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AR# 47517

Zynq-7000 AP SoC, SMC - NAND with ECC might not Deassert CS between Data Transactions

Description

The NAND flash controller normally deasserts the chip select (CS) between data transfers and keeps the chip select asserted between a data transaction and a command operation. This protocol is compatible with most devices. In certain modes of operation, the controller might incorrectly believe that it is about to perform a command operation after a data operation, and the controller keeps the chip select asserted between two data transactions.

This is avoided when ECC is disabled. When ECC is enabled:

  • Use full commands for writes
  • Read the ECC codes between the reading of blocks

Solution

Impact:

Minor, refer to the Work-arounds.

Work-arounds:

  • Use the ECC block in full command mode for writes. Read ECC codes between blocks for reads.

  • If you are reading or writing more than one 512 byte block, ensure that the data crosses the 512 byte boundary in a single un-interrupted transaction.

Configurations Affected:

Systems that use NAND with ECC.

Device Revision(s) Affected:

All, no plan to fix. Refer to (Xilinx Answer 47916) Zynq-7000 AP SoC Silicon Revision Differences.

The SMC is designed to support NAND devices that require CS to be held low between data-phase accesses, as well as devices that do not have this requirement. To satisfy both types of memory, the ECC block will not de-assert CS after a block transfer has been completed if it is about to issue a command. However, in certain modes of operation (specifically when column-change commands are enabled and software is not reading ECC codes between blocks), SMC incorrectly assumes that it is about to perform an operation and cancels the request to de-assert the CS.

Impact Detail: Under the above mentioned conditions, CS will not be de-asserted. This could result in deadlock if data or code required to create the next transaction is stored through the same EBI.

AR# 47517
Date Created 05/23/2012
Last Updated 03/27/2013
Status Active
Type Design Advisory
Devices
  • Zynq-7000