diff --git a/ChangeLog b/ChangeLog
index 79e590904a..1d8d2664df 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -5534,4 +5534,7 @@
 	  definition file (2013-9-11).
 	* arch/arm/src/sama5/sam_twi.c and .h:  Framework for a SAMA5
 	  TWI driver (not much present in initial checkin) (2013-9-11).
+	* fs/nxffs:  Clean up some compilation warnings (2013-9-12)
+	* drivers/mtd/at24xx.c:  Add support for the AT 24C512 part
+	  (2013-9-12).
 
diff --git a/drivers/mtd/Kconfig b/drivers/mtd/Kconfig
index 01d488cd6c..ffe7ac06e1 100644
--- a/drivers/mtd/Kconfig
+++ b/drivers/mtd/Kconfig
@@ -67,22 +67,28 @@ config RAMMTD_FLASHSIM
 endif
 
 config MTD_AT24XX
-	bool "I2C-based AT24XX eeprom"
+	bool "I2C-based AT24xx eeprom"
 	default n
 	select I2C
 	---help---
-		Build support for I2C-based at24cxx EEPROM(at24c32, at24c64,
+		Build support for I2C-based AT24CXX EEPROM(at24c32, at24c64,
 		at24c128, at24c256)
 
 if MTD_AT24XX
 
 config AT24XX_SIZE
-	int "at24xx size(kByte)"
+	int "AT24xx size (kbit)"
 	default 64
+		---help---
+		This is the XX in the AT24Cxx part number.  For example, if you have a
+		AT 24C512, then the correct value is 512.  This value is also the capacity
+		of the part in kilobits.  For example, the 24C512 supports 512 Kbits or
+		512 /8 = 64 KiB.
 
 config AT24XX_ADDR
-	hex "at24xx i2c address"
+	hex "AT24XX I2C address"
 	default 0x50
+	range 0x50 0x57
 
 endif
 
diff --git a/drivers/mtd/at24xx.c b/drivers/mtd/at24xx.c
index 2eb7c9af08..326c6f86b2 100644
--- a/drivers/mtd/at24xx.c
+++ b/drivers/mtd/at24xx.c
@@ -1,6 +1,6 @@
 /************************************************************************************
  * drivers/mtd/at24xx.c
- * Driver for I2C-based at24cxx EEPROM(at24c32,at24c64,at24c128,at24c256)
+ * Driver for I2C-based at24cxx EEPROM(at24c32,at24c64,at24c128,at24c256,at24c512)
  *
  *   Copyright (C) 2011 Li Zhuoyi. All rights reserved.
  *   Author: Li Zhuoyi <lzyy.cn@gmail.com>
@@ -81,21 +81,24 @@
 
 /* Get the part configuration based on the size configuration */
 
-#if CONFIG_AT24XX_SIZE == 32
+#if CONFIG_AT24XX_SIZE == 32      /* AT24C32: 32Kbits = 4KiB; 128 * 32 =  4096 */
 #  define AT24XX_NPAGES     128
 #  define AT24XX_PAGESIZE   32
-#elif CONFIG_AT24XX_SIZE == 48
+#elif CONFIG_AT24XX_SIZE == 48    /* AT24C48: 48Kbits = 6KiB; 192 * 32 =  6144 */
 #  define AT24XX_NPAGES     192
 #  define AT24XX_PAGESIZE   32
-#elif CONFIG_AT24XX_SIZE == 64
+#elif CONFIG_AT24XX_SIZE == 64    /* AT24C64: 64Kbits = 8KiB; 256 * 32 = 8192 */
 #  define AT24XX_NPAGES     256
 #  define AT24XX_PAGESIZE   32
-#elif CONFIG_AT24XX_SIZE == 128
+#elif CONFIG_AT24XX_SIZE == 128   /* AT24C128: 128Kbits = 16KiB; 256 * 64 = 16384 */
 #  define AT24XX_NPAGES     256
 #  define AT24XX_PAGESIZE   64
-#elif CONFIG_AT24XX_SIZE == 256
+#elif CONFIG_AT24XX_SIZE == 256   /* AT24C256: 256Kbits = 32KiB; 512 * 64 = 32768 */
 #  define AT24XX_NPAGES     512
 #  define AT24XX_PAGESIZE   64
+#elif CONFIG_AT24XX_SIZE == 512   /* AT24C512: 512Kbits = 64KiB; 512 * 128 = 65536 */
+#  define AT24XX_NPAGES     512
+#  define AT24XX_PAGESIZE   128
 #endif
 
 /* For applications where a file system is used on the AT24, the tiny page sizes
@@ -139,8 +142,10 @@ static ssize_t at24c_bread(FAR struct mtd_dev_s *dev, off_t startblock,
                            size_t nblocks, FAR uint8_t *buf);
 static ssize_t at24c_bwrite(FAR struct mtd_dev_s *dev, off_t startblock,
                             size_t nblocks, FAR const uint8_t *buf);
+#if 0 /* Not implemented */
 static ssize_t at24c_read(FAR struct mtd_dev_s *dev, off_t offset,
                           size_t nbytes,FAR uint8_t *buffer);
+#endif
 static int at24c_ioctl(FAR struct mtd_dev_s *dev, int cmd, unsigned long arg);
 
 /************************************************************************************