Electronic – SD card read sector problem

fatsdspi

I am using FatFS. After solving card initialization problem I am trying to read sector 0, but the card returns junk data.

This is my read operation:
enter image description here
I see that the card replied with 0x00 which means that it is read to deliver data.

Of course my zeroth sector dumped with a USB card reader looks correctly:
enter image description here

This is my debug log (CMD numbers are in hex):

    388:mmc_disk_initialize: SPI initialized
    366:send_cmd_INTERNAL: call 401 Cmd 00 response 01
    403:mmc_disk_initialize: CMD0 okay
    366:send_cmd_INTERNAL: call 405 Cmd 08 response 01
    406:mmc_disk_initialize: CMD8 okay - this is an SDv2 card
    409:mmc_disk_initialize: CMD8 response 000001AA
    413:mmc_disk_initialize: Waiting for leaving idle state
    366:send_cmd_INTERNAL: call 309 Cmd 37 response 01
    366:send_cmd_INTERNAL: call 415 Cmd 29 response 01
    366:send_cmd_INTERNAL: call 309 Cmd 37 response 01
    366:send_cmd_INTERNAL: call 415 Cmd 29 response 01
    366:send_cmd_INTERNAL: call 309 Cmd 37 response 01
    366:send_cmd_INTERNAL: call 415 Cmd 29 response 01
    366:send_cmd_INTERNAL: call 309 Cmd 37 response 01
    366:send_cmd_INTERNAL: call 415 Cmd 29 response 01
    366:send_cmd_INTERNAL: call 309 Cmd 37 response 01
    366:send_cmd_INTERNAL: call 415 Cmd 29 response 01
    366:send_cmd_INTERNAL: call 309 Cmd 37 response 01
    366:send_cmd_INTERNAL: call 415 Cmd 29 response 00
    419:mmc_disk_initialize: Checking CCS bit in OCR
    366:send_cmd_INTERNAL: call 420 Cmd 3A response 00
    423:mmc_disk_initialize: CMD58 response 80FF8000
    452:mmc_disk_initialize: Init okay
    40:disk_initialize: status = 0
    58:disk_read_INTERNAL: Call from 27
    366:send_cmd_INTERNAL: call 494 Cmd 11 response 00
    60:disk_read_INTERNAL: buf=20001588 sector=0 count=1
    27:test_task1: Read result 0
    28:test_task1: dump len 512
    FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF
    FE000000000000000000000000000000
    00000000000000000000000000000000
    00000000000000000000000000000000
    00000000000000000000000000000000
    00000000000000000000000000000000
    00000000000000000000000000000000
    00000000000000000000000000000000
    00000000000000000000000000000000
    00000000000000000000000000000000
    00000000000000000000000000000000
    00000000000000000000000000000000
    00000000000000000000000000000000
    00000000000000000000000000000000
    00000000000000000000000000000000
    00000000000000000000000000000000
    00000000000000000000000000000000
    00000000000000000000000000000000
    00000000000000000000000000000000
    00000000000000000000000000000000
    00000000000000000000000000000000
    00000000000000000000000000000000
    00000000000000000000000000000000
    00000000000000000000000000000000
    00000000000000000000000000000000
    00000000000000000000000000000000
    00000000000000000000000000000000
    00000000000000000000000000000000
    0000000000000000001B3DAFBF000080
    0101008311F4FD3E000000C2EF3A0000
    00000000000000000000000000000000
    00000000000000000000000000000000
  • My debug data is 100% consistent with logic analyzer traffic.
  • Initialization is the same as in FatFS reference driver, only SPI layer is changed, so I would expect the initialization to fail if something was wrong with SPI itself
  • SPI clock is around 150kHz
  • Card returns the same junk every time, another card returns another junk reliably
  • I am sending 2 dummy bytes with CS high between commands

What should I check/change to make read command work reliably?

Best Answer

What you read om the µC is the MBR (Master Boot Record) with the partition table. This data you cannot read on a OS like windows without admin privileges! The USB card reader data clearly shows the first sector of the "drive" (partiton)- which is not sector 0 (zero).

Some hex editors can show your the MBR if started as an admin - but you must use the correct physical device, which has no drive letter.

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