@sandungas
It doesn't have much to do with the current discussion, but I have to ask, is it possible to overwrite Syscon, as is done on the NAND/NOR chip? I ask because, when you change the PS3 processor, the NOR you can just rewrite it using the patch compatible with the new CPU, but what about Syscon, is it possible to do that or are we not there yet?
Depends of the memory type, the syscon is like a tiny computer with several memories inside, is better seen on this table
https://www.psdevwiki.com/ps3/Syscon_Hardware#PS3_Syscon_models
This needs to be explained starting with the retail mullion syscons (the CXR models without the "F") because are the most simples of all them
ROM is "read only", used to store the base syscon firmware so is unbrickable because is phisically imposible to write in it, a convenient consequence of this is we are using the syscon firmware identifyers to identify the syscon model (hardware) because every hardware revision have a unique syscon firmware, to read the ROM is used an exploit that allows to read it entirelly, for curiosity sake... if you take a look at some of the syscon dumps shared publically you are going to realize they have the exact same size mentioned in that table in wiki
The EEPROM is "read & write" access, is intended to store settings, and other stuff that requires to be updated frequently (like the error logs, or the bringup/shutdowns/runtime counters), most of the EEPROM is available to be readen/written when we do a standard auth access by UART, this can be seen in this other table, as you can see there are some areas marked with the tag "exploit" because are protected
https://www.psdevwiki.com/ps3/Talk:SC_EEPROM#Experimental_table
In the mullion syscons (all the ones soldered by BGA) there are a few BGA pads that are a direct SPI access to the EEPROM, this means we can read/write the EEPROM entirelly if we connect an external programmer to that EEPROM pads, this is usually made with a programmer named "bus pirate"
The RAM is like the RAM of a PC, when the syscon boots it loads parts of the ROM and EEPROM into RAM... then it uses the data from RAM (instead of the original). This feature is used in the official syscon patches, the patch is stored in EEPROM, but is applyed over the copy of the ROM data in RAM
----------
The FLASH of the "F" syscon is an special feature, as you can see in the first table, the size of FLASH is exactly the same than the ROM of the other mullion syscon models... because the FLASH is inteded to store the base firmware
In other words... you can take the ROM data from a different syscon model and write it in the "FLASH" area of the "F" syscon and the result would be like using the syscon that was a donor of the ROM data
---------
The sherwood syscons are trying to keep some "backward compatibility" with the previous syscons, but there is not an EEPROM anymore (and there are no pads/pins to access it externally)
The syscon base firmware is stored in FLASH, and the data that was stored in EEPROM from the previous versions is stored in FLASH too, all together
Is a more simple design because there is only 1 storage memory type, and technically is full read & write access... as far i know there is not a known way to write it entirelly, but we can read it entirelly with exploits
One of the features related with that "backward compatibility" i mentioned is, when the sherwoods boots they are "emulating" a "virtual" EEPROM that have the same exact size than the previous mullion syscons... but the way how the data is organized inside that virtual EEPROM is weird in many senses because if like it is created "on the fly" by joining together various pieces of data from different parts of the FLASH
The results is the contents of that virtual EEPROM is not exactly like in the previous mullion syscons, this sucks a bit for sherwood owners because most of the R&D work was made in mullions, obviouslly (specially with the help of the "F" syscon, extremelly convenient to do experiments)
-----------------
So long story short... yeah, in mullions we can read them entirelly, and write them entirelly except the syscon base firmware stored in ROM (but we can apply "on the fly" patches in the ROM)
Sherwoods have the potential of being able to read/write everything, included the syscon base firmware, but as far i know there is no known way to do it, we can read the FLASH entirelly, but we can only write in some specific areas of it :/