ARM926EJ datasheet(92/236 Pages) ETC2

92 / 236 page

Memory Management Unit

3-28

ARM DDI 0198E

3.6

External aborts

In addition to the MMU generated aborts, external aborts can be generated for certain

types of access that involve transfers over the AHB bus. These can be used to flag errors

on external memory accesses. However, not all accesses can be aborted in this way.

The following accesses can be externally aborted:

•

page walks

•

noncached reads

•

nonbuffered writes

•

noncached read-lock-write (SWP) sequence.

For a read-lock-write (SWP) sequence, if the read externally aborts, the write is always

attempted.

A swap to an NCB region is forced to have precisely the same behavior as a swap to an

NCNB region. This means that the write part of a swap to an NCB region can be

externally aborted.

3.6.1

Enabling the MMU

Before enabling the MMU using CP15 c1 you must:

Program the TTB register (CP15 c2) and the domain access control register

(CP15 c3).

Program first-level and second-level page tables as required, ensuring that a valid

translation table is placed in memory at the location specified by the TTB register.

When these steps have been performed, you can enable the MMU by setting CP15 c1

bit 0 HIGH.

Care must be taken if the translated address differs from the untranslated address

because several instructions following the enabling of the MMU might have been

prefetched with the MMU off (VA = MVA = PA).

In this case, enabling the MMU can be considered as a branch with delayed execution.

A similar situation occurs when the MMU is disabled. Consider the following code

sequence:

MRC p15, 0, R1, c1, C0, 0

; Read control register

ORR R1, #0x1

; Set M bit

MCR p15, 0,R1,C1, C0,0

; Write control register and enable MMU

Fetch Flat

Fetch Translated

ARM926EJ bảng dữ liệu(PDF) 92 Page - List of Unclassifed Manufacturers

ARM926EJ bảng dữ liệu(HTML) 92 Page - List of Unclassifed Manufacturers

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

bảng dữ liệu tải về

Link URL