interrupts and started pit

Makefile

@@ -10,14 +10,20 @@ KOBJ := $(addprefix $(BUILDDIR)/, \
 		$(patsubst %.asm,%.o, $(patsubst %.c,%.o, $(KSRC)))))
 KIMG := kernel.bin
 
+LSRC := $(wildcard lib/*.c)
+LOBJ := $(addprefix $(BUILDDIR)/, \
+		$(notdir \
+		$(patsubst %.c,%.o, $(LSRC))))
+
 ISO := Hazel.iso
 
-CFLAGS    := -ffreestanding -Wall -Wextra -Werror -I $(INCLUDEDIR)
+CFLAGS    := -ffreestanding -Wall -Wextra -Werror -I $(INCLUDEDIR) -I lib
 LDFLAGS   := -ffreestanding -nostdlib -lgcc -T kernel/kernel.ld
 QEMUFLAGS := -cdrom $(BUILDDIR)/$(ISO) \
+			 -d int \
 			 -serial stdio
 
-$(BUILDDIR)/$(KIMG): $(KOBJ)
+$(BUILDDIR)/$(KIMG): $(KOBJ) $(LOBJ)
 	$(CC) $^ -o $@ $(LDFLAGS)
 $(BUILDDIR)/%.o: */%.asm
 	$(AS) -felf32 $^ -o $@

bochsrc

@@ -0,0 +1,5 @@
+ata0-slave: type=cdrom, path=./build/Hazel.iso, status=inserted
+magic_break: enabled=1
+boot: cdrom
+
+display_library: sdl2

include/kernel/idt.h

@@ -0,0 +1,50 @@
+#ifndef HAZEL_IDT_H_
+#define HAZEL_IDT_H_
+
+#include <stdint.h>
+
+#define GDT_SEGMENT_SELECTOR(i, p) ((i << 3) | p)
+#define LDT_SEGMENT_SELECTOR(i, p) ((i << 3) | 0x04 | p)
+
+#define IDT_ENTRY_COUNT 256
+
+struct idt_entry {
+   uint16_t offset_lo; 
+   uint16_t seg_select;
+   uint8_t  reserved;
+   uint8_t  attributes;
+   uint16_t offset_hi;
+} __attribute__ ((packed));
+
+struct idtr {
+    uint16_t size;
+    uint32_t base;
+} __attribute__ ((packed));
+
+enum IDT_ATTRIBUTES {
+    TASK_GATE    = 0x05,
+    INT_GATE_16  = 0x06,
+    TRAP_GATE_16 = 0x07,
+    INT_GATE_32  = 0x0E,
+    TRAP_GATE_32 = 0x0F,
+
+    INT_RING0 = 0x00,
+    INT_RING1 = 0x20,
+    INT_RING2 = 0x40,
+    INT_RING3 = 0x60,
+
+    INT_PRESENT = 0x80,
+};
+
+typedef struct {
+    uint32_t edi, esi, ebp, esp, ebx, edx, ecx, eax; /*  Pushed by pusha. */
+    uint32_t int_no, err_code;    /*  Interrupt number and error code (if applicable) */
+
+    uint32_t eip;
+    uint32_t cs;
+    uint32_t eflags;
+} int_stack_frame_t;
+
+void idt_encode_entry(struct idt_entry idt[], int i, uint32_t offset, uint16_t segment_selector, uint8_t attributes);
+
+#endif

include/kernel/log.h

@@ -1,12 +1,14 @@
 #ifndef HAZEL_LOG_H_
 #define HAZEL_LOG_H_
 
+#include <printf.h>
+
 typedef enum {
     LOG_COM1,
     LOG_VGA,
 } log_method_t;
 
-#define LOG(x) logs(x);
+#define LOG(...) printf(__VA_ARGS__);
 
 void logs(const char *str);
 

include/kernel/pic.h

@@ -0,0 +1,30 @@
+#ifndef HAZEL_PIC_H_
+#define HAZEL_PIC_H_
+
+#define PIC_1_COMMAND 0x20
+#define PIC_2_COMMAND 0xA0
+#define PIC_1_DATA    0x21
+#define PIC_2_DATA    0xA1
+
+#define PIC_EOI 0x20
+
+#define PIC_1_START 32
+#define PIC_2_START  40
+
+#define PIC_1_ICW3 0x04
+#define PIC_2_ICW3 0x02 
+
+#include <kernel/io.h>
+
+enum ICW1 {
+    ICW4_NEEDED = 0x01,
+    SINGLE_MODE = 0x02,
+    INTERVAL_4  = 0x04,
+    LVL_TRIGGER = 0x08,
+    INIT_BIT    = 0x10,
+};
+
+void pic_send_eoi(uint8_t irq);
+void pic_remap(int pic1_start, int pic2_start);
+
+#endif

include/kernel/pit.h

@@ -0,0 +1,17 @@
+#ifndef HAZEL_PIT_H_
+#define HAZEL_PIT_H_
+
+#define PIT_CHAN0_DATA 0x40
+#define PIT_CHAN1_DATA 0x41
+#define PIT_CHAN2_DATA 0x42
+#define PIT_MODE_CMD   0x43
+
+#define PIT_MODE0  0
+#define PIT_LOBYTE (1<<4)
+#define PIT_LOHIGH (3<<4)
+#define PIT_CHAN0  0
+
+void pit_init(void);
+void pit_handler(void);
+
+#endif

kernel/idt.c

@@ -0,0 +1,9 @@
+#include <kernel/idt.h>
+
+void idt_encode_entry(struct idt_entry idt[], int i, uint32_t offset, uint16_t segment_selector, uint8_t attributes) {
+   idt[i].offset_lo = (uint16_t)(offset & 0xFFFF);
+   idt[i].seg_select = segment_selector;
+   idt[i].reserved = 0;
+   idt[i].attributes = attributes;
+   idt[i].offset_hi = (uint16_t)(offset >> 16);
+}

