sunxi: increase SYS_MONITOR_LEN

[karo-tx-uboot.git] / doc / README.nand

diff --git a/doc/README.nand b/doc/README.nand
index b91f1985d183d0c3681567293cae7d666139a441..0ff56331d5f92ec1ba0dbea186e40d36b4a06cb2 100644 (file)
--- a/doc/README.nand
+++ b/doc/README.nand
@@ -89,18 +89,16 @@ Commands:
 
 Configuration Options:
 
+   CONFIG_SYS_NAND_U_BOOT_OFFS
+       NAND Offset from where SPL will read u-boot image. This is the starting
+       address of u-boot MTD partition in NAND.
+
    CONFIG_CMD_NAND
       Enables NAND support and commmands.
 
    CONFIG_CMD_NAND_TORTURE
       Enables the torture command (see description of this command below).
 
-   CONFIG_MTD_NAND_ECC_JFFS2
-      Define this if you want the Error Correction Code information in
-      the out-of-band data to be formatted to match the JFFS2 file system.
-      CONFIG_MTD_NAND_ECC_YAFFS would be another useful choice for
-      someone to implement.
-
    CONFIG_SYS_MAX_NAND_DEVICE
       The maximum number of NAND devices you want to support.
 
@@ -208,6 +206,14 @@ Platform specific options
        detection. However ECC calculation on such plaforms would still be
        done by GPMC controller.
 
+   CONFIG_SPL_NAND_AM33XX_BCH
+       Enables SPL-NAND driver (am335x_spl_bch.c) which supports ELM based
+        hardware ECC correction. This is useful for platforms which have ELM
+       hardware engine and use NAND boot mode.
+       Some legacy platforms like OMAP3xx do not have in-built ELM h/w engine,
+       so those platforms should use CONFIG_SPL_NAND_SIMPLE for enabling
+        SPL-NAND driver with software ECC correction support.
+
    CONFIG_NAND_OMAP_ECCSCHEME
        On OMAP platforms, this CONFIG specifies NAND ECC scheme.
        It can take following values:
@@ -231,16 +237,57 @@ Platform specific options
                8-bit BCH code with
                - ecc calculation using GPMC hardware engine,
                - error detection using ELM hardware engine.
+       OMAP_ECC_BCH16_CODE_HW
+               16-bit BCH code with
+               - ecc calculation using GPMC hardware engine,
+               - error detection using ELM hardware engine.
+
+       How to select ECC scheme on OMAP and AMxx platforms ?
+       -----------------------------------------------------
+       Though higher ECC schemes have more capability to detect and correct
+       bit-flips, but still selection of ECC scheme is dependent on following
+       - hardware engines present in SoC.
+               Some legacy OMAP SoC do not have ELM h/w engine thus such
+               SoC cannot support BCHx_HW ECC schemes.
+       - size of OOB/Spare region
+               With higher ECC schemes, more OOB/Spare area is required to
+               store ECC. So choice of ECC scheme is limited by NAND oobsize.
+
+       In general following expression can help:
+               NAND_OOBSIZE >= 2 + (NAND_PAGESIZE / 512) * ECC_BYTES
+       where
+               NAND_OOBSIZE    = number of bytes available in
+                               OOB/spare area per NAND page.
+               NAND_PAGESIZE   = bytes in main-area of NAND page.
+               ECC_BYTES       = number of ECC bytes generated to
+                               protect 512 bytes of data, which is:
+                               3 for HAM1_xx ecc schemes
+                               7 for BCH4_xx ecc schemes
+                               14 for BCH8_xx ecc schemes
+                               26 for BCH16_xx ecc schemes
+
+               example to check for BCH16 on 2K page NAND
+               NAND_PAGESIZE = 2048
+               NAND_OOBSIZE = 64
+               2 + (2048 / 512) * 26 = 106 > NAND_OOBSIZE
+               Thus BCH16 cannot be supported on 2K page NAND.
+
+               However, for 4K pagesize NAND
+               NAND_PAGESIZE = 4096
+               NAND_OOBSIZE = 64
+               ECC_BYTES = 26
+               2 + (4096 / 512) * 26 = 210 < NAND_OOBSIZE
+               Thus BCH16 can be supported on 4K page NAND.
+
+
+    CONFIG_NAND_OMAP_GPMC_PREFETCH
+       On OMAP platforms that use the GPMC controller
+       (CONFIG_NAND_OMAP_GPMC_PREFETCH), this options enables the code that
+       uses the prefetch mode to speed up read operations.
 
 NOTE:
 =====
 
-The current NAND implementation is based on what is in recent
-Linux kernels.  The old legacy implementation has been removed.
-
-If you have board code which used CONFIG_NAND_LEGACY, you'll need
-to convert to the current NAND interface for it to continue to work.
-
 The Disk On Chip driver is currently broken and has been for some time.
 There is a driver in drivers/mtd/nand, taken from Linux, that works with
 the current NAND system but has not yet been adapted to the u-boot