CE5.0 - eboot匯編Startup.s中MMU設置流程詳細分析??
以下為SMDK開發板startup.s部分啟動代碼.??
;-------------------------------------------------------------------------------??
MemoryMap EQU 0x2a4??
BANK_SIZE EQU 0x00100000 ; 1MB per bank in MemoryMap array??
BANK_SHIFT EQU 20??
?
; Define RAM space for the Page Tables:??
;??
PHYBASE EQU 0x30000000 ; physical start??
PTs EQU 0x30010000 ; 1st level page table address (PHYBASE + 0x10000)??
??????????????????????????????????????? ; save room for interrupt vectors.??
;------------------------------------------------------------------------------??
; Copy boot loader to memory??
??????? ands r9, pc, #0xFF000000 ; see if we are in flash or in ram??
//如果高8字節非0,那么說明pc已經在ram,否則說明現在pc位于reset之后的0x00000000地址區間[luther.gliethttp]??
??????? bne %f20 ; go ahead if we are already in ram//高8字節非0,說明eboot已在DDR中,跳到下面的20標號??
?
??????? ; This is the loop that perform copying.??
??????? ldr r0, = 0x38000 ; offset into the RAM???
??????? add r0, r0, #PHYBASE ; add physical base //eboot最終的物理地址為0x30038000,這也就是PLATFORM/SMDK2440A/Src/Bootloader/Eboot_usb/boot.bib中定義的??
//eboot鏈接地址EBOOT 8c038000 00016800 RAMIMAGE //一個.bib允許由一個RAMIMAGE類型段,生成一個對應的.bin文件,之后由romimage.exe生成.nb0同時填充eboot的pTOC全局變量指針[luther.gliethttp]??
??????? mov r1, r0 ; (r1) copy destination??
//因為s3c2440在nand啟動時,會將nand中前4k數據讀取到s3c2440內部的4k ram中,同時ram映射成0地址,cpu??
//跳轉到ram開始執行從nand讀取的前4k代碼數據,于是讀取位于ram中0地址之后的4k數據就等同于讀取了nand的前4k數據[luther.gliethttp].??
??????? ldr r2, =0x0 ; (r2) flash started at physical address 0??
??????? ldr r3, =0x10000 ; counter (0x40000/4)//循環讀取4k字節??
10 ldr r4, [r2], #4??
??????? str r4, [r1], #4??
??????? subs r3, r3, #1??
??????? bne %b10??
??????? ; Restart from the RAM position after copying.??
??????? mov pc, r0 //跳轉到物理地址0x30038000重新執行上面的reset代碼,再次執行時因為已經位于ram,所以將執行上面的bne %f20語句[luther.gliethttp]??
??????? nop //為流水線添加可能存在的指令最大空取次數??
??????? nop??
??????? nop??
??????? ; Shouldn't get here.??
??????? b?????? .??
??????? INCLUDE oemaddrtab_cfg.inc? //這就是eboot的mmu映射表,位于PLATFORM/SMDK2440A/Src/Inc/oemaddrtab_cfg.inc??
/*?
??????? EXPORT? g_oalAddressTable[DATA]?
g_oalAddressTable?
??????? DCD???? 0x80000000, 0x32000000, 32????? ; 32 MB DRAM BANK 6?
??????? DCD???? 0x82000000, 0x08000000, 32????? ; 32 MB SROM(SRAM/ROM) BANK 1?
??????? DCD???? 0x84000000, 0x10000000, 32????? ; nGCS2: PCMCIA/PCCARD?
??????? DCD???? 0x86000000, 0x18000000, 32????? ; 32 MB SROM(SRAM/ROM) BANK 3?
??????? DCD???? 0x88000000, 0x20000000, 32????? ; 32 MB SROM(SRAM/ROM) BANK 4?
??????? DCD???? 0x8A000000, 0x28000000, 32????? ; 32 MB SROM(SRAM/ROM) BANK 5?
??????? DCD???? 0x8C000000, 0x30000000, 32????? ; 32 MB DRAM BANK 6?
??????? DCD???? 0x90800000, 0x48000000,? 1????? ; Memory control register?
??????? DCD???? 0x90900000, 0x49000000,? 1????? ; USB Host register?
??????? DCD???? 0x90A00000, 0x4A000000,? 1????? ; Interrupt Control register?
??????? DCD???? 0x90B00000, 0x4B000000,? 1????? ; DMA control register?