kernel/init.asm

@@ -51,6 +51,77 @@ halt:
     hlt
     jmp halt
 
+global pit_isr
+pit_isr:
+    cli
+    extern pit_handler
+    call pit_handler
+    iret
+
+extern exception_handler
+%macro isr_err_stub 1
+isr_stub_%+%1:
+    cli
+    push %1
+    pusha
+    call exception_handler
+    popa
+    add esp, 8
+    iret 
+%endmacro
+%macro isr_no_err_stub 1
+isr_stub_%+%1:
+    cli
+    push 0
+    push %1
+    pusha
+    call exception_handler
+    popa
+    add esp, 12
+    iret 
+%endmacro
+
+isr_no_err_stub 0
+isr_no_err_stub 1
+isr_no_err_stub 2
+isr_no_err_stub 3
+isr_no_err_stub 4
+isr_no_err_stub 5
+isr_no_err_stub 6
+isr_no_err_stub 7
+isr_err_stub    8
+isr_no_err_stub 9
+isr_err_stub    10
+isr_err_stub    11
+isr_err_stub    12
+isr_err_stub    13
+isr_err_stub    14
+isr_no_err_stub 15
+isr_no_err_stub 16
+isr_err_stub    17
+isr_no_err_stub 18
+isr_no_err_stub 19
+isr_no_err_stub 20
+isr_no_err_stub 21
+isr_no_err_stub 22
+isr_no_err_stub 23
+isr_no_err_stub 24
+isr_no_err_stub 25
+isr_no_err_stub 26
+isr_no_err_stub 27
+isr_no_err_stub 28
+isr_no_err_stub 29
+isr_err_stub    30
+isr_no_err_stub 31
+
+global isr_stub_table
+isr_stub_table:
+%assign i 0 
+%rep    32 
+    dd isr_stub_%+i
+%assign i i+1 
+%endrep
+
 section .data
 ; GDT for a flat memory layout
 ; We get access to all memory and can utilize paging

kernel/kernel.c

@@ -1,8 +1,23 @@
 #include <kernel/kernel.h>
 #include <kernel/multiboot.h>
 #include <kernel/serial.h>
+#include <kernel/idt.h>
+#include <kernel/pic.h>
+#include <kernel/pit.h>
 
 kernel_ctx_t ctx = {0};
+struct idt_entry idt[256] = {0};
+struct idtr idtr = {0};
+
+extern uint32_t isr_stub_table[32];
+extern void pit_isr(void);
+
+void exception_handler(int_stack_frame_t r) {
+    LOG("Exception 0x%X (0x%X) has occurred\nEAX: 0x%08X\nECX: 0x%08X\nEDX: 0x%08X\nEBX: 0x%08X\nESI: 0x%08X\nEDI: 0x%08X\nEBP: 0x%08X\nESP: 0x%08X\n",
+            r.int_no, r.err_code, r.eax, r.ecx, r.edx, r.ebx, r.esi, r.edi, r.ebp, r.esp+24); 
+    LOG("\nEIP:     0x%08X\nCS:      0x%08X\nEFLAGS:  0x%08X\n",
+            r.eip, r.cs, r.eflags);
+}
 
 void kernel(multiboot_info_t *info) {
     if (!CHECK_FLAG(info->flags, 6)) goto halt;  // Memory map
@@ -13,6 +28,20 @@ void kernel(multiboot_info_t *info) {
     if (serial_port_init(COM1)) ctx.log_method = LOG_COM1;
 
     LOG("Kernel log being sent to COM1\n");
+
+    for (int i = 0; i < 32; i++) {
+        idt_encode_entry(idt, i, isr_stub_table[i], GDT_SEGMENT_SELECTOR(1, 0), TRAP_GATE_32 | INT_RING0 | INT_PRESENT);
+    }
+    idt_encode_entry(idt, 32, (uint32_t)pit_isr, GDT_SEGMENT_SELECTOR(1, 0), TRAP_GATE_32 | INT_RING0 | INT_PRESENT);
+    
+    idtr.size = (sizeof(struct idt_entry) * 256) - 1;
+    idtr.base = (uint32_t) idt;
+
+    asm volatile ("lidt %0" :: "m"(idtr));
+    pic_remap(PIC_1_START, PIC_2_START);
+    asm volatile ("sti" ::);
+
+    pit_init();
 halt:
     asm volatile ("cli" ::);
     for (;;) {}

kernel/log.c

@@ -4,6 +4,16 @@
 
 extern kernel_ctx_t ctx;
 
+void _putchar(char c) {
+    switch (ctx.log_method) {
+	case LOG_COM1:
+	    serial_putc(COM1, c);
+	    break;
+	default:
+	    break;
+    }
+}
+
 void logs(const char *str) {
     switch (ctx.log_method) {
 	case LOG_COM1:

kernel/pic.c

@@ -0,0 +1,31 @@
+#include <kernel/pic.h>
+#include <kernel/io.h>
+
+void pic_send_eoi(uint8_t irq) {
+    if (irq > 7)
+        outb(PIC_2_COMMAND, PIC_EOI);
+    else
+        outb(PIC_1_COMMAND, PIC_EOI);
+}
+
+void pic_remap(int pic1_start, int pic2_start) {
+    // Mask all IRQ lines
+    outb(PIC_1_DATA, 0xff);
+    outb(PIC_2_DATA, 0xff);
+
+    // Initialize master PIC
+    outb(PIC_1_COMMAND, ICW4_NEEDED | INIT_BIT);
+    outb(PIC_1_DATA, pic1_start);
+    outb(PIC_1_DATA, PIC_1_ICW3);
+    outb(PIC_1_DATA, 0x01);
+
+    // Initialize slave PIC
+    outb(PIC_2_COMMAND, ICW4_NEEDED | INIT_BIT);
+    outb(PIC_2_DATA, pic2_start);
+    outb(PIC_2_DATA, PIC_2_ICW3);
+    outb(PIC_2_DATA, 0x01);
+
+    // Unmask
+    //outb(PIC_1_DATA, 0b11111101);
+    //outb(PIC_2_DATA, 0b11111101);
+}

kernel/pit.c

@@ -0,0 +1,14 @@
+#include <kernel/pit.h>
+#include <kernel/io.h>
+#include <kernel/pic.h>
+
+void pit_init(void) {
+    outb(PIT_MODE_CMD, PIT_CHAN0 | PIT_LOHIGH | PIT_MODE0);
+
+    outb(PIT_CHAN0, 1);
+    outb(PIT_CHAN0, 0);
+}
+
+void pit_handler(void) {
+    pic_send_eoi(0);
+}

