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What is the exact purpose of CS0BW ?

Wonhong Kwon
Intellectual 260 points

Hi All,

According to Datasheet, CS0BW is defined to "GPMC CS0 default data bus width input." I have EVM + VS daughter board and Micron NAND(16-bit) / Spansion NOR(16-bit) are equipped on them. I think CS0BW should be set to '1' (16-bit data bus) for those devices but recommended configuration (described in TI816x-PSP-04.00.00.09-U-boot) is CS0BW = 0 for NAND and CS0BW = 1 for NOR.

With this in mind, now I'm confusing that what CS0BW value should be used for our custom board. On our board, 8-bit NOR device is equipped.

Regards,
Wonhong

  • 0
    TI__Expert 6175 points

    Wonhong,

     

    This pin directly sets a bit in the GPMC controller, that configure the controller to talk to a 16 bit device or 8 bit device. In the GPMC controller register, this bit can be overwritten in s/w based on the device you are accessing - so for s/w this bit can be set depending on the kind of device you are using. The importance of this bit is more from a boot perspective, as the ROM does not touch this bit and expects the user to configure this pin propely based on the device he has on his board.

    If you are using an 8 bit NOR device, this bit should be set to 0, if you want to boot from it. You will also have to change the GPMC configuration in u-boot as you are using an 8-bit NOR device.

    Regards,

    Madan

  • 0 in reply to Madans
    Intellectual 260 points

    Hi Madan,

    The register you kept refering to is GPMC_CONFIG1[13:12] (DEVICESIZE) ? If then, you mean that I need to set CS0BW to LOW and this register to 0b'00. Am I right ?

    Extra Query:
    As far as I understand, MASKADDRESS and BASEADDRESS bit in GPMC_CONFIG7 should be set based on the size of the external device. In our custom board, 512 KB 8-bit NOR is equipped and I'm confusing which value is set to those bits because the size of the NOR is less than 16 MB.
    Could you give me some advices for this ?

  • 0 in reply to Wonhong Kwon
    TI__Expert 6175 points

    Wonhong,

    Yes, you are right. You can set it to 16MB as you are using a small NOR flash. All that will happen is that the memory map will reserve 16 MB from the base address for NOR access - for yo onlt the first 512KB will be valid - any access beyond this will simply return garbage. Is the device type muxed or non-muxed?

    Regards,

    Madan

  • 0 in reply to Madans
    Intellectual 260 points

    Madan,

    Then, MASKADDRESS and BASEADDRESS can be set to 0b'1111 (0xF: CS size is 16 MB) and 0b'00000 (0x00) respectively ?
    By the way, the device is non-muxed type.

    Thanks,
    Wonhong