ARM編程中的ARM Boot 示例
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該程序對學習和理解arm編程很有幫助.為了便于理解,這里我全部采用實際地址,不用宏定義.
程序語言為 arm 匯編,具體過程參考arm編程,具體寄存器接口定義參見arm硬件手冊
VramBaseAddress EQU 0xC0000000 ;DRAM起始地址,在arm硬件地址映射定義,見arm編程
Length1 EQU 0x100
FlashBase EQU 0x70000000 ;Flash的基地址,在Boot模式下,為0x70000000
MMUCP CP 15 ;協處理器15
AREA |C$$code|, CODE, READONLY
ENTRY
EXPORT main
main
MOV r14, #0x70 ;設置MMU無效, 32位模式, Little endian
MCR MMUCP, 0, r14, c1, c0, 0
MRS r14, CPSR
BIC r14, r14, #0x1f ;Mask
ORR r14, r14, #0xc0 + 0x13 ;關閉所有 IRQ FIQ, 用SVC32 模式
MSR CPSR, r14
LDR r11, =0x80000000 ;內部寄存器基地址 0x80000000
LDR r12, =0x80001000
MOV r0, #0
STR r0, [r11, #0x280] ;disable 所有中斷
STR r0, [r12, #0x280]
LDR r0, =0x840100 ;在系統控制寄存器SYSCON1中
STR r0, [r11, #0x100] ;使能外部時鐘 EXCKEN 和串口 UART1
LDR r0, =0x06 ;在系統控制寄存器SYSCON2中
STR r0, [r12, #0x100] ;使能16-bit DRAM, 鍵盤KBD6
LDR r0, =0x03010100 ;在存儲控制寄存器MEMCFG1中
STR r0, [r11, #0x180] ;設置外設數據線寬度CS0:16位,CS1,2:32位,CS3:8位
;特別注意:
如設置線寬為16位,由于CPU是32位,CPU會把32位數據分兩次操作寫入,每次寫16位,這樣對32位的外設來說是一種浪費
例如: LDR r0, =0x10000000
LDR r1, =0x12345678
STR r1,[r0]
實際情況是 第一次寫入地址0x10000000的數據是 0x1234
第二次寫入地址0x10000002的數據是 0x5678示波器上觀察的情況是一個片選信號/CS低電平范圍內,有兩個寫入信號/WE低電平.
如設置線寬為32位,CPU會把32位數據一次寫入,如果外設是16位的話,如ISA網卡,就會造成高16位丟失.
例如: LDR r0, =0x10000000
LDR r1, =0x12345678
STR r1,[r0]
實際情況是 一次寫入地址0x10000000的數據是 0x12345678
LDR r0, = 0xff ;DRAM刷新率refresh rate,設置要適當,否則數據丟失
STR r0, [r11, #0x200]
LDR r13, =0xc0020000 ;設置堆棧 Stack, r13 為arm定義的堆棧指針
;Init OK
LDR r0, =receiving_msg
BL printmsg
BL dram_test ;跳轉指令,執行測試DRAM
LDR r0, =startloader_cmdmsg
BL printmsg
BL Beep
LDR r0, =0x60005 ;設置波特率 38400, 8位
LDR r11, =0x80000000
STR r0, [r11, #0x4c0] ;初始化串口 UART
;Receive data and save it to buffer ;開始接收數據
LDR r12, =SaveAddr ;First 8 bytes are start address and length
;Receive address
LDR r5, =0x4 ;Read first 4 bytes
MOV r0, #0
rx_loop1
LDR r1, [r11, #0x140] ;檢查系統狀態寄存器System Status Register 1
TST r1, #0x00400000 ;UART1 Rx 是否為空
BNE rx_loop1 ;等待數據 Wait data
LDR r1, [r11, #0x480] ;讀數據 Read data
AND r1, r1, #0xff
ORR r0, r1, r0, ROR #8
SUBS r5, r5, #1
BNE rx_loop1
MOV r0, r0, ROR #8
STR r0, [r12]
ADD r12, r12, #4
;Receive count
LDR r12, =Count
LDR r5, =0x4 ;Read second 4 bytes
MOV r0, #0
rx_loop2
LDR r1, [r11, #0x140] ;檢查系統狀態寄存器System Status Register 1
TST r1, #0x00400000 ;UART1 Rx 是否為空
BNE rx_loop2 ;等待數據 Wait data
LDR r1, [r11, #0x480] ;讀數據 Read data
AND r1, r1, #0xff
ORR r0, r1, r0, ROR #8
SUBS r5, r5, #1
BNE rx_loop2
MOV r0, r0, ROR #8
STR r0, [r12]
MOV r6, r0 ;Save the count to r6
;Receive data
MOV r5, r0
MOV r9, #0
LDR r10, =BufferBase
MOV r12, #0
rx_loop3
LDR r1, [r11, #0x140] ;System Status Register 1
TST r1, #0x00400000 ;UART1 Rx Empty
BNE rx_loop3 ;Wait data
LDR r1, [r11, #0x480] ;Read data
AND r1, r1, #0xff
STRB r1, [r10, r12]
ADD r12, r12, #1
nextbyte ;讀下一個字節
SUBS r5, r5, #1
BNE rx_loop3
;Receive data OK ;數據接收完畢
MOV r1, #0x31
BL send_char
MOV r1, #0x0d
BL send_char
MOV r1, #0x0a
BL send_char
;Save it to Flash ROM 把數據寫入Flash ROM
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