lib/printf.c

@@ -0,0 +1,914 @@
+///////////////////////////////////////////////////////////////////////////////
+// \author (c) Marco Paland (info@paland.com)
+//             2014-2019, PALANDesign Hannover, Germany
+//
+// \license The MIT License (MIT)
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+//
+// \brief Tiny printf, sprintf and (v)snprintf implementation, optimized for speed on
+//        embedded systems with a very limited resources. These routines are thread
+//        safe and reentrant!
+//        Use this instead of the bloated standard/newlib printf cause these use
+//        malloc for printf (and may not be thread safe).
+//
+///////////////////////////////////////////////////////////////////////////////
+
+#include <stdbool.h>
+#include <stdint.h>
+
+#include "printf.h"
+
+
+// define this globally (e.g. gcc -DPRINTF_INCLUDE_CONFIG_H ...) to include the
+// printf_config.h header file
+// default: undefined
+#ifdef PRINTF_INCLUDE_CONFIG_H
+#include "printf_config.h"
+#endif
+
+
+// 'ntoa' conversion buffer size, this must be big enough to hold one converted
+// numeric number including padded zeros (dynamically created on stack)
+// default: 32 byte
+#ifndef PRINTF_NTOA_BUFFER_SIZE
+#define PRINTF_NTOA_BUFFER_SIZE    32U
+#endif
+
+// 'ftoa' conversion buffer size, this must be big enough to hold one converted
+// float number including padded zeros (dynamically created on stack)
+// default: 32 byte
+#ifndef PRINTF_FTOA_BUFFER_SIZE
+#define PRINTF_FTOA_BUFFER_SIZE    32U
+#endif
+
+// support for the floating point type (%f)
+// default: activated
+#ifndef PRINTF_DISABLE_SUPPORT_FLOAT
+#define PRINTF_SUPPORT_FLOAT
+#endif
+
+// support for exponential floating point notation (%e/%g)
+// default: activated
+#ifndef PRINTF_DISABLE_SUPPORT_EXPONENTIAL
+#define PRINTF_SUPPORT_EXPONENTIAL
+#endif
+
+// define the default floating point precision
+// default: 6 digits
+#ifndef PRINTF_DEFAULT_FLOAT_PRECISION
+#define PRINTF_DEFAULT_FLOAT_PRECISION  6U
+#endif
+
+// define the largest float suitable to print with %f
+// default: 1e9
+#ifndef PRINTF_MAX_FLOAT
+#define PRINTF_MAX_FLOAT  1e9
+#endif
+
+// support for the long long types (%llu or %p)
+// default: activated
+#ifndef PRINTF_DISABLE_SUPPORT_LONG_LONG
+#define PRINTF_SUPPORT_LONG_LONG
+#endif
+
+// support for the ptrdiff_t type (%t)
+// ptrdiff_t is normally defined in <stddef.h> as long or long long type
+// default: activated
+#ifndef PRINTF_DISABLE_SUPPORT_PTRDIFF_T
+#define PRINTF_SUPPORT_PTRDIFF_T
+#endif
+
+///////////////////////////////////////////////////////////////////////////////
+
+// internal flag definitions
+#define FLAGS_ZEROPAD   (1U <<  0U)
+#define FLAGS_LEFT      (1U <<  1U)
+#define FLAGS_PLUS      (1U <<  2U)
+#define FLAGS_SPACE     (1U <<  3U)
+#define FLAGS_HASH      (1U <<  4U)
+#define FLAGS_UPPERCASE (1U <<  5U)
+#define FLAGS_CHAR      (1U <<  6U)
+#define FLAGS_SHORT     (1U <<  7U)
+#define FLAGS_LONG      (1U <<  8U)
+#define FLAGS_LONG_LONG (1U <<  9U)
+#define FLAGS_PRECISION (1U << 10U)
+#define FLAGS_ADAPT_EXP (1U << 11U)
+
+
+// import float.h for DBL_MAX
+#if defined(PRINTF_SUPPORT_FLOAT)
+#include <float.h>
+#endif
+
+
+// output function type
+typedef void (*out_fct_type)(char character, void* buffer, size_t idx, size_t maxlen);
+
+
+// wrapper (used as buffer) for output function type
+typedef struct {
+  void  (*fct)(char character, void* arg);
+  void* arg;
+} out_fct_wrap_type;
+
+
+// internal buffer output
+static inline void _out_buffer(char character, void* buffer, size_t idx, size_t maxlen)
+{
+  if (idx < maxlen) {
+    ((char*)buffer)[idx] = character;
+  }
+}
+
+
+// internal null output
+static inline void _out_null(char character, void* buffer, size_t idx, size_t maxlen)
+{
+  (void)character; (void)buffer; (void)idx; (void)maxlen;
+}
+
+
+// internal _putchar wrapper
+static inline void _out_char(char character, void* buffer, size_t idx, size_t maxlen)
+{
+  (void)buffer; (void)idx; (void)maxlen;
+  if (character) {
+    _putchar(character);
+  }
+}
+
+
+// internal output function wrapper
+static inline void _out_fct(char character, void* buffer, size_t idx, size_t maxlen)
+{
+  (void)idx; (void)maxlen;
+  if (character) {
+    // buffer is the output fct pointer
+    ((out_fct_wrap_type*)buffer)->fct(character, ((out_fct_wrap_type*)buffer)->arg);
+  }
+}
+
+
+// internal secure strlen
+// \return The length of the string (excluding the terminating 0) limited by 'maxsize'
+static inline unsigned int _strnlen_s(const char* str, size_t maxsize)
+{
+  const char* s;
+  for (s = str; *s && maxsize--; ++s);
+  return (unsigned int)(s - str);
+}
+
+
+// internal test if char is a digit (0-9)
+// \return true if char is a digit
+static inline bool _is_digit(char ch)
+{
+  return (ch >= '0') && (ch <= '9');
+}
+
+
+// internal ASCII string to unsigned int conversion
+static unsigned int _atoi(const char** str)
+{
+  unsigned int i = 0U;
+  while (_is_digit(**str)) {
+    i = i * 10U + (unsigned int)(*((*str)++) - '0');
+  }
+  return i;
+}
+
+
+// output the specified string in reverse, taking care of any zero-padding
+static size_t _out_rev(out_fct_type out, char* buffer, size_t idx, size_t maxlen, const char* buf, size_t len, unsigned int width, unsigned int flags)
+{
+  const size_t start_idx = idx;
+
+  // pad spaces up to given width
+  if (!(flags & FLAGS_LEFT) && !(flags & FLAGS_ZEROPAD)) {
