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Questions about Boot form SD card for C5535

George Lin
Prodigy 90 points
Other Parts Discussed in Thread: CSD

Hello Everyone,

I have 2 questions about booting from SD card after reading data sheet of C5535.

9.  Test for eMMC partitions/eMMC/SD0 boot:
–   For an eMMC/SD/SDHC card, the card must be formatted to FAT16 or FAT32. The boot image file
must be renamed to "bootimg.bin" and copied to the foot directory of the formatted card.
–   If an eMMC boot partition is desired (for only eMMC 4.3 and up), then the boot image file must be
programmed to one of the two boot partitions (1 or 2) on the eMMC card. PARTITION_CONFIG in
the EXT_CSD must be set accordingly.
–   If the boot signature is found, attempt eMMC/SD/SDHC boot and go to step 13.
If boot signature is not found, go to step 10.

My questions  are

1.)  What is the limitation for  boot image file size?  Does it depend on SARAM size  ( 256K  Bytes  in C5535 )

2.)  If I make SD card into  2 partitions , which partition I could put  bootimg.bin for SD boot ?

George

  • 0
    Guru 31670 points

    George,

    1. The file size limitation will almost be equal to SARAM size. If the BOOTROM code uses this SARAM for for its data/bss/stack usage you've to subtract that. I'm not sure about C5535 whether it uses SARAM for BOOTROM memory requirements and the size used. It will most likely be less than 10KB.

    2. The first partition is the boot partition.

  • 0 in reply to Renjith Thomas
    Prodigy 90 points

    Renjith,

    Thank you for your reply .

    And I see a note on datasheet. "SARAM31 (byte address range: 0x4E000 – 0x4EFFF) is reserved for the bootloader. After the boot process is complete, this memory space can be used."


  • 0 in reply to George Lin
    Guru 31670 points

    George,

    Its clear now. 4KB is reserved for BOOTROM's data area. If you are greedy :) and want to make use of this space also, there is a method. You can link you BSS segment to this area and initialize BSS at run-time. So, that 4KB also will be yours :)