Tcm Write Buffer - ARM ARM926EJ-S Technical Reference Manual

Tightly-Coupled Memory Interface
5.7

TCM write buffer

5-30
Each TCM interface has a two word entry write buffer. This is required to de-pipeline
the address and data values produced by the ARM9EJ-S core so that non-speculative
writes can be made to memory with SRAM characteristics peformed without
introducing stall cycles.
The ARM9EJ-S core read requests take priority over writes, and consequently TCM
transactions can be out of order with respect to instruction execution. If a read access
occurs to a location that also has a corresponding entry in the write-buffer, then data is
forwarded from the write-buffer. If it is necessary to ensure that all outstanding writes
have completed on the TCM interface then the CP15 drain write buffer instruction can
be used ( MCR p15, 0, Rd, c7, c10, 4
until all oustanding buffered writes (TCM and AHB) have been completed.
To guarantee that the TCM write buffers have been drained and that all outstanding
requests on the TCM interface have completed, a drain write buffer instruction must be
used prior to disabling either of the TCM regions.
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). This instruction does not complete execution
ARM DDI0198D