+    for (size_t i = len; i < width; i++) {
+      out(' ', buffer, idx++, maxlen);
+    }
+  }
+
+  // reverse string
+  while (len) {
+    out(buf[--len], buffer, idx++, maxlen);
+  }
+
+  // append pad spaces up to given width
+  if (flags & FLAGS_LEFT) {
+    while (idx - start_idx < width) {
+      out(' ', buffer, idx++, maxlen);
+    }
+  }
+
+  return idx;
+}
+
+
+// internal itoa format
+static size_t _ntoa_format(out_fct_type out, char* buffer, size_t idx, size_t maxlen, char* buf, size_t len, bool negative, unsigned int base, unsigned int prec, unsigned int width, unsigned int flags)
+{
+  // pad leading zeros
+  if (!(flags & FLAGS_LEFT)) {
+    if (width && (flags & FLAGS_ZEROPAD) && (negative || (flags & (FLAGS_PLUS | FLAGS_SPACE)))) {
+      width--;
+    }
+    while ((len < prec) && (len < PRINTF_NTOA_BUFFER_SIZE)) {
+      buf[len++] = '0';
+    }
+    while ((flags & FLAGS_ZEROPAD) && (len < width) && (len < PRINTF_NTOA_BUFFER_SIZE)) {
+      buf[len++] = '0';
+    }
+  }
+
+  // handle hash
+  if (flags & FLAGS_HASH) {
+    if (!(flags & FLAGS_PRECISION) && len && ((len == prec) || (len == width))) {
+      len--;
+      if (len && (base == 16U)) {
+        len--;
+      }
+    }
+    if ((base == 16U) && !(flags & FLAGS_UPPERCASE) && (len < PRINTF_NTOA_BUFFER_SIZE)) {
+      buf[len++] = 'x';
+    }
+    else if ((base == 16U) && (flags & FLAGS_UPPERCASE) && (len < PRINTF_NTOA_BUFFER_SIZE)) {
+      buf[len++] = 'X';
+    }
+    else if ((base == 2U) && (len < PRINTF_NTOA_BUFFER_SIZE)) {
+      buf[len++] = 'b';
+    }
+    if (len < PRINTF_NTOA_BUFFER_SIZE) {
+      buf[len++] = '0';
+    }
+  }
+
+  if (len < PRINTF_NTOA_BUFFER_SIZE) {
+    if (negative) {
+      buf[len++] = '-';
+    }
+    else if (flags & FLAGS_PLUS) {
+      buf[len++] = '+';  // ignore the space if the '+' exists
+    }
+    else if (flags & FLAGS_SPACE) {
+      buf[len++] = ' ';
+    }
+  }
+
+  return _out_rev(out, buffer, idx, maxlen, buf, len, width, flags);
+}
+
+
+// internal itoa for 'long' type
+static size_t _ntoa_long(out_fct_type out, char* buffer, size_t idx, size_t maxlen, unsigned long value, bool negative, unsigned long base, unsigned int prec, unsigned int width, unsigned int flags)
+{
+  char buf[PRINTF_NTOA_BUFFER_SIZE];
+  size_t len = 0U;
+
+  // no hash for 0 values
+  if (!value) {
+    flags &= ~FLAGS_HASH;
+  }
+
+  // write if precision != 0 and value is != 0
+  if (!(flags & FLAGS_PRECISION) || value) {
+    do {
+      const char digit = (char)(value % base);
+      buf[len++] = digit < 10 ? '0' + digit : (flags & FLAGS_UPPERCASE ? 'A' : 'a') + digit - 10;
+      value /= base;
+    } while (value && (len < PRINTF_NTOA_BUFFER_SIZE));
+  }
+
+  return _ntoa_format(out, buffer, idx, maxlen, buf, len, negative, (unsigned int)base, prec, width, flags);
+}
+
+
+// internal itoa for 'long long' type
+#if defined(PRINTF_SUPPORT_LONG_LONG)
+static size_t _ntoa_long_long(out_fct_type out, char* buffer, size_t idx, size_t maxlen, unsigned long long value, bool negative, unsigned long long base, unsigned int prec, unsigned int width, unsigned int flags)
+{
+  char buf[PRINTF_NTOA_BUFFER_SIZE];
+  size_t len = 0U;
+
+  // no hash for 0 values
+  if (!value) {
+    flags &= ~FLAGS_HASH;
+  }
+
+  // write if precision != 0 and value is != 0
+  if (!(flags & FLAGS_PRECISION) || value) {
+    do {
+      const char digit = (char)(value % base);
+      buf[len++] = digit < 10 ? '0' + digit : (flags & FLAGS_UPPERCASE ? 'A' : 'a') + digit - 10;
+      value /= base;
+    } while (value && (len < PRINTF_NTOA_BUFFER_SIZE));
+  }
+
+  return _ntoa_format(out, buffer, idx, maxlen, buf, len, negative, (unsigned int)base, prec, width, flags);
+}
+#endif  // PRINTF_SUPPORT_LONG_LONG
+
+
+#if defined(PRINTF_SUPPORT_FLOAT)
+
+#if defined(PRINTF_SUPPORT_EXPONENTIAL)
+// forward declaration so that _ftoa can switch to exp notation for values > PRINTF_MAX_FLOAT
+static size_t _etoa(out_fct_type out, char* buffer, size_t idx, size_t maxlen, double value, unsigned int prec, unsigned int width, unsigned int flags);
+#endif
+
+
+// internal ftoa for fixed decimal floating point
+static size_t _ftoa(out_fct_type out, char* buffer, size_t idx, size_t maxlen, double value, unsigned int prec, unsigned int width, unsigned int flags)
+{
+  char buf[PRINTF_FTOA_BUFFER_SIZE];
+  size_t len  = 0U;
+  double diff = 0.0;
+
+  // powers of 10
+  static const double pow10[] = { 1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000 };
+
+  // test for special values
+  if (value != value)
+    return _out_rev(out, buffer, idx, maxlen, "nan", 3, width, flags);
+  if (value < -DBL_MAX)
+    return _out_rev(out, buffer, idx, maxlen, "fni-", 4, width, flags);
+  if (value > DBL_MAX)
+    return _out_rev(out, buffer, idx, maxlen, (flags & FLAGS_PLUS) ? "fni+" : "fni", (flags & FLAGS_PLUS) ? 4U : 3U, width, flags);
+
+  // test for very large values
+  // standard printf behavior is to print EVERY whole number digit -- which could be 100s of characters overflowing your buffers == bad
+  if ((value > PRINTF_MAX_FLOAT) || (value < -PRINTF_MAX_FLOAT)) {
+#if defined(PRINTF_SUPPORT_EXPONENTIAL)
+    return _etoa(out, buffer, idx, maxlen, value, prec, width, flags);
+#else
+    return 0U;
+#endif
+  }
+
+  // test for negative
+  bool negative = false;
+  if (value < 0) {
+    negative = true;
+    value = 0 - value;
