Hi...
On the eoma68 spec it says:
"The EEPROM MUST NOT be used for the storage of user data: it is reserved exclusively for EOMA-68."
My understanding from past threads on the matter is that currently the only specified usage for this by EOMA-68 is a product ID string + device node tree. It would be most useful if there was a definition on the layout. *cough* A defined data structure allowing for future expansion as well as vendor specific additions would be golden.
A simple page based system would suffice afaics. Sth like:
Address Size Value ====== === ==== 0x00 2 Page identifier (defined by EOMA68 spec) 0x02 2 Size of page data 0x06 val 0x02 Page data
Page data would (obviously) be limited to a maximum 64k in size, but that really should not be an issue given the application (and given how much data you can read at a time via i2c_smbus calls). A checksum could be added to the page header if desired to verify the data read in, but that could also be left to the page specific data. I don’t think a checksum is needed for the device ID page, for instance.
Page identifiers would be things like: "0x01 Device ID".
A simple, sequential page ordering would to make it easy to use a function lookup table to parse the data. Page 0x00 would be a special “there are no more pages” id.
The page ID # space could be split in 2 between EOMA68 and vendor, giving 32768 possible page IDs to both (far more than necessary, but 1 byte isn’t enough, and i don’t see any benefit to trying to pack bytes together and bit twiddling on the software side to unpack them). this would have the nice characteristic of any page id with the high bit set to 1 would be a vendor page.
The device ID page data definition might look sth like:
Size in Byte(s) Value ========== ====================== 2 Device type (assigned centrally) 2 Device revision 4 Vendor ID (assigned centrally) 4 Product ID (vendor generated, registered centrally) N Manufacturer cstring N Product cstring N Serial number cstring
A set of defined pages would be marked as REQUIRED and standard page IDs would be defined as well. I’d actually recommend this definition to be housed *outside* of the EOMA68 spec so that it can be used more broadly by the open hardware community (where such things seem non-existent) and to keep the EOMA68 spec from becoming too monstrous.
This approach would have a number of advantages imo:
* quick access to any given page without lots of index overhead (just jump through the page headers) * minimum size is self documenting: all REQUIRED pages (e.g. device ID page) become the minimum size for the EEPROM on the device * It avoids (imho) stupid hard coded lengths; it’s no longer 1985, even in the embedded world people and many/most of the products we’re working on have application class processors, and even the ones with “just” microcontrolers can do a hell of a lot such that hard coded page sizes just don’t make sense * It allows some vendor flexibility
I am willing to write a small C library that takes a well formed set of data, parses all the EOMA68 bits and offers nice API to access things like device ID data, keeping implementation details at arms length from applications. I could also provide a tool that takes a descriptor file in a human readable format and converts it into a proper EOMA68 packed structure to be written to an EEPROM. Obviously we need agreement on the above before I do this.
Some additional semi-random notes from reading the EOMA68 spec regarding the EEPROM:
In the "Start-up procedure” section, it gives the EEPROM address as 0xA2 rather than 0x51. I would recommend not putting the address here, but rather dealing with all those details in the "Requirements for I2C” section and giving the EEPROM a proper name there (e.g. the RID EEPROM, for Required IDentification).
In fact, I’d re-org that section entirely to be like:
Required Interfaces Rational for interface selections* i2c The "Required IDentification” EEPROM USB SATA ETHERNET RGB/TTL
* I would remove all mention of specific vendors here; this is a specification after all, so I’d kill the last para about All Winner and costing. I would also move each of the line items about the interfaces to the section on that interface
Thoughts?