RM48L952 datasheet(75/156 Pages) TI1

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RM48L952

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SPNS177

– SEPTEMBER 2011

4.9.4

POM Overlay Considerations

•

The POM overlay can map onto up to 8MB of the internal or external memory space. The starting

address and the size of the memory overlay are configurable via the POM module control registers.

Care must be taken to ensure that the overlay is mapped on to available memory.

•

ECC must be disabled by software via CP15 in case POM overlay is enabled; otherwise ECC errors

will be generated.

•

POM overlay must not be enabled when the flash and internal RAM memories are swapped via the

MEM SWAP field of the Bus Matrix Module Control Register 1 (BMMCR1).

•

When POM is used to overlay the flash on to internal or external RAM, there is a bus contention

possibility when another master accesses the TCM flash. This results in a system hang.

– The POM module implements a timeout feature to detect this exact scenario. The timeout needs to

be enabled whenever POM overlay is enabled.

– The timeout can be enabled by writing 1010 to the Enable TimeOut (ETO) field of the POM Global

Control register (POMGLBCTRL, address = 0xFFA04000).

– In case a read request by the POM cannot be completed within 32 HCLK cycles, the timeout (TO)

flag is set in the POM Flag register (POMFLG, address = 0xFFA0400C). Also, an abort is

generated to the CPU. This can be a prefetch abort for an instruction fetch or a data abort for a

data fetch.

– The prefetch- and data-abort handlers must be modified to check if the TO flag in the POM module

is set. If so, then the application can assume that the timeout is caused by a bus contention

between the POM transaction and another master accessing the same memory region. The abort

handlers need to clear the TO flag, so that any further aborts are not misinterpreted as having been

caused due to a timeout from the POM.

System Information and Electrical Specifications

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RM48L952 Datasheet(PDF) 75 Page - Texas Instruments