+  }
+
+  // set default precision, if not set explicitly
+  if (!(flags & FLAGS_PRECISION)) {
+    prec = PRINTF_DEFAULT_FLOAT_PRECISION;
+  }
+  // limit precision to 9, cause a prec >= 10 can lead to overflow errors
+  while ((len < PRINTF_FTOA_BUFFER_SIZE) && (prec > 9U)) {
+    buf[len++] = '0';
+    prec--;
+  }
+
+  int whole = (int)value;
+  double tmp = (value - whole) * pow10[prec];
+  unsigned long frac = (unsigned long)tmp;
+  diff = tmp - frac;
+
+  if (diff > 0.5) {
+    ++frac;
+    // handle rollover, e.g. case 0.99 with prec 1 is 1.0
+    if (frac >= pow10[prec]) {
+      frac = 0;
+      ++whole;
+    }
+  }
+  else if (diff < 0.5) {
+  }
+  else if ((frac == 0U) || (frac & 1U)) {
+    // if halfway, round up if odd OR if last digit is 0
+    ++frac;
+  }
+
+  if (prec == 0U) {
+    diff = value - (double)whole;
+    if ((!(diff < 0.5) || (diff > 0.5)) && (whole & 1)) {
+      // exactly 0.5 and ODD, then round up
+      // 1.5 -> 2, but 2.5 -> 2
+      ++whole;
+    }
+  }
+  else {
+    unsigned int count = prec;
+    // now do fractional part, as an unsigned number
+    while (len < PRINTF_FTOA_BUFFER_SIZE) {
+      --count;
+      buf[len++] = (char)(48U + (frac % 10U));
+      if (!(frac /= 10U)) {
+        break;
+      }
+    }
+    // add extra 0s
+    while ((len < PRINTF_FTOA_BUFFER_SIZE) && (count-- > 0U)) {
+      buf[len++] = '0';
+    }
+    if (len < PRINTF_FTOA_BUFFER_SIZE) {
+      // add decimal
+      buf[len++] = '.';
+    }
+  }
+
+  // do whole part, number is reversed
+  while (len < PRINTF_FTOA_BUFFER_SIZE) {
+    buf[len++] = (char)(48 + (whole % 10));
+    if (!(whole /= 10)) {
+      break;
+    }
+  }
+
+  // pad leading zeros
+  if (!(flags & FLAGS_LEFT) && (flags & FLAGS_ZEROPAD)) {
+    if (width && (negative || (flags & (FLAGS_PLUS | FLAGS_SPACE)))) {
+      width--;
+    }
+    while ((len < width) && (len < PRINTF_FTOA_BUFFER_SIZE)) {
+      buf[len++] = '0';
+    }
+  }
+
+  if (len < PRINTF_FTOA_BUFFER_SIZE) {
+    if (negative) {
+      buf[len++] = '-';
+    }
+    else if (flags & FLAGS_PLUS) {
+      buf[len++] = '+';  // ignore the space if the '+' exists
+    }
+    else if (flags & FLAGS_SPACE) {
+      buf[len++] = ' ';
+    }
+  }
+
+  return _out_rev(out, buffer, idx, maxlen, buf, len, width, flags);
+}
+
+
+#if defined(PRINTF_SUPPORT_EXPONENTIAL)
+// internal ftoa variant for exponential floating-point type, contributed by Martijn Jasperse <m.jasperse@gmail.com>
+static size_t _etoa(out_fct_type out, char* buffer, size_t idx, size_t maxlen, double value, unsigned int prec, unsigned int width, unsigned int flags)
+{
+  // check for NaN and special values
+  if ((value != value) || (value > DBL_MAX) || (value < -DBL_MAX)) {
+    return _ftoa(out, buffer, idx, maxlen, value, prec, width, flags);
+  }
+
+  // determine the sign
+  const bool negative = value < 0;
+  if (negative) {
+    value = -value;
+  }
+
+  // default precision
+  if (!(flags & FLAGS_PRECISION)) {
+    prec = PRINTF_DEFAULT_FLOAT_PRECISION;
+  }
+
+  // determine the decimal exponent
+  // based on the algorithm by David Gay (https://www.ampl.com/netlib/fp/dtoa.c)
+  union {
+    uint64_t U;
+    double   F;
+  } conv;
+
+  conv.F = value;
+  int exp2 = (int)((conv.U >> 52U) & 0x07FFU) - 1023;           // effectively log2
+  conv.U = (conv.U & ((1ULL << 52U) - 1U)) | (1023ULL << 52U);  // drop the exponent so conv.F is now in [1,2)
+  // now approximate log10 from the log2 integer part and an expansion of ln around 1.5
+  int expval = (int)(0.1760912590558 + exp2 * 0.301029995663981 + (conv.F - 1.5) * 0.289529654602168);
+  // now we want to compute 10^expval but we want to be sure it won't overflow
+  exp2 = (int)(expval * 3.321928094887362 + 0.5);
+  const double z  = expval * 2.302585092994046 - exp2 * 0.6931471805599453;
+  const double z2 = z * z;
+  conv.U = (uint64_t)(exp2 + 1023) << 52U;
+  // compute exp(z) using continued fractions, see https://en.wikipedia.org/wiki/Exponential_function#Continued_fractions_for_ex
+  conv.F *= 1 + 2 * z / (2 - z + (z2 / (6 + (z2 / (10 + z2 / 14)))));
+  // correct for rounding errors
+  if (value < conv.F) {
+    expval--;
+    conv.F /= 10;
+  }
+
+  // the exponent format is "%+03d" and largest value is "307", so set aside 4-5 characters
+  unsigned int minwidth = ((expval < 100) && (expval > -100)) ? 4U : 5U;
+
+  // in "%g" mode, "prec" is the number of *significant figures* not decimals
+  if (flags & FLAGS_ADAPT_EXP) {
+    // do we want to fall-back to "%f" mode?
+    if ((value >= 1e-4) && (value < 1e6)) {
+      if ((int)prec > expval) {
+        prec = (unsigned)((int)prec - expval - 1);
+      }
+      else {
+        prec = 0;
+      }
+      flags |= FLAGS_PRECISION;   // make sure _ftoa respects precision
+      // no characters in exponent
+      minwidth = 0U;
+      expval   = 0;
+    }
+    else {
+      // we use one sigfig for the whole part
+      if ((prec > 0) && (flags & FLAGS_PRECISION)) {
+        --prec;
+      }
+    }
+  }
+
+  // will everything fit?
+  unsigned int fwidth = width;
+  if (width > minwidth) {
+    // we didn't fall-back so subtract the characters required for the exponent
+    fwidth -= minwidth;
+  } else {
+    // not enough characters, so go back to default sizing
+    fwidth = 0U;
+  }
+  if ((flags & FLAGS_LEFT) && minwidth) {
+    // if we're padding on the right, DON'T pad the floating part
