Electronic – Need help with SD Card Initialization (CLK Syncronization)

sdspi

EDIT 1 : I made changes to the code as @Anonymous suggested in the answer. It seems to have improved but now I seems to be getting incorrect response OR SD CARD putting response at the wrong time.

The logic data file after making changes as Anonymous suggested in the answer

I am trying to bitbang SPI interface for the sd card. I was at first confused regarding the mode to be used. so I asked regarding the SPI Mode over here.

I am initializing my CLK as Output with internal pull up and driving low. Same goes for the MOSI. while MISO is Input , Pull up and nothing driving that.

Here is my SPI Send and Recieve.

int spi_bb_send(spi_bb_config_t *spi_conf,unsigned char data)
{
  int i;
  uint8_t data_in = 0;

  // send bits 7..0
  for (i = 0; i < 8; i++)
  {
      spi_pin_clear(&(spi_conf->clk));

      // consider leftmost bit
      // set line high if bit is 1, low if bit is 0
      if (data & (1<<7))
          spi_pin_set(&(spi_conf->mosi));
      else
          spi_pin_clear(&(spi_conf->mosi));

       data_in <<= 1;
      data_in |= gpio_read(&(spi_conf->miso));

      Delay(SPI_TIME_IN_US(SPI_FREQ_KHZ));

      // pulse clock to indicate that bit value should be read
      spi_pin_set(&(spi_conf->clk));
      Delay(SPI_TIME_IN_US(SPI_FREQ_KHZ));

      //read the miso
      //data_in |= gpio_read(&(spi_conf->miso));

      // shift byte left so next bit will be leftmost
      data <<= 1;       
  }

  Delay(SPI_TIME_IN_US(SPI_FREQ_KHZ));
  spi_pin_clear(&(spi_conf->clk));

  return data_in;
}

int spi_bb_recieve(spi_bb_config_t *spi_conf)
{
    return(spi_bb_send(spi_conf,0xFF));
}

The initialization command have been tried as per Physical Layer document provided by SD ORD i.e following this initialization flow. initialization flow

As well as the initialization flow I found from this Answer regarding initialization flow.

The issue I am facing is I am getting the command and response for the 1st two commands correctly that is CMD0 and CMD8 and I am not facing any issue no matter how many times I try. When I send the third command i.e :

1) CMD58 as per the SD Org document , I dont get any response back.
2) CMD55 as per the person's answer on this SE, I seem to get correct response but the reponse I read get's an 0xF before the reponse so I believe that SD Card starts reponding from halfway of the clock generated. So I hooked up logic analyzer to it and here are the results.

Command 55 : Command 55

No Response on the first clock : No Response

Response : Response

There is some insights given on the link to answer pasted above that say :

Note that responses that have the MSB set but ain't 0xFF usually suggest that your SPI got a shift in clocking (as a result of e.g. Vcc drop, which happens routinely when you're doing SD hotplugs). To fix it, you can try to completely reset the device (power on/off, deassert/assert S̲S̲ etc.); it usually works.

But I am not doing any hotplug and neither resetting / power cycling works, So can anyone help? Please?

Best Answer

Your diagrams show chip select as always active. I do not say that it would not work this way, but deactivating CS, in most of the cases, signals card that host is finished with the command.

The I have the following suggestion for you - change the way you access the card:

  1. when powered on, you must clock CLK for some time (70 times or something like this) to enable card to initialize and synchronize;
  2. when you want to access the card, you have CS as high (inactive), and perform 8 spare clock cycles to the card. MOSI stays high;
  3. then you get CS low, and perform another 8 spare clock pulses with MOSI being high;
  4. starting next clock cycle you shift command into the sd-card. After command is shifted in, you wait for response as instructed in the documentation;
  5. after you have got required response, you do NOT deactivate CS, and perform 8 spare clocks with MOSI high;
  6. then you deactivate CS, and perform another 8 spare clocks with CS high and MOSI high.
  7. and then you are ready for next access.
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