Hello All,
I am having a rather curious problem with using NAND flash on the AMCC 440EP.
My platform boots entirely from NAND Flash, as such, I have modified U-Boot to run from SDRAM and created a small Bootloader that initializes the board and loads U-Boot from NAND to SDRAM where it sets U-Boot running.
I've gotten it to a state where I can load U-Boot via a debugger (RiscWatch) into SDRAM and program NAND with both my small bootloader and U-Boot. This all works.
Now when U-Boot is loaded from NAND to SDRAM using a small bootloader it cannot read the Manufacturer or Chip ID from the NAND flash chip so it bails out. This does not happen when loading the exact same U-Boot image from the RiscWatch to SDRAM and running it.
Using a LogicAnalyzer, I have narrowed down the problem to something that has me stumped that I hope someone here can help me with or point me in the right direction.
The Code in common/cmd_nand.c that identifies the chip basically does the following:
Resets NAND. Waits for NAND to become READY Write READ ID Command Writes Address byte 0 Read Manfacturer ID Read Chip ID
When loaded under the RiscWatch we see the following: CLE pulses as WE pulses [Reset of NAND Chip] READY goes low READY goes high (approx 120ns after going low) CLE pulses as WE pulses [READ ID Command] ALE pulses as WE Pulses [Write Address byte 0] 2 Read Pulses
This is as expected and all works.
When loaded under the bootloader from NAND we see the following: 4 Read Pulses CLE pulses as WE pulses [Reset of NAND Chip] READY goes low READY goes high (approx 120ns after going low) CLE pulses as WE pulses [READ ID Command] ALE pulses as WE Pulses [Write Address byte 0]
This is un-expected and does not work. I did not expect the 4 read pulses, and there are absolutly no read pulses (like the 2 expected) after we write the address byte 0.
Does anyone have any ideas as to what could be going wrong? Any help is greatly appreciated.