+    fwidth = 0U;
+  }
+
+  // rescale the float value
+  if (expval) {
+    value /= conv.F;
+  }
+
+  // output the floating part
+  const size_t start_idx = idx;
+  idx = _ftoa(out, buffer, idx, maxlen, negative ? -value : value, prec, fwidth, flags & ~FLAGS_ADAPT_EXP);
+
+  // output the exponent part
+  if (minwidth) {
+    // output the exponential symbol
+    out((flags & FLAGS_UPPERCASE) ? 'E' : 'e', buffer, idx++, maxlen);
+    // output the exponent value
+    idx = _ntoa_long(out, buffer, idx, maxlen, (expval < 0) ? -expval : expval, expval < 0, 10, 0, minwidth-1, FLAGS_ZEROPAD | FLAGS_PLUS);
+    // might need to right-pad spaces
+    if (flags & FLAGS_LEFT) {
+      while (idx - start_idx < width) out(' ', buffer, idx++, maxlen);
+    }
+  }
+  return idx;
+}
+#endif  // PRINTF_SUPPORT_EXPONENTIAL
+#endif  // PRINTF_SUPPORT_FLOAT
+
+
+// internal vsnprintf
+static int _vsnprintf(out_fct_type out, char* buffer, const size_t maxlen, const char* format, va_list va)
+{
+  unsigned int flags, width, precision, n;
+  size_t idx = 0U;
+
+  if (!buffer) {
+    // use null output function
+    out = _out_null;
+  }
+
+  while (*format)
+  {
+    // format specifier?  %[flags][width][.precision][length]
+    if (*format != '%') {
+      // no
+      out(*format, buffer, idx++, maxlen);
+      format++;
+      continue;
+    }
+    else {
+      // yes, evaluate it
+      format++;
+    }
+
+    // evaluate flags
+    flags = 0U;
+    do {
+      switch (*format) {
+        case '0': flags |= FLAGS_ZEROPAD; format++; n = 1U; break;
+        case '-': flags |= FLAGS_LEFT;    format++; n = 1U; break;
+        case '+': flags |= FLAGS_PLUS;    format++; n = 1U; break;
+        case ' ': flags |= FLAGS_SPACE;   format++; n = 1U; break;
+        case '#': flags |= FLAGS_HASH;    format++; n = 1U; break;
+        default :                                   n = 0U; break;
+      }
+    } while (n);
+
+    // evaluate width field
+    width = 0U;
+    if (_is_digit(*format)) {
+      width = _atoi(&format);
+    }
+    else if (*format == '*') {
+      const int w = va_arg(va, int);
+      if (w < 0) {
+        flags |= FLAGS_LEFT;    // reverse padding
+        width = (unsigned int)-w;
+      }
+      else {
+        width = (unsigned int)w;
+      }
+      format++;
+    }
+
+    // evaluate precision field
+    precision = 0U;
+    if (*format == '.') {
+      flags |= FLAGS_PRECISION;
+      format++;
+      if (_is_digit(*format)) {
+        precision = _atoi(&format);
+      }
+      else if (*format == '*') {
+        const int prec = (int)va_arg(va, int);
+        precision = prec > 0 ? (unsigned int)prec : 0U;
+        format++;
+      }
+    }
+
+    // evaluate length field
+    switch (*format) {
+      case 'l' :
+        flags |= FLAGS_LONG;
+        format++;
+        if (*format == 'l') {
+          flags |= FLAGS_LONG_LONG;
+          format++;
+        }
+        break;
+      case 'h' :
+        flags |= FLAGS_SHORT;
+        format++;
+        if (*format == 'h') {
+          flags |= FLAGS_CHAR;
+          format++;
+        }
+        break;
+#if defined(PRINTF_SUPPORT_PTRDIFF_T)
+      case 't' :
+        flags |= (sizeof(ptrdiff_t) == sizeof(long) ? FLAGS_LONG : FLAGS_LONG_LONG);
+        format++;
+        break;
+#endif
+      case 'j' :
+        flags |= (sizeof(intmax_t) == sizeof(long) ? FLAGS_LONG : FLAGS_LONG_LONG);
+        format++;
+        break;
+      case 'z' :
+        flags |= (sizeof(size_t) == sizeof(long) ? FLAGS_LONG : FLAGS_LONG_LONG);
+        format++;
+        break;
+      default :
+        break;
+    }
+
+    // evaluate specifier
+    switch (*format) {
+      case 'd' :
+      case 'i' :
+      case 'u' :
+      case 'x' :
+      case 'X' :
+      case 'o' :
+      case 'b' : {
+        // set the base
+        unsigned int base;
+        if (*format == 'x' || *format == 'X') {
+          base = 16U;
+        }
+        else if (*format == 'o') {
+          base =  8U;
+        }
+        else if (*format == 'b') {
+          base =  2U;
+        }
+        else {
+          base = 10U;
+          flags &= ~FLAGS_HASH;   // no hash for dec format
+        }
+        // uppercase
+        if (*format == 'X') {
+          flags |= FLAGS_UPPERCASE;
+        }
+
+        // no plus or space flag for u, x, X, o, b
+        if ((*format != 'i') && (*format != 'd')) {
+          flags &= ~(FLAGS_PLUS | FLAGS_SPACE);
+        }
+
+        // ignore '0' flag when precision is given
+        if (flags & FLAGS_PRECISION) {
+          flags &= ~FLAGS_ZEROPAD;
+        }
+
+        // convert the integer
+        if ((*format == 'i') || (*format == 'd')) {
+          // signed
+          if (flags & FLAGS_LONG_LONG) {
+#if defined(PRINTF_SUPPORT_LONG_LONG)
+            const long long value = va_arg(va, long long);
+            idx = _ntoa_long_long(out, buffer, idx, maxlen, (unsigned long long)(value > 0 ? value : 0 - value), value < 0, base, precision, width, flags);
+#endif
+          }
+          else if (flags & FLAGS_LONG) {
+            const long value = va_arg(va, long);
+            idx = _ntoa_long(out, buffer, idx, maxlen, (unsigned long)(value > 0 ? value : 0 - value), value < 0, base, precision, width, flags);
+          }
+          else {
+            const int value = (flags & FLAGS_CHAR) ? (char)va_arg(va, int) : (flags & FLAGS_SHORT) ? (short int)va_arg(va, int) : va_arg(va, int);
