AN4253 datasheet(30/44 Pages) STMICROELECTRONICS

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RAM initialization

AN4253

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DocID024255 Rev 2

RAM initialization

Figure 14. Flow of the "RAM initialization" phase

An Important part of the startup code is linked to RAM initialization. Especially in case of

destructive resets when the content of the RAM cells, data plus ECC syndrome bits, are

undefined. In such case the entire RAM memory or at least all used sections must be

initialized to update ECC syndrome bits. Not doing this can lead to multiple bit ECC faults

during any read operation or byte, half word write operation.

Default reset state

8.1

Init whole RAM

There are mainly two ways how to initialize the RAM. Both need supportive information from

linker file.

•

Using multiple word store instructions e_stmw, that store set of GPRs registers in

consecutive order

•

Using standard 32 bit store instructions e_stwu

This part of startup code can be used for initializing the RAM memory to specific value, i.e.

zero.

8.1.1

Code sequence

Determine number of cycles to execute in multiples of words. It depends on type of

instructions.

Place iteration count to core counter register

Prepare start address and adjust it if e_stwu instruction will be used

Prepare value to write. In case of e_stmw instruction, the value must be written to all

involved GPRs

Issue store instruction

Decrement counter and jump for next store cycle if not zero

•

Destructive reset

RAM undefined. It is needed to initialize it completely.

•

Functional reset

RAM preserves its content. It can be used as non-volatile storage.

AN4253 Datasheet(PDF) 30 Page - STMicroelectronics