CL-PS7500FE 查看數據表（PDF） - Cirrus Logic

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CL-PS7500FE

System-on-a Chip for Internet Appliance

Cirrus Logic 

CL-PS7500FE

System-on-a-Chip for Internet Appliance

6.10.2 Translation Fault

There are two types of Translation fault:

q Section is generated if the Level One descriptor is marked as invalid. This happens if bits 1:0 of the descriptor

are both ‘0’ or both ‘1’.

q Page is generated if the Page Table entry is marked as invalid. This happens if bits 1:0 of the entry are both

‘0’ or both ‘1’.

6.10.3 Domain Fault

There are two types of Domain fault:

q Section

q Page

In both cases the Level One descriptor holds the 4-bit Domain field that selects one of the sixteen 2-bit

domains in the Domain Access Control register. The two bits of the specified domain are then checked

for access permissions as detailed in Table 6-2 on page 42. For a Section fault, the domain is checked

once the Level One descriptor is returned. For a Page fault, the domain is checked once the Page Table

entry is returned.

If the specified access is either ‘no access’ (‘00’) or ‘reserved’ (‘10’), then either a Section Domain or Page

Domain fault occurs.

6.10.4 Permission Fault

There are two types of Permission fault:

q Section

q Subpage

Permission faults are checked at the same time as Domain faults. If the 2-bit domain field returns Client

(01), then the permission access check is invoked as follows:

1) Section

If the Level One descriptor defines a section-mapped access, then the AP bits of the descriptor define whether

or not the access is allowed according to Table 6-2. Their interpretation is dependent upon the setting of the S

bit (Control register, bit 8). If the access is not allowed, a Section Permission fault is generated.

2) Subpage

If the Level One descriptor defines a page-mapped access, then the Level Two descriptor specifies four access

permission fields (AP3–AP0) each corresponding to one quarter of the page. For small pages, AP3 is selected

by the top 1 Kbyte of the page, and AP0 is selected by the bottom 1 Kbyte of the page; for large pages, AP3 is

selected by the top 16 Kbytes of the page, and AP0 is selected by the bottom 16 Kbyte of the page. The selected

AP bits are then interpreted in exactly the same way as for a section (see Table 6-2), the only difference is that

the fault generated is a Subpage Permission fault.

6.11 External Aborts

The CL-PS7500FE does not support external aborts.

50

ARM PROCESSOR MMU

ADVANCE DATA BOOK v2.0

June 1997

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