Mmc Block Length Register (Mmc_Blen) - Texas Instruments OMAP5910 Technical Reference Manual

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MMC/SD Host Controller

Table 7–107. MMC Block Length Register (MMC_BLEN)

Block Length (BLEN)

This register configures the core for the number of bytes to read or write. It

must be initialized at least once prior to starting an MMC, SD, or SPI block data

transfer (read or write).

Block length value

General operation: A write into this register (bits 10-0) initializes an 11-bit

counter that decrements by 1 after each byte transferred. A read into this regis-

ter returns the number of bytes remaining to be transferred. When the counter

reaches 0 and after the last byte transfer completes, BLEN is automatically

reloaded to its programmed value by the core.

In MMC/SD mode, this 11-bit value specifies the data block length. This value

must be set respectively with max 2

WRITE_BL_LEN

READ_BL_LEN and WRITE_BL_LEN are CSD register settings of the card

returned in a response, R2, following a SEND_CSD command (CMD9).

In SPI modes and for a read transaction, BLEN must be initialized with the

exact byte count to read negative 1, excluding the op-code and address

Op-code and address arguments that are passed to the SPI device must be

written into the FIFO buffer prior to starting the SPI transfer. BLEN starts to

decrement as soon as the buffer contents have been shifted out to the SPI

device. The buffer then starts to be filled with the received data from the SPI

In SPI modes and for a write transaction, BLEN must be initialized with the

exact byte count to write negative 1, including the number of bytes needed to

pass the op-code and address arguments.

It is recommended to have op-code and addresses that are passed to the SPI

module written into the FIFO buffer prior to starting the SPI transfer. This allows

in DMA write operation to access only the data portion. BLEN starts to

decrement for every byte shifted out to the SPI device.

0x000: 1 byte

0x7FF: 2048 bytes

Values after reset are low (all 11 bits).

-1 for a block write.

-1 for a block read or