[coreboot] Firmware hub flash addressing [off-topic]

Marc Jones Marc.Jones at amd.com
Tue Jun 17 19:38:58 CEST 2008

llandre wrote:
>> Sorry for posting a message that is a little bit off-topic.
>> I'm working with a SST 8 Mbit Firmware Hub SST49LF008A flash connected 
>> to Geode LX LPC bus.
>> I need to understand where flash registers are mapped in case the flash 
>> ID is set to 1 (this flash is not the boot flash that has ID=0).
>> The datasheet just says about identification registers (same thing 
>> applies for other registers too):
>> JEDEC ID Registers
>> The JEDEC ID registers for the boot device appear at
>> FFBC0000H and FFBC0001H in the 4 GByte system
>> memory map, and will appear ***elsewhere*** if the device is not
>> the boot device.
>> Anybody can tell me what does "elsewhere" stand for in this sentence?
> Some news ...
> If I understand correctly, "elsewhere" is not defined by LPC/FirmwareHub 
> standard but it depends on LPC controller (that's why it is not 
> specified in flash datasheet). On GeodeLX/CS5536, when reading location 
> at 0xFFBC0000, CS5536 generates a Firmware Hub Memory Read cycle with 
> IDSEL=0 (I verified this with a logic analyzer connected to LPC bus). I 
> tried to access different locations but I was not able to make CS5536 to 
> generate read cycles with IDSEL different from 0. So I don't understand 
> how the physical addresses are related to the IDSEL that is sent on the 
> LPC bus by CS5536. Anybody can help?


Sorry, the 5536 only sets IDSEL = 0 for FWH.  But, I think you can 
design in multiple LPC ROMs.

The LPC ROMs should have ID pins that map them to different regions, 
i.e. there's an internal compare for the inverted values to certain 
address bits.  So it seems you should be able to map multiple devices in 
the address space this way.

See page 10 -


Marc Jones
Senior Firmware Engineer
(970) 226-9684 Office
mailto:Marc.Jones at amd.com

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