AN3307 datasheet(25/37 Pages) STMICROELECTRONICS

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AN3307

Class B solution structure

Doc ID 18186 Rev 4

25/37

5.2.3

Flash complete checksum self-test

The CRC checksum computation is performed on the entire Flash space defined in the

linker checksum structure. The result of the computation is compared with that of the linker.

If they differ, the test fails. Refer to Section 4.3.3: Debugging the package for additional

comments on CRC procedures.

Figure 9.

Flash startup self-test structure

5.2.4

Full RAM March C-/X self-test

The entire RAM space is alternately checked and filled word by word with background

patterns (value 0x00000000) and inverse background patterns (value 0xFFFFFFFF) in six

loops as shown in Figure 10. The first three loops are performed in incremental order of

addresses, and the last three in decremented reverse order. The order of tested addresses

is scrambled as it respects the physical order of addresses to prevent and recognize any

cross-talk between physically adjacent memory cells. The scramble principle is shown in

Table 3. The basic physical unit is a pattern (a row) covering a block of 16 words. The

numbers in the table cells represent logical addresses, while their order in the table

represents the physical layout. Bold frames highlight the places where the logical order is

scrambled. Any address scrambling is not present at new ST products. The March test of

RAM is simplified significantly for them.

Some new products have implemented hardware word protection with single bit redundancy

(hardware parity check) applied on CCM RAM or on part of SRAM at least. The applied

software SRAM March test can be removed completely or partially from both startup and

runtime test sets for this case. The software test can be used only for testing of those parts

of RAM which are not covered by the hardware parity check or as a supplementary testing

method.

Table 3.

Physical order of RAM addresses organized into blocks of 16 words

Fail Safe() routine

Test OK

16-bit CRC =

_check sum

Yes

Compute 16-bit CRC check sum

AI18007

Physical order of addresses---->

...

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