(2x) speed increase in printFloat() function. Decimal places setting added.

- printFloat() function execution doubled in speed. This is a precursor
to status reporting, since GUIs may query real-time position rapidly.

- Decimal places added to settings (for now). This may disappear in
future pushes, but here for testing purposes.

print.c

@@ -27,6 +27,7 @@
 #include <avr/pgmspace.h>
 #include "config.h"
 #include "serial.h"
+#include "settings.h"
 
 void printString(const char *s)
 {
@@ -88,12 +89,12 @@ static void print_uint32_base10(unsigned long n)
   } 
   
   while (n > 0) {
-    buf[i++] = n % 10;
+    buf[i++] = n % 10 + '0';
     n /= 10;
   }
     
   for (; i > 0; i--)
-    serial_write('0' + buf[i - 1]);
+    serial_write(buf[i-1]);
 }
 
 void printInteger(long n)
@@ -105,27 +106,43 @@ void printInteger(long n)
   print_uint32_base10(n);
 }
 
-void printFloat(double n)
+// Convert float to string by immediately converting to a long integer, which contains
+// more digits than a float. Number of decimal places, which are tracked by a counter,
+// may be set by the user. The integer is then efficiently converted to a string.
+void printFloat(float n)
 {
   if (n < 0) {
     serial_write('-');
     n = -n;
   }
-  n += 0.5/DECIMAL_MULTIPLIER; // Add rounding factor
 
-  long integer_part;
-  integer_part = (int)n;
-  print_uint32_base10(integer_part);
-  
-  serial_write('.');
-  
-  n -= integer_part;
-  int decimals = DECIMAL_PLACES;  
-  uint8_t decimal_part;  
-  while(decimals-- > 0) {
-    n *= 10;
-    decimal_part = (int) n;
-    serial_write('0'+decimal_part);
-    n -= decimal_part;
+  uint8_t decimals = settings.decimal_places;
+  while (decimals >= 2) { // Quickly convert values expected to be E0 to E-4.
+    n *= 100;
+    decimals -= 2;
   }
+  if (decimals) { n *= 10; }
+  n += 0.5; // Add rounding factor. Ensures carryover through entire value.
+    
+  // Generate digits backwards and store in string.
+  unsigned char buf[10]; 
+  uint8_t i = 0;
+  uint32_t a = (long)n;  
+  buf[settings.decimal_places] = '.'; // Place decimal point, even if decimal places are zero.
+  while(a > 0) {
+    if (i == settings.decimal_places) { i++; } // Skip decimal point location
+    buf[i++] = (a % 10) + '0'; // Get digit
+    a /= 10;
+  }
+  while (i < settings.decimal_places) { 
+     buf[i++] = '0'; // Fill in zeros to decimal point for (n < 1)
+  }
+  if (i == settings.decimal_places) { // Fill in leading zero, if needed.
+    i++;
+    buf[i++] = '0'; 
+  }   
+  
+  // Print the generated string.
+  for (; i > 0; i--)
+    serial_write(buf[i-1]);
 }

settings.c

@@ -77,6 +77,7 @@ typedef struct {
 // #define DEFAULT_AUTO_START 1 // true
 // #define DEFAULT_INCHES_MODE 1 // true
 // #define DEFAULT_BLOCK_DELETE 0  // false
+#define DEFAULT_DECIMAL_PLACES 3
 
 void settings_reset(bool reset_all) {
   // Reset all settings or only the migration settings to the new version.
@@ -101,6 +102,7 @@ void settings_reset(bool reset_all) {
   settings.homing_seek_rate = DEFAULT_HOMING_RAPID_FEEDRATE;
   settings.homing_debounce_delay = DEFAULT_HOMING_DEBOUNCE_DELAY;
   settings.stepper_idle_lock_time = DEFAULT_STEPPER_IDLE_LOCK_TIME;
+  settings.decimal_places = DEFAULT_DECIMAL_PLACES;
 }
 
 void settings_dump() {
@@ -120,7 +122,8 @@ void settings_dump() {
   printPgmString(PSTR(" (mm/min homing feed rate)\r\n$12 = ")); printFloat(settings.homing_seek_rate);
   printPgmString(PSTR(" (mm/min homing seek rate)\r\n$13 = ")); printInteger(settings.homing_debounce_delay);
   printPgmString(PSTR(" (milliseconds homing debounce delay)\r\n$14 = ")); printInteger(settings.stepper_idle_lock_time);
-  printPgmString(PSTR(" (milliseconds stepper idle lock time)")); 
+  printPgmString(PSTR(" (milliseconds stepper idle lock time)\r\n$15 = ")); printInteger(settings.decimal_places);
+  printPgmString(PSTR(" (float decimal places)")); 
   printPgmString(PSTR("\r\n'$x=value' to set parameter or just '$' to dump current settings\r\n"));
 }
 
@@ -235,6 +238,7 @@ void settings_store_setting(int parameter, float value) {
     case 12: settings.homing_seek_rate = value; break;
     case 13: settings.homing_debounce_delay = round(value); break;
     case 14: settings.stepper_idle_lock_time = round(value); break;
+    case 15: settings.decimal_places = round(value); break;
     default: 
       printPgmString(PSTR("Unknown parameter\r\n"));
       return;

settings.h

@@ -29,7 +29,7 @@
 
 // Version of the EEPROM data. Will be used to migrate existing data from older versions of Grbl
 // when firmware is upgraded. Always stored in byte 0 of eeprom
-#define SETTINGS_VERSION 51
+#define SETTINGS_VERSION 52
 
 // Define bit flag masks in settings.flag.
 #define FLAG_BIT_HOMING_ENABLE      bit(0)
@@ -52,6 +52,7 @@ typedef struct {
   float homing_seek_rate;
   uint16_t homing_debounce_delay;
   uint8_t stepper_idle_lock_time;
+  uint8_t decimal_places;
 } settings_t;
 extern settings_t settings;