External Memory Interface Handbook Volume 3: Reference Material: For UniPHY-based Device Families

ID 683841
Date 3/06/2023
Document Table of Contents Byte Writes

The memory controller performs a read-modify-write operation to ensure that the ECC data remains valid when a subset of the bits of a word is being written.

Byte writes with ECC enabled are executed as a read-modify-write. Typical operations only use a single entry in the timer bank pool. Controller ECC enabled sub-word writes use two entries. The first operation is a read and the second operation is a write. These two operations are transferred to the timer bank pool with an address dependency so that the write cannot be performed until the read data has returned. This approach ensures that any subsequent operations to the same address (from the same port) are executed after the write operation, because they are ordered on the row list after the write operation.

If an entire word is being written (but less than a full burst) and the DM pins are connected, no read is necessary and only that word is updated. If controller ECC is disabled, byte-writes have no performance impact.