UM10503
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© NXP B.V. 2012. All rights reserved.
User manual
Rev. 1.3 — 6 July 2012
459 of 1269
NXP Semiconductors
UM10503
Chapter 20: LPC43xx SD/MMC interface
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CRC Error on Command - If a CRC error is detected for a command, the CE-ATA
device does not send a response, and a response time-out is expected from the
Module. The ATA layer is notified that an MMC transport layer error occurred.
•
Write operation - Any MMC Transport layer error known to the device causes an
outstanding ATA command to be terminated. The ERR bits are set in the ATA status
registers and the appropriate error code is sent to the ATA Error register.
•
If nIEN=0, then the Command Completion Signal (CCS) is sent to the cpu.
If device interrupts are not enabled (nIEN=1), then the device completes the entire Data
Unit Count if the cpu controller does not abort the ongoing transfer.
During a multiple-block data transfer, if a negative CRC status is received from the device,
the data path signals a data CRC error to the BIU by setting the data CRC error bit in the
RINTSTS register. It then continues further data transmission until all the bytes are
transmitted.
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Read operation - If MMC transport layer errors are detected by the cpu controller, the
cpu completes the ATA command with an error status.
The cpu controller can issue a Command Completion Signal Disable (CCSD) followed by
a STOP TRANSMISSION (CMD12) to abort the read transfer. The cpu can also transfer
the entire Data Unit Count bytes without aborting the data transfer.
20.7.6 DMA descriptors
The SD/MMC DMA controller uses the following descriptor structures:
•
Dual-Buffer Structure – The distance between two descriptors is determined by the
Skip Length value programmed in the Descriptor Skip Length (DSL) field of the Bus
Mode Register (BMOD).
•
Chain Structure – Each descriptor points to a unique buffer and the next descriptor.
Fig 46. Dual-buffer descriptor structure
Descriptor A
Data Buffer 1
Data Buffer 2
Descriptor C
Data Buffer 1
Data Buffer 2
Descriptor B
Data Buffer 1
Data Buffer 2