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550 1.0.9
check file extension

ROM:FFFF4F0C                 LDRB    R1, [R0,#-3]
ROM:FFFF4F10                 CMP     R1, #'F'
ROM:FFFF4F14                 BNE     loc_FFFF5058
ROM:FFFF4F18                 LDRB    R1, [R0,#-2]
ROM:FFFF4F1C                 CMP     R1, #'I'
ROM:FFFF4F20                 BNE     loc_FFFF5058
ROM:FFFF4F24                 LDRB    R0, [R0,#-1]
ROM:FFFF4F28                 CMP     R0, #'R'
ROM:FFFF4F2C                 BNE     loc_FFFF5058
ROM:FFFF4F30                 LDR     R4, =0x40800000 ; FIR file location
ROM:FFFF4F34                 LDR     R0, =0xF8002000
ROM:FFFF4F38                 LDR     R0, [R0,#0x14] ; update flag
ROM:FFFF4F3C                 CMN     R0, #1
ROM:FFFF4F40                 BNE     loc_FFFF4F48

check model id in FIR header

ROM:FFFF4F44                 MOV     R0, #0x270 ; 550d model number
ROM:FFFF4F48 loc_FFFF4F48                            
ROM:FFFF4F48                 LDR     R1, [R4]
ROM:FFFF4F4C                 ORR     R0, R0, #0x80000000
ROM:FFFF4F50                 CMP     R1, R0
ROM:FFFF4F54                 BEQ     loc_FFFF4F6C

compute and check checksum

ROM:FFFF4FBC loc_FFFF4FBC                            
ROM:FFFF4FBC                 CMP     R0, R3   ; r3 = size
ROM:FFFF4FC0                 BCS     loc_FFFF4FD8
ROM:FFFF4FC4                 LDR     R12, =0x40800000
ROM:FFFF4FC8                 LDRB    R12, [R12,R0]
ROM:FFFF4FCC                 ADD     R2, R2, R12
ROM:FFFF4FD0                 ADD     R0, R0, #1
ROM:FFFF4FD4                 B       loc_FFFF4FBC
ROM:FFFF4FD8 ; ---------------------------------------------------------------------------
ROM:FFFF4FD8 loc_FFFF4FD8             ;correction = substract checksum value in file
ROM:FFFF4FD8                 LDRB    R0, [SP,#0x40+var_3C]
ROM:FFFF4FDC                 SUB     R0, R2, R0
ROM:FFFF4FE0                 LDRB    R2, [SP,#0x40+var_3C+1]
ROM:FFFF4FE4                 SUB     R0, R0, R2
ROM:FFFF4FE8                 LDRB    R2, [SP,#0x40+var_3C+2]
ROM:FFFF4FEC                 SUB     R0, R0, R2
ROM:FFFF4FF0                 LDRB    R2, [SP,#0x40+var_3C+3]
ROM:FFFF4FF4                 SUB     R0, R0, R2
ROM:FFFF4FF8                 MVN     R5, R0
ROM:FFFF4FFC                 MOV     R2, R5
ROM:FFFF5000                 ADR     R0, aChecksumXSumX ; "CheckSum=%x sum=%x\n"
ROM:FFFF5004                 BL      printf
ROM:FFFF5008                 LDR     R0, [R4,#0x20]
ROM:FFFF500C                 CMP     R0, R5  ; compare computed and stored sums
ROM:FFFF5010                 BEQ     loc_FFFF501C

autoexec.bin launch

ROM:FFFF40F0                 MOV     R0, #0xF8000000
ROM:FFFF40F4                 LDR     R0, [R0,#8] ;ramexec/bootflag
ROM:FFFF40F8                 CMN     R0, #1
ROM:FFFF40FC                 BEQ     loc_FFFF411C
ROM:FFFF4100                 BL      Read0x10cdf4
ROM:FFFF4104                 BL      CPSR_stuff
ROM:FFFF4108                 MOV     R1, #0x800000
ROM:FFFF410C                 ADR     R0, aRamexec    ; "RAMEXEC"
ROM:FFFF4110                 BL      sub_FFFF315C

jump and back

ROM:FFFF315C sub_FFFF315C             
ROM:FFFF315C                 STMFD   SP!, {R4-R6,LR}
ROM:FFFF3160                 MOV     R5, R0
ROM:FFFF3164                 MOV     R4, R1
ROM:FFFF3168                 MOV     R1, R5
ROM:FFFF316C                 ADR     R0, aNowJumpToS ; "Now jump to