Digi NS9215 manual Section descriptor Format, Bits Section Coarse Fine Description

First-level descriptor bit assignments: Priority encoding of fault status

			WO R K I N G W I T H T H E C P U	. .
			MemoryManagement Unit (MMU)..
				.
Bits
Section	Coarse	Fine	Description
[31:20]	[31:10]	[31:12]	Forms the corresponding bits of the physical address.
[19:12]	----	---	SHOULD BE ZERO
[11:10]	---	---	Access permission bits. See “Access permissions and
			domains” on page 106 and “Fault Address and Fault Status
			registers” on page 119 for information about interpreting
			the access permission bits.
9	9	[11:9]	SHOULD BE ZERO
[8:5]	[8:5]	[8:5]	Domain control bits
4	4	4	Must be 1.
[3:2]	---	---	Bits C and B indicate whether the area of memory mapped
			by this page is treated as write-back cachable, write-
			through cachable, noncached buffered, or noncached
			nonbuffered.
---	[3:2]	[3:2]	SHOULD BE ZERO
[1:0]	[1:0]	[1:0]	These bits indicate the page size and validity, and are
			interpreted as shown in “First-level descriptor bit
			assignments: Priority encoding of fault status” on
			page 111.

First-level descriptor bit assignments: Interpreting first level descriptor bits [1:0]

Value	Meaning	Description
0 0	Invalid	Generates a section translation fault.
0 1	Coarse page table	Indicates that this is a coarse page table descriptor.
1 0	Section	Indicates that this is a section descriptor.
1 1	Fine page table	Indicates that this is a fine page table descriptor.

Section descriptor A section descriptor provides the base address of a 1 MB block of memory.

Section descriptor

format	31	20	19	12	11	10	9	8	5	4	3	2	1	0
	Section base address		SBZ		AP		S	Domain		1	C	B	1	0
							B
							Z

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