+            idx = _ntoa_long(out, buffer, idx, maxlen, (unsigned int)(value > 0 ? value : 0 - value), value < 0, base, precision, width, flags);
+          }
+        }
+        else {
+          // unsigned
+          if (flags & FLAGS_LONG_LONG) {
+#if defined(PRINTF_SUPPORT_LONG_LONG)
+            idx = _ntoa_long_long(out, buffer, idx, maxlen, va_arg(va, unsigned long long), false, base, precision, width, flags);
+#endif
+          }
+          else if (flags & FLAGS_LONG) {
+            idx = _ntoa_long(out, buffer, idx, maxlen, va_arg(va, unsigned long), false, base, precision, width, flags);
+          }
+          else {
+            const unsigned int value = (flags & FLAGS_CHAR) ? (unsigned char)va_arg(va, unsigned int) : (flags & FLAGS_SHORT) ? (unsigned short int)va_arg(va, unsigned int) : va_arg(va, unsigned int);
+            idx = _ntoa_long(out, buffer, idx, maxlen, value, false, base, precision, width, flags);
+          }
+        }
+        format++;
+        break;
+      }
+#if defined(PRINTF_SUPPORT_FLOAT)
+      case 'f' :
+      case 'F' :
+        if (*format == 'F') flags |= FLAGS_UPPERCASE;
+        idx = _ftoa(out, buffer, idx, maxlen, va_arg(va, double), precision, width, flags);
+        format++;
+        break;
+#if defined(PRINTF_SUPPORT_EXPONENTIAL)
+      case 'e':
+      case 'E':
+      case 'g':
+      case 'G':
+        if ((*format == 'g')||(*format == 'G')) flags |= FLAGS_ADAPT_EXP;
+        if ((*format == 'E')||(*format == 'G')) flags |= FLAGS_UPPERCASE;
+        idx = _etoa(out, buffer, idx, maxlen, va_arg(va, double), precision, width, flags);
+        format++;
+        break;
+#endif  // PRINTF_SUPPORT_EXPONENTIAL
+#endif  // PRINTF_SUPPORT_FLOAT
+      case 'c' : {
+        unsigned int l = 1U;
+        // pre padding
+        if (!(flags & FLAGS_LEFT)) {
+          while (l++ < width) {
+            out(' ', buffer, idx++, maxlen);
+          }
+        }
+        // char output
+        out((char)va_arg(va, int), buffer, idx++, maxlen);
+        // post padding
+        if (flags & FLAGS_LEFT) {
+          while (l++ < width) {
+            out(' ', buffer, idx++, maxlen);
+          }
+        }
+        format++;
+        break;
+      }
+
+      case 's' : {
+        const char* p = va_arg(va, char*);
+        unsigned int l = _strnlen_s(p, precision ? precision : (size_t)-1);
+        // pre padding
+        if (flags & FLAGS_PRECISION) {
+          l = (l < precision ? l : precision);
+        }
+        if (!(flags & FLAGS_LEFT)) {
+          while (l++ < width) {
+            out(' ', buffer, idx++, maxlen);
+          }
+        }
+        // string output
+        while ((*p != 0) && (!(flags & FLAGS_PRECISION) || precision--)) {
+          out(*(p++), buffer, idx++, maxlen);
+        }
+        // post padding
+        if (flags & FLAGS_LEFT) {
+          while (l++ < width) {
+            out(' ', buffer, idx++, maxlen);
+          }
+        }
+        format++;
+        break;
+      }
+
+      case 'p' : {
+        width = sizeof(void*) * 2U;
+        flags |= FLAGS_ZEROPAD | FLAGS_UPPERCASE;
+#if defined(PRINTF_SUPPORT_LONG_LONG)
+        const bool is_ll = sizeof(uintptr_t) == sizeof(long long);
+        if (is_ll) {
+          idx = _ntoa_long_long(out, buffer, idx, maxlen, (uintptr_t)va_arg(va, void*), false, 16U, precision, width, flags);
+        }
+        else {
+#endif
+          idx = _ntoa_long(out, buffer, idx, maxlen, (unsigned long)((uintptr_t)va_arg(va, void*)), false, 16U, precision, width, flags);
+#if defined(PRINTF_SUPPORT_LONG_LONG)
+        }
+#endif
+        format++;
+        break;
+      }
+
+      case '%' :
+        out('%', buffer, idx++, maxlen);
+        format++;
+        break;
+
+      default :
+        out(*format, buffer, idx++, maxlen);
+        format++;
+        break;
+    }
+  }
+
+  // termination
+  out((char)0, buffer, idx < maxlen ? idx : maxlen - 1U, maxlen);
+
+  // return written chars without terminating \0
+  return (int)idx;
+}
+
+
+///////////////////////////////////////////////////////////////////////////////
+
+int printf_(const char* format, ...)
+{
+  va_list va;
+  va_start(va, format);
+  char buffer[1];
+  const int ret = _vsnprintf(_out_char, buffer, (size_t)-1, format, va);
+  va_end(va);
+  return ret;
+}
+
+
+int sprintf_(char* buffer, const char* format, ...)
+{
+  va_list va;
+  va_start(va, format);
+  const int ret = _vsnprintf(_out_buffer, buffer, (size_t)-1, format, va);
+  va_end(va);
+  return ret;
+}
+
+
+int snprintf_(char* buffer, size_t count, const char* format, ...)
+{
+  va_list va;
+  va_start(va, format);
+  const int ret = _vsnprintf(_out_buffer, buffer, count, format, va);
+  va_end(va);
+  return ret;
+}
+
+
+int vprintf_(const char* format, va_list va)
+{
+  char buffer[1];
+  return _vsnprintf(_out_char, buffer, (size_t)-1, format, va);
+}
+
+
+int vsnprintf_(char* buffer, size_t count, const char* format, va_list va)
+{
+  return _vsnprintf(_out_buffer, buffer, count, format, va);
+}
+
+
+int fctprintf(void (*out)(char character, void* arg), void* arg, const char* format, ...)
+{
+  va_list va;
+  va_start(va, format);
+  const out_fct_wrap_type out_fct_wrap = { out, arg };
+  const int ret = _vsnprintf(_out_fct, (char*)(uintptr_t)&out_fct_wrap, (size_t)-1, format, va);
+  va_end(va);
+  return ret;
+}

