eeprog: Increase sleep between byte writes

Increese sleep time between writes to accomodate typical write
cycle times. An Atmel AT24C02 as well as an ON Semiconductor
CAT24C02 EEPROM specify 5ms. This resolves errors such as:

  ...
    Bus: /dev/i2c-1, Address: 0x50, Mode: 8bit
    Writing stdin starting at address 0x0
  ..Error i2c_write_2b: Input/output error
  Error at line 162: write error

[JD] Define a single constant and add a note that this could be
     revisited.

CHANGES

@@ -46,6 +46,7 @@ SVN HEAD
   decode-vaio: Add a manual page
   eeprog: Add a manual page
           Moved to a separate subdirectory
+          Increase delay after writes
   eeprom: Add a manual page
           Marked as deprecated
   eepromer: Add a manual page

eeprog/24cXX.c

@@ -26,6 +26,13 @@
 #include <i2c/smbus.h>
 #include "24cXX.h"
 
+/*
+ * EEPROMs need some time to process writes
+ * Ideally this value should either be settable with a command line parameter,
+ * or "guessed" at runtime using a retry loop.
+ */
+#define WRITE_DELAY_US		5000
+
 static int i2c_write_1b(struct eeprom *e, __u8 buf)
 {
 	int r;
@@ -33,7 +40,7 @@ static int i2c_write_1b(struct eeprom *e, __u8 buf)
 	r = i2c_smbus_write_byte(e->fd, buf);
 	if(r < 0)
 		fprintf(stderr, "Error i2c_write_1b: %s\n", strerror(errno));
-	usleep(10);
+	usleep(WRITE_DELAY_US);
 	return r;
 }
 
@@ -44,7 +51,7 @@ static int i2c_write_2b(struct eeprom *e, __u8 buf[2])
 	r = i2c_smbus_write_byte_data(e->fd, buf[0], buf[1]);
 	if(r < 0)
 		fprintf(stderr, "Error i2c_write_2b: %s\n", strerror(errno));
-	usleep(10);
+	usleep(WRITE_DELAY_US);
 	return r;
 }
 
@@ -56,7 +63,7 @@ static int i2c_write_3b(struct eeprom *e, __u8 buf[3])
 	r = i2c_smbus_write_word_data(e->fd, buf[0], buf[2] << 8 | buf[1]);
 	if(r < 0)
 		fprintf(stderr, "Error i2c_write_3b: %s\n", strerror(errno));
-	usleep(10);
+	usleep(WRITE_DELAY_US);
 	return r;
 }