start.S解析10

《朱老师物联网大讲堂》学习笔记

学习地址：www.zhulaoshi.org

虚拟地址映射，

好比数组，

数组下标好比索引，数组内容好比表项，

一个ARM的段式映射中长度为1MB,因此需要4G/1MB = 4096个映射单元，即数组有4096个单元，

实际上，我们把4096分成了好几部分，用循环来处理，

/* form a first-level section entry */
.macro FL_SECTION_ENTRY base,ap,d,c,b
.word (\base << 20) | (\ap << 10) | \
(\d << 5) | (1<<4) | (\c << 3) | (\b << 2) | (1<<1)
.endm
.section .mmudata, "a"
.align 14
// the following alignment creates the mmu table at address 0x4000.
.globl mmu_table
mmu_table:
.set __base,0
// Access for iRAM
.rept 0x100
FL_SECTION_ENTRY __base,3,0,0,0
.set __base,__base+1
.endr

// Not Allowed
.rept 0x200 - 0x100
.word 0x00000000
.endr

.set __base,0x200
// should be accessed
.rept 0x600 - 0x200
FL_SECTION_ENTRY __base,3,0,1,1
.set __base,__base+1
.endr

.rept 0x800 - 0x600
.word 0x00000000
.endr

.set __base,0x800
// should be accessed
.rept 0xb00 - 0x800
FL_SECTION_ENTRY __base,3,0,0,0
.set __base,__base+1
.endr

/*	.rept 0xc00 - 0xb00
.word 0x00000000
.endr */

.set __base,0xB00
.rept 0xc00 - 0xb00
FL_SECTION_ENTRY __base,3,0,0,0
.set __base,__base+1
.endr

// 0xC000_0000鏄犲皠鍒?x2000_0000
.set __base,0x300
//.set __base,0x200
// 256MB for SDRAM with cacheable
.rept 0xD00 - 0xC00
FL_SECTION_ENTRY __base,3,0,1,1
.set __base,__base+1
.endr

// access is not allowed.
@.rept 0xD00 - 0xC80
@.word 0x00000000
@.endr

.set __base,0xD00
// 1:1 mapping for debugging with non-cacheable
.rept 0x1000 - 0xD00
FL_SECTION_ENTRY __base,3,0,0,0
.set __base,__base+1
.endr

#else	// CONFIG_MCP_AC, CONFIG_MCP_H, CONFIG_MCP_B

有待完善！