Flash memory - Revision history

Michael: /* Data Locations */ re wiki-linked TRX header

2009-07-29T18:10:53Z

Data Locations: re wiki-linked TRX header

Michael: /* NVRAM */ Added disclaimer about header

2009-07-29T18:08:27Z

NVRAM: Added disclaimer about header

Michael: Created more extensive Flash memory page

2009-07-29T18:06:59Z

Created more extensive Flash memory page

Michael: Created page for flash memory

2009-07-29T01:29:13Z

Created page for flash memory

New page

[[Image:Flash_memory.png|thumb|150px|right|Quick reference guide to Flash memory on XINU.]]
Unlike other devices on the system Flash memory is fully mapped, meaning it is possible to access every location of the four megabyte range by simply dereferencing a pointer between <tt>0xBC00 0000</tt> and <tt>0xBC3F FFFF</tt>. Within Flash memory there are a number of notable addresses:
* <tt>0xBC00 1000</tt>: Generic backup NVRAM variables (if proper variables become corrupt, these are the values that will replace them).
* <tt>0xBC00 1E00</tt>: "True" MAC address of device, this is the mac address CFE will use during the boot process. Once the system is booted, the MAC address is not necessarily the same as the value stored here. The value is stored in ASCII as 6 colon separated octets for a total of 17 bytes.
* <tt>0xBC00 1F00</tt>: CFE Boot Version variable ("v3.7")
* <tt>0xBC00 2000</tt>: CFE code begins
* <tt>0xBC03 F400</tt>: Unique device ID, this is loaded into NVRAM variables as eou_device_id
* <tt>0xBC03 F408</tt>: Private key for device, also loaded into NVRAM variables as eou_private_key
* <tt>0xBC03 F508</tt>: Public key for device, also loaded into NVRAM variables as eou_public_key
* <tt>0xBC04 0000</tt>: XINU code, gzipped raw binary prefixed with a TRX header containing the length and a checksum among other data.
* <tt>0xBC06 0000</tt>: Beginning of XINU file system
* <tt>0xBC3F 8000</tt>: NVRAM variables are stored here, prefix with a padded length and checksum among other data for a 20 byte header. Each variable is stored as a name=value pair (as ASCII data) and separated by a single null character.

@@ Line 13: / Line 13: @@
 * <tt>0xBC03 F408</tt> is a unique private key for device (should match the NVRAM setting for <code>eou_private_key</code>).
 * <tt>0xBC03 F508</tt> is a unique public key for device (should match the NVRAM setting for <code>eou_public_key</code>).
-* <tt>0xBC04 0000</tt> is the beginning of the operating system kernel ([[Embedded Xinu]] or some Linux variant).  Typically, this will be a gzipped version of the raw kernel code prefixed with a [[TRX]] header.
+* <tt>0xBC04 0000</tt> is the beginning of the operating system kernel ([[Embedded Xinu]] or some Linux variant).  Typically, this will be a gzipped version of the raw kernel code prefixed with a [[TRX header]].
 * <tt>0xBC3F 8000</tt> is the location of proper [[#NVRAM|NVRAM settings]].

@@ Line 45: / Line 45: @@
   |                        NCDL value (?)                         |
   +---------------------------------------------------------------+
 Immediately after the header begins the NVRAM settings as NULL delimited <code>name=value</code> tuples stored as plain text.  It is possible that after the final tuple the settings are NULL character padded to the nearest 4 byte word.

@@ Line 1: / Line 1: @@
-[[Image:Flash_memory.png|thumb|150px|right|Quick reference guide to Flash memory on XINU.]]
+Like other memory mapped hardware devices on the MIPS platform, Flash memory has an address range in KSEG1.  This means that the memory is '''unmapped''' and '''uncached'''.  An interesting, and important, piece of information is that all 4 megabytes of Flash memory is mapped 1-1 into the address range between <tt>0xBC00 0000</tt> and <tt>0xBC3F FFFF</tt>.  This allows for random read-access without using an interface to load the data a fixed amount of registers.
-Unlike other devices on the system Flash memory is fully mapped, meaning it is possible to access every location of the four megabyte range by simply dereferencing a pointer between <tt>0xBC00 0000</tt> and <tt>0xBC3F FFFF</tt>.  Within Flash memory there are a number of notable addresses:
-* <tt>0xBC00 1000</tt>: Generic backup NVRAM variables (if proper variables become corrupt, these are the values that will replace them).
-* <tt>0xBC00 1E00</tt>: "True" MAC address of device, this is the mac address CFE will use during the boot process.  Once the system is booted, the MAC address is not necessarily the same as the value stored here.  The value is stored in ASCII as 6 colon separated octets for a total of 17 bytes.
+== Data Locations ==
-* <tt>0xBC00 1F00</tt>: CFE Boot Version variable ("v3.7")
-* <tt>0xBC00 2000</tt>: CFE code begins
+Stored on Flash memory are several important parts to make a backend work properly, some of these data points are listed below.
-* <tt>0xBC03 F400</tt>: Unique device ID, this is loaded into NVRAM variables as eou_device_id
-* <tt>0xBC03 F408</tt>: Private key for device, also loaded into NVRAM variables as eou_private_key
+* <tt>0xBC00 1000</tt> has backup NVRAM settings. If the "proper" settings become corrupt, [[CFE]] will replace the proper settings with these.
-* <tt>0xBC03 F508</tt>: Public key for device, also loaded into NVRAM variables as eou_public_key
+* <tt>0xBC00 1E00</tt> holds the "true" MAC address of device.  During CFE boot, this is the address that will be used.  Once a full kernel has been loaded the MAC address may be different.
-* <tt>0xBC04 0000</tt>: XINU code, gzipped raw binary prefixed with a TRX header containing the length and a checksum among other data.
+* <tt>0xBC00 1F00</tt> holds the current CFE boot version (should be "v3.7" for [[WRT54GL|WRT54GLs]]).
-* <tt>0xBC06 0000</tt>: Beginning of XINU file system
+* <tt>0xBC00 2000</tt> is the beginning of CFE code.
-* <tt>0xBC3F 8000</tt>: NVRAM variables are stored here, prefix with a padded length and checksum among other data for a 20 byte header.  Each variable is stored as a name=value pair (as ASCII data) and separated by a single null character.
+* <tt>0xBC03 F400</tt> is a unique device ID (should match the NVRAM setting for <code>eou_device_id</code>).