Add external flash layout notes

README.md

@@ -19,6 +19,7 @@ Note that it also supports other Proxmark3 platforms as well!
 |[Issues](#issues)|[Blue shark manual](/doc/bt_manual_v10.md) |[Advanced compilation parameters](/doc/md/Use_of_Proxmark/4_Advanced-compilation-parameters.md)|
 |[Notes on UART](/doc/uart_notes.md)|||
 |[Notes on Frame format](/doc/new_frame_format.md)|||
+|[Notes on external flash](/doc/ext_flash_notes.md)|||
 |[Notes on Termux / Android](/doc/termux_notes.md)|||
 |[Developing standalone mode](/armsrc/Standalone/readme.md)|[Wiki about standalone mode](https://github.com/RfidResearchGroup/proxmark3/wiki/Standalone-mode) ||
 |[Donations](#Donations)|||

doc/ext_flash_notes.md

@@ -0,0 +1,95 @@
+# External flash
+
+External 256kbytes flash is a unique feature of the RDV4 edition.
+
+## Addresses
+
+Flash memory is
+
+* 256kb (0x40000= 262144)
+* divided into 4 pages of 64kb (0x10000 = 65536)
+* 4 pages divided into 16 sectors of 4kb (0x1000 = 4096), so last sector is at 0x3F000
+
+Therefore a flash address can be interpreted as such:
+```
+0xPSxxx       e.g. 0x3FF7F
+  ^ page             ^ page 3
+   ^ sector           ^ sector 0xF
+    ^^^ offset         ^^^ offset 0xF7F
+```
+
+## Layout
+
+Page 0:
+* available for user data
+* to dump it: `mem dump f page0_dump o 0 l 65536`
+* to erase it: `mem wipe p 0`
+
+Page 1:
+* available for user data
+* to dump it: `mem dump f page1_dump o 65536 l 65536`
+* to erase it: `mem wipe p 1`
+
+Page 2:
+* available for user data
+* to dump it: `mem dump f page2_dump o 131072 l 65536`
+* to erase it: `mem wipe p 2`
+
+Page 3:
+* used by Proxmark3 RDV4 specific functions: flash signature and keys dictionaries, see below for details
+* to dump it: `mem dump f page3_dump o 196608 l 65536`
+* to erase it:
+  * **Beware** it will erase your flash signature (see below) so better to back it up first as you won't be able to regenerate it by yourself!
+  * It's possible to erase completely page 3 by erase the entire flash memory with the voluntarily undocumented command `mem wipe i`.
+  * Updating keys dictionaries doesn't require to erase page 3.
+
+## Page3 Layout
+
+Page3 is used as follows by the Proxmark3 RDV4 firmware:
+
+* **MF_KEYS**
+  * offset: page 3 sector  9 (0x9) @ 3*0x10000+9*0x1000=0x39000
+  * length: 2 sectors
+
+* **ICLASS_KEYS**
+  * offset: page 3 sector 11 (0xB) @ 3*0x10000+11*0x1000=0x3B000
+  * length: 1 sector
+
+* **T55XX_KEYS**
+  * offset: page 3 sector 12 (0xC) @ 3*0x10000+12*0x1000=0x3C000
+  * length: 1 sector
+
+* **T55XX_CONFIG**
+  * offset: page 3 sector 13 (0xD) @ 3*0x10000+13*0x1000=0x3D000
+  * length: 1 sector (actually only a few bytes are used to store `t55xx_config` structure)
+
+* **RSA SIGNATURE**, see below for details
+  * offset: page 3 sector 15 (0xF) offset 0xF7F @ 3*0x10000+15*0x1000+0xF7F=0x3FF7F
+  * length: 128 bytes
+  * offset should have been 0x3FF80 but historically it's one byte off and therefore the last byte of the flash is unused
+
+## RSA signature
+
+To ensure your Proxmark3 RDV4 is not a counterfeit product, its external flash contains a RSA signature of the flash unique ID.
+You can verify it with: `mem info`
+
+```
+[usb] pm3 --> mem info
+          
+[=] --- Flash memory Information ---------
+          
+[=] -------------------------------------------------------------          
+[=] ID            | xx xx xx xx xx xx xx xx           
+[=] SHA1          | xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx           
+[=] RSA SIGNATURE |          
+[00] | xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx 
+[01] | xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx 
+[02] | xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx 
+[03] | xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx 
+[=] KEY length   | 128          
+[+] RSA key validation ok          
+[+] RSA Verification ok          
+```
+
+For a backup of the signature: `mem dump p f flash_signature_dump o 262015 l 128`
+