??????? DCD???? 0x90C00000, 0x4C000000,? 1????? ; Clock & Power register?
??????? DCD???? 0x90D00000, 0x4D000000,? 1????? ; LCD control register?
??????? DCD???? 0x90E00000, 0x4E000000,? 1????? ; NAND flash control register?
??????? DCD???? 0x90F00000, 0x4F000000,? 1????? ; Camera control register?
??????? DCD???? 0x91000000, 0x50000000,? 1????? ; UART control register?
??????? DCD???? 0x91100000, 0x51000000,? 1????? ; PWM timer register?
??????? DCD???? 0x91200000, 0x52000000,? 1????? ; USB device register?
??????? DCD???? 0x91300000, 0x53000000,? 1????? ; Watchdog Timer register?
??????? DCD???? 0x91400000, 0x54000000,? 1????? ; IIC control register?
??????? DCD???? 0x91500000, 0x55000000,? 1????? ; IIS control register?
??????? DCD???? 0x91600000, 0x56000000,? 1????? ; I/O Port register?
??????? DCD???? 0x91700000, 0x57000000,? 1????? ; RTC control register?
??????? DCD???? 0x91800000, 0x58000000,? 1????? ; A/D convert register?
??????? DCD???? 0x91900000, 0x59000000,? 1????? ; SPI register?
??????? DCD???? 0x91A00000, 0x5A000000,? 1????? ; SD Interface register?
??????? DCD???? 0x92000000, 0x00000000, 32????? ; 32 MB SROM(SRAM/ROM) BANK 0?
??????? DCD???? 0x00000000, 0x00000000,? 0????? ; end of table?
*/???
??????? ; Compute physical address of the OEMAddressTable.??
20????? add???? r11, pc, #g_oalAddressTable - (. + 8)??
??????? ldr???? r10, =PTs??????????????? ; (r10) = 1st level page table??
0x20000000??
??????? ; Setup 1st level page table (using section descriptor)???????
??????? ; Fill in first level page table entries to create "un-mapped" regions??
??????? ; from the contents of the MemoryMap array.??
??????? ;??
??????? ;?? (r10) = 1st level page table??
??????? ;?? (r11) = ptr to MemoryMap array??
//PTR的地址大家都選在了DDR開始的offset處,ce為64k偏移,linux也是這樣做的??
//然后第1級MMU入口為pc地址的高14位(過濾掉低18位)[luther.gliethttp]??
//比如0x80000000地址對應的第1級MMU入口偏移為0x80000000 >> 18 = 0x2000??
??????? add???? r10, r10, #0x2000?????? ; (r10) = ptr to 1st PTE for "unmapped space"?
//r10存放0x80000000虛擬地址在PTR中的對應地址??
??????? mov???? r0, #0x0E?????????????? ; (r0) = PTE for 0: 1MB cachable bufferable //有高速緩存C和寫緩沖B??
??????? orr???? r0, r0, #0x400????????? ; set kernel r/w permission??
25????? mov???? r1, r11???????????????? ; (r1) = ptr to MemoryMap array??
??????????
30????? ldr???? r2, [r1], #4??????????? ; (r2) = virtual address to map Bank at??
??????? ldr???? r3, [r1], #4??????????? ; (r3) = physical address to map from??
??????? ldr???? r4, [r1], #4??????????? ; (r4) = num MB to map??
??????? cmp???? r4, #0????????????????? ; End of table???
??????? beq???? %f40??? //表示cachable地址0x80000000~0xa0000000映射MMU創建完畢,表結尾,前跳到40標號,創建對應的uncached映射MMU[luther.gliethttp]??
??????? ldr???? r5, =0x1FF00000??
??????? and???? r2, r2, r5????????????? ; VA needs 512MB, 1MB aligned.? //對va虛擬地址進行512M對齊[luther.gliethttp]??
//也就是r2的上限值不能超過0x20000000即512M,因為r10現在指向1級映射表的0x80000000虛擬地址,??
//又因為0x80000000+0x20000000=0xa0000000開始地址存放的是uncached地址,所以這里要做512M數據限制[luther.gliethttp]??
??????? ldr???? r5, =0xFFF00000??
??????? and???? r3, r3, r5????????????? ; PA needs 4GB, 1MB aligned.??? //對pa物理地址進行4G對齊??
??????? add???? r2, r10, r2, LSR #18??
