MCI UHS-I Signal Voltage Switch

Host-controller phases of the SD UHS-I signal-voltage switch. More...

Macros
#define	ARM_MCI_VOLTAGE_SWITCH_PREPARE   (0x00UL)
	Prepare the host before voltage switch command.
#define	ARM_MCI_VOLTAGE_SWITCH_APPLY   (0x01UL)
	Apply 1.8 V signaling after the voltage switch command.
#define	ARM_MCI_VOLTAGE_SWITCH_CLOCK_ON   (0x02UL)
	Start or confirm SD card bus clock.
#define	ARM_MCI_VOLTAGE_SWITCH_VERIFY   (0x03UL)
	Verify completion of the voltage switch.
#define	ARM_MCI_VOLTAGE_SWITCH_ABORT   (0x04UL)
	Abort a prepared or incomplete voltage switch.
#define	ARM_MCI_VOLTAGE_SWITCH_RESET   (0x05UL)
	Restore the host signaling path for card power-up.

Description

Host-controller phases of the SD UHS-I signal-voltage switch.

Call ARM_MCI_Control with control = ARM_MCI_UHS_VOLTAGE_SWITCH. Set arg to one of the phase codes below.

To perform a voltage switch, MCI controlling software must use this order:

1. PREPARE.
2. Send voltage switch command using ARM_MCI_SendCommand and wait for its completion.
3. APPLY.
4. Wait at least 5 ms.
5. CLOCK_ON.
6. Wait at least 1 ms.
7. VERIFY.

Example:

volatile uint32_t MCI_Events;
 
void MCI_SignalEvent_Callback (uint32_t event) {
  // Save current event
  MCI_Events |= event;
}
 
// Switch Signaling Voltage
void mci_switch_signaling_voltage(void) {
  int32_t status;
  uint32_t r1 = 0U;
 
  // Prepare host controller for signaling voltage switch
  if (MCIdrv->Control(ARM_MCI_UHS_VOLTAGE_SWITCH, ARM_MCI_VOLTAGE_SWITCH_PREPARE) != ARM_DRIVER_OK) {
    return;
  }
 
  // Clear previous events
  MCI_Events = 0;
 
  // Send voltage switch command
  status = MCIdrv->SendCommand(11, 0U, ARM_MCI_RESPONSE_SHORT|ARM_MCI_RESPONSE_CRC, &r1);
 
  if (status == ARM_DRIVER_OK) {
    // Wait for event
    while ((MCI_Events & ARM_MCI_EVENT_COMMAND_COMPLETE) == 0U);
 
    // Change the signaling voltage selection from 3.3V to 1.8V
    status = MCIdrv->Control(ARM_MCI_UHS_VOLTAGE_SWITCH, ARM_MCI_VOLTAGE_SWITCH_APPLY);
 
    if (status == ARM_DRIVER_OK) {
      // Wait for the signaling voltage to stabilize
      delay_ms(5);
 
      // Turn on the SD clock after the voltage switch
      status = MCIdrv->Control(ARM_MCI_UHS_VOLTAGE_SWITCH, ARM_MCI_VOLTAGE_SWITCH_CLOCK_ON);
 
      if (status == ARM_DRIVER_OK) {
        // Wait for the card to release the data lines
        delay_ms(1);
 
        // Verify the voltage switch after memory card releases data lines
        status = MCIdrv->Control(ARM_MCI_UHS_VOLTAGE_SWITCH, ARM_MCI_VOLTAGE_SWITCH_VERIFY);
 
        if (status == ARM_DRIVER_OK) {
          // Voltage switch successful
          return;
        }
      }
    }
  }
  // Failed to switch signaling voltage, abort procedure
  MCIdrv->Control(ARM_MCI_UHS_VOLTAGE_SWITCH, ARM_MCI_VOLTAGE_SWITCH_ABORT);
}

Macro Definition Documentation

ARM_MCI_VOLTAGE_SWITCH_PREPARE

#define ARM_MCI_VOLTAGE_SWITCH_PREPARE   (0x00UL)

Prepare the host before voltage switch command.

ARM_MCI_VOLTAGE_SWITCH_APPLY

#define ARM_MCI_VOLTAGE_SWITCH_APPLY   (0x01UL)

Apply 1.8 V signaling after the voltage switch command.

ARM_MCI_VOLTAGE_SWITCH_CLOCK_ON

#define ARM_MCI_VOLTAGE_SWITCH_CLOCK_ON   (0x02UL)

Start or confirm SD card bus clock.

ARM_MCI_VOLTAGE_SWITCH_VERIFY

#define ARM_MCI_VOLTAGE_SWITCH_VERIFY   (0x03UL)

Verify completion of the voltage switch.

ARM_MCI_VOLTAGE_SWITCH_ABORT

#define ARM_MCI_VOLTAGE_SWITCH_ABORT   (0x04UL)

Abort a prepared or incomplete voltage switch.

Stop the switch logic and leave the host interface electrically safe. Allow this operation after PREPARE, including after a failed phase.

ARM_MCI_VOLTAGE_SWITCH_RESET

#define ARM_MCI_VOLTAGE_SWITCH_RESET   (0x05UL)

Restore the host signaling path for card power-up.

Restore the host pads, voltage selection, and switch state for 3.3 V signaling. Call while card power is removed.