lib/printf.h

@@ -0,0 +1,117 @@
+///////////////////////////////////////////////////////////////////////////////
+// \author (c) Marco Paland (info@paland.com)
+//             2014-2019, PALANDesign Hannover, Germany
+//
+// \license The MIT License (MIT)
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+// 
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+// 
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+//
+// \brief Tiny printf, sprintf and snprintf implementation, optimized for speed on
+//        embedded systems with a very limited resources.
+//        Use this instead of bloated standard/newlib printf.
+//        These routines are thread safe and reentrant.
+//
+///////////////////////////////////////////////////////////////////////////////
+
+#ifndef _PRINTF_H_
+#define _PRINTF_H_
+
+#include <stdarg.h>
+#include <stddef.h>
+
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+
+/**
+ * Output a character to a custom device like UART, used by the printf() function
+ * This function is declared here only. You have to write your custom implementation somewhere
+ * \param character Character to output
+ */
+void _putchar(char character);
+
+
+/**
+ * Tiny printf implementation
+ * You have to implement _putchar if you use printf()
+ * To avoid conflicts with the regular printf() API it is overridden by macro defines
+ * and internal underscore-appended functions like printf_() are used
+ * \param format A string that specifies the format of the output
+ * \return The number of characters that are written into the array, not counting the terminating null character
+ */
+#define printf printf_
+int printf_(const char* format, ...);
+
+
+/**
+ * Tiny sprintf implementation
+ * Due to security reasons (buffer overflow) YOU SHOULD CONSIDER USING (V)SNPRINTF INSTEAD!
+ * \param buffer A pointer to the buffer where to store the formatted string. MUST be big enough to store the output!
+ * \param format A string that specifies the format of the output
+ * \return The number of characters that are WRITTEN into the buffer, not counting the terminating null character
+ */
+#define sprintf sprintf_
+int sprintf_(char* buffer, const char* format, ...);
+
+
+/**
+ * Tiny snprintf/vsnprintf implementation
+ * \param buffer A pointer to the buffer where to store the formatted string
+ * \param count The maximum number of characters to store in the buffer, including a terminating null character
+ * \param format A string that specifies the format of the output
+ * \param va A value identifying a variable arguments list
+ * \return The number of characters that COULD have been written into the buffer, not counting the terminating
+ *         null character. A value equal or larger than count indicates truncation. Only when the returned value
+ *         is non-negative and less than count, the string has been completely written.
+ */
+#define snprintf  snprintf_
+#define vsnprintf vsnprintf_
+int  snprintf_(char* buffer, size_t count, const char* format, ...);
+int vsnprintf_(char* buffer, size_t count, const char* format, va_list va);
+
+
+/**
+ * Tiny vprintf implementation
+ * \param format A string that specifies the format of the output
+ * \param va A value identifying a variable arguments list
+ * \return The number of characters that are WRITTEN into the buffer, not counting the terminating null character
+ */
+#define vprintf vprintf_
+int vprintf_(const char* format, va_list va);
+
+
+/**
+ * printf with output function
+ * You may use this as dynamic alternative to printf() with its fixed _putchar() output
+ * \param out An output function which takes one character and an argument pointer
+ * \param arg An argument pointer for user data passed to output function
+ * \param format A string that specifies the format of the output
+ * \return The number of characters that are sent to the output function, not counting the terminating null character
+ */
+int fctprintf(void (*out)(char character, void* arg), void* arg, const char* format, ...);
+
+
+#ifdef __cplusplus
+}
+#endif
+
+
+#endif  // _PRINTF_H_