mci.BusSpeed

#include <file_config.h>

typedef struct {
   ..
  BOOL (*BusSpeed) (
    U32 kbaud);       /* Bus speed in kilo-baud */
   ..
} const MCI_DRV;

The BusSpeed function sets the transfer speed on the MCI interface to the requested baud rate. When SD/MMC Memory Card is initialized, low speed transfer (400 kBit/s maximum) is used. When the Card initialization is complete, the high speed MCI data transfer is used.

The argument kbaud specifies the requested baud rate.

The BusSpeed function is in the MCI Driver. The prototype is defined in file_config.h. You have to customize the function in your own MCI driver.

• It is important to set the actual MCI speed equal to (or less than) the requested baud rate kbaud, but not higher than the requested baud rate. The error might happen due to the integer math used for the calculation of a divide factor.

The BusSpeed function returns a value of __TRUE if successful or a value of __FALSE if unsuccessful.

mci.BusMode, mci.BusWidth, mci.CheckMedia, mci.Command, mci.Delay, mci.Init, mci.ReadBlock, mci.SetDma, mci.UnInit, mci.WriteBlock

/* MCI Device Driver Control Block */
MCI_DRV mci0_drv = {
  Init,
  UnInit,
  Delay,
  BusMode,
  BusWidth,
  BusSpeed,
  Command,
  ReadBlock,
  WriteBlock,
  NULL,
  CheckMedia                          /* Can be NULL if not existing */
};

static BOOL BusSpeed (U32 kbaud) {
  /* Set a MCI clock speed to desired value. */
  U32 div;

  /* baud = MCLK / (2 x (div + 1)) */
  div = (__MCLK/2000 + kbaud - 1) / kbaud;
  if (div > 0)    div--;
  if (div > 0xFF) div = 0xFF;
  MCI_CLOCK = (MCI_CLOCK & ~0xFF) | 0x300 | div;
  return (__TRUE);
}