diff --git a/src/hos_printf.c b/src/hos_printf.c
index 681d3b6..6013d53 100644
--- a/src/hos_printf.c
+++ b/src/hos_printf.c
@@ -60,11 +60,38 @@ static size_t format_hex(char * buffer, int v, bool upper)
     return sz;
 }
 
+static void pad_write(const stream_t * stream, const char * data, size_t length, bool leading_zero, bool left_just, size_t width)
+{
+    if (left_just)
+    {
+        stream->write(data, length);
+        while (length < width)
+        {
+            stream->write1(' ');
+            length++;
+        }
+    }
+    else
+    {
+        char fill = leading_zero ? '0' : ' ';
+        size_t l = length;
+        while (l < width)
+        {
+            stream->write1(fill);
+            l++;
+        }
+        stream->write(data, length);
+    }
+}
+
 void hos_vprintf(const stream_t * stream, const char * fmt, va_list va)
 {
     bool in_conv = false;
     char c;
     char buffer[12];
+    size_t width;
+    bool leading_zero;
+    bool left_just;
     while ((c = *fmt))
     {
         if (in_conv)
@@ -78,40 +105,40 @@ void hos_vprintf(const stream_t * stream, const char * fmt, va_list va)
                 {
                     unsigned int v = va_arg(va, unsigned int);
                     size_t length = format_hex(buffer, v, true);
-                    stream->write(buffer, length);
+                    pad_write(stream, buffer, length, leading_zero, left_just, width);
                 }
                 break;
             case 'c':
                 {
                     char ch = va_arg(va, int);
-                    stream->write1(ch);
+                    pad_write(stream, &ch, 1u, leading_zero, left_just, width);
                 }
                 break;
             case 'd':
                 {
                     int v = va_arg(va, int);
                     size_t length = format_dec(buffer, v);
-                    stream->write(buffer, length);
+                    pad_write(stream, buffer, length, leading_zero, left_just, width);
                 }
                 break;
             case 's':
                 {
                     const char * s = va_arg(va, const char *);
-                    stream->write(s, strlen(s));
+                    pad_write(stream, s, strlen(s), leading_zero, left_just, width);
                 }
                 break;
             case 'u':
                 {
                     unsigned int v = va_arg(va, unsigned int);
                     size_t length = format_udec(buffer, v);
-                    stream->write(buffer, length);
+                    pad_write(stream, buffer, length, leading_zero, left_just, width);
                 }
                 break;
             case 'x':
                 {
                     unsigned int v = va_arg(va, unsigned int);
                     size_t length = format_hex(buffer, v, false);
-                    stream->write(buffer, length);
+                    pad_write(stream, buffer, length, leading_zero, left_just, width);
                 }
                 break;
             }
@@ -120,6 +147,25 @@ void hos_vprintf(const stream_t * stream, const char * fmt, va_list va)
         else if (c == '%')
         {
             in_conv = true;
+            width = 0u;
+            leading_zero = false;
+            left_just = false;
+            if (fmt[1] == '-')
+            {
+                left_just = true;
+                fmt++;
+            }
+            if (fmt[1] == '0')
+            {
+                leading_zero = true;
+                fmt++;
+            }
+            while (('0' <= fmt[1]) && (fmt[1] <= '9'))
+            {
+                width *= 10u;
+                width += (fmt[1] - '0');
+                fmt++;
+            }
         }
         else
         {