??????? add???? r0, r0, r3????????????? ; (r0) = PTE for next physical page //在MMU控制flag基礎上追加映射到的pa物理地址[luther.gliethttp]??
35????? str???? r0, [r2], #4??????????? //存到r2對應的PTR偏移中??
??????? add???? r0, r0, #0x00100000???? ; (r0) = PTE for next physical page //1M遞增,因為1<<18=256K,而每一個pte描述4k頁,所以最終描述256k*4k=1M地址空間[luther.gliethttp]??
??????? sub???? r4, r4, #1????????????? ; Decrement number of MB left???
??????? cmp???? r4, #0??
??????? bne???? %b35??????????????????? ; Map next MB?? //遍歷到該region結束??
??????? bic???? r0, r0, #0xF0000000???? ; Clear Section Base Address Field??
??????? bic???? r0, r0, #0x0FF00000???? ; Clear Section Base Address Field//清空r0中的地址信息[lutehr.gliethttp]??
??????? b?????? %b30??????????????????? ; Get next element? //繼續創建oemaddrtab_cfg.inc描述的下一region[luther.gliethttp]??
//創建對應的0xa0000000開始的uncached映射MMU表???
40????? tst???? r0, #8????????
//比較C高速緩存是否仍然置位,如果仍然置位了,那么說明還沒有執行uncached創建,如果C位已經清0,那么說明,uncached循環也執行完畢了,所以跳回到25標號繼續創建[luther.gliethttp]??
??????? bic???? r0, r0, #0x0C?????????? ; clear cachable & bufferable bits in PTE//清除B寫緩沖和C高速緩存[luther.gliethttp]??
??????? add???? r10, r10, #0x0800?????? ; (r10) = ptr to 1st PTE for "unmapped uncached space"//r10現在對應0x80000000虛擬地址的PTR起始地址,hex(0x20000000>>18)為0x800,??
//所以r10 = r10 + 0x800;之后r10指向了0xa0000000虛擬地址對應的PTR起始地址[luther.gliethtp]??
??????? bne???? %b25??????????????????? ; go setup PTEs for uncached space??
//ok,現在0x80000000 cachable空間和0xa0000000 uncached空間都已經創建完畢了[luther.gliethttp]??
??????? sub???? r10, r10, #0x3000?????? ; (r10) = restore address of 1st level page table//該句好像有問題,不過還好后面用到r10之前,又對r10進行了重新賦值,所以也更說明,該句操作無意義[luther.gliethttp]??
//接下來為虛擬0地址建立cachable和uncached映射[lutehr.gliethttp]??
??????? ; Setup mmu to map (VA == 0) to (PA == 0x30000000).??
??????? ldr???? r0, =PTs??????????????? ; PTE entry for VA = 0??
??????? ldr???? r1, =0x3000040E???????? ; uncache/unbuffer/rw, PA base == 0x30000000//以C,B均開啟的方式映射虛擬地址0到pa物理地址0x30000000??
??????? str???? r1, [r0]??
??????? ; uncached area.??
??????? add???? r0, r0, #0x0800???????? ; PTE entry for VA = 0x0200.0000 , uncached//接下來的0x2000000虛擬地址被映射為虛擬0地址的uncached起始地址[luther.gliethttp]??
??????? ldr???? r1, =0x30000402???????? ; uncache/unbuffer/rw, base == 0x30000000//以C,B均不開啟的方式映射虛擬地址0到pa物理地址0x30000000??
??????? str???? r1, [r0]??
//經過上面設置可以看到??
//虛擬地址0對應0x30000000的cachable??
//虛擬地址0x2000000對應0x30000000的uncached.[luther.gliethttp]??
??????? ; Comment:??
??????? ; The following loop is to direct map RAM VA == PA. i.e.???
??????? ;?? VA == 0x30XXXXXX => PA == 0x30XXXXXX for S3C2400??
??????? ; Fill in 8 entries to have a direct mapping for DRAM??
??????? ;??
??????? ldr???? r10, =PTs?????????????? ; restore address of 1st level page table??
??????? ldr???? r0,? =PHYBASE?????????? //PHYBASE為0x30000000,將虛擬地址映射到相同的物理地址??
??????? add???? r10, r10, #(0x3000 / 4) ; (r10) = ptr to 1st PTE for 0x30000000 //就是(0x30000000 >> 16) >> 2即(0x30000000 >> 16) / 4 [luther.gliethttp]??
//現在r10指向了和DDR地址相等的PA地址對應的PTR地址處??
??????? add???? r0, r0, #0x1E?????????? ; 1MB cachable bufferable??
??????? orr???? r0, r0, #0x400????????? ; set kernel r/w permission??
??????? mov???? r1, #0???
??????? mov???? r3, #64???????????????? //映射64M空間,因為我們的物理DDR只有64M(見上面的oemaddrtab_cfg.inc表圖),不能大于512,因為下面只支持到512次循環(r1為循環次數,每循環1次,創建1M空間映射表)[luther.gliethtp]??
45????? mov???? r2, r1????????????????? ; (r2) = virtual address to map Bank at??
??????? cmp???? r2, #0x20000000:SHR:BANK_SHIFT? //0x20000000>>20=512M,??
??????? add???? r2, r10, r2, LSL #BANK_SHIFT-18 //add r2, r10, r2, 4即r2 = r10 + r2*4;正好為PTR操作時的4字節對齊邊界[luther.gliethttp]??
??????? strlo?? r0, [r2]??????????????????????? //如果還沒有操作到512M,那么填充PTR,如果現在映射操作已經操作過了512M大小,那么忽略??
??????? add???? r0, r0, #0x00100000???? ; (r0) = PTE for next physical page??
??????? subs??? r3, r3, #1??
??????? add???? r1, r1, #1??
??????? bgt???? %b45??
??????? ldr???? r10, =PTs?????????????? ; (r10) = restore address of 1st level page table??
??????? ; The page tables and exception vectors are setup.??
??????? ; Initialize the MMU and turn it on.??
??????? mov???? r1, #1??
??????? mcr???? p15, 0, r1, c3, c0, 0?? ; setup access to domain 0??
??????? mcr???? p15, 0, r10, c2, c0, 0??
??????? mcr???? p15, 0, r0, c8, c7, 0?? ; flush I+D TLBs??? //flush所有MMU相關空間??
??????? mov???? r1, #0x0071???????????? ; Enable: MMU?????? //設置打開MMU標志到r1??
??????? orr???? r1, r1, #0x0004???????? ; Enable the cache? //設置打開cache標志到r1??
??????? ldr???? r0, =VirtualStart?????? //取出VirtualStart編譯期間得到的虛擬地址值,在0x30038000~0x30038000+eboot_size之間[luther.gliethtp]??
??????? cmp???? r0, #0????????????????? ; make sure no stall on "mov pc,r0" below //執行該比較,使r0踏實的讀入VirtualStart數值??
??????? mcr???? p15, 0, r1, c1, c0, 0?? //將MMU設置標志寫入p15協處理器,生效設置[luther.gliethttp]??
??????? mov???? pc, r0????????????????? ;? & jump to new virtual address //跳轉過去,此刻之后MMU已經打開,所有允許操作的虛擬地址都在PLATFORM/SMDK2440A/Src/Inc/oemaddrtab_cfg.inc中定義[luther.gliethttp]??
??????? nop??
??????? ; MMU & caches now enabled.??
??????? ;?? (r10) = physcial address of 1st level page table??
??????? ;??
VirtualStart??
??????? mov???? sp, #0x8C000000???????? //設置?？臻g,從這里來看,sp棧頂對應的DDR物理地址為0x30030000,然后向下生長,從boot.bib中??
/*?
MEMORY?
;?? Name???? Start???? Size????? Type?
;?? -------? --------? --------? ----?
??? ARGS???? 8c020800? 00000800? RESERVED?
??? BINFS??? 8c021000? 00005000? RESERVED?
??? RAM????? 8c026000? 00006000? RAM?????
??? STACK??? 8c02c000? 00004000? RESERVED? //0x2c000+0x4000=0x30000 保留該16K地址空間用作eboot的sp?？臻g?
??? EBOOT??? 8c038000? 00016800? RAMIMAGE?
*/?
可以看到sp?？臻g由.bib保留,位于0x30030000~0x3002c000,棧sp從0x30030000開始向下生長[luther.gliethttp]??
??????? add???? sp, sp, #0x30000??????? ; arbitrary initial super-page stack pointer??
??????? b?????? main //跳轉到main主函數,?

本文來自CSDN博客，轉載請標明出處：http://blog.csdn.net/UN_ChairMan/archive/2010/12/16/6081151.aspx

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