = w % 24 ;
+                    w /= 24 ;
+                    if( w) {
+                        d = w % 7 ;
+                        w /= 7 ;
+                    }
+                }
+            }
+
+            printf( "up") ;
+            display( w, "week") ;
+            display( d, "day") ;
+            display( h, "hour") ;
+            display( m, "minute") ;
+            display( s, "second") ;
+            printf( "\n") ;
+        } else
+            yield() ;   /* Wait for System Tick Interrupt */
+}
+
+/* end of uptime.c */