Atmel SAM4S-XPLD Atmel ATSAM4S-XPLD ATSAM4S-XPLD Hoja De Datos

 824

SAM4S [DATASHEET]

11100E–ATARM–24-Jul-13

In boot operation mode, the processor can read boot data from the slave (MMC device) by keeping the CMD line low
after power-on before issuing CMD1. The data can be read from either the boot area or user area, depending on register
setting. As it is not possible to boot directly on SD-CARD, a preliminary boot code must be stored in internal Flash.

1.

Configure the HSMCI data bus width programming SDCBUS Field in the HSMCI_SDCR register. The 
BOOT_BUS_WIDTH field located in the device Extended CSD register must be set accordingly.

2.

Set the byte count to 512 bytes and the block count to the desired number of blocks, writing BLKLEN and BCNT 
fields of the HSMCI_BLKR Register.

3.

Issue the Boot Operation Request command by writing to the HSMCI_CMDR register with SPCMD field set to 
BOOTREQ, TRDIR set to READ and TRCMD set to “start data transfer”.

4.

The BOOT_ACK field located in the HSMCI_CMDR register must be set to one, if the BOOT_ACK field of the 
MMC device located in the Extended CSD register is set to one.

5.

Host processor can copy boot data sequentially as soon as the RXRDY flag is asserted.

6.

When Data transfer is completed, host processor shall terminate the boot stream by writing the HSMCI_CMDR 
register with SPCMD field set to BOOTEND.

The XFRDONE flag in the HSMCI_SR indicates exactly when the read or write sequence is finished.

CMD line

HSMCI read CMD

Card response

CMDRDY flag

Data

1st Block

Last Block

Not busy flag

XFRDONE flag

The CMDRDY flag is released 8 tbit  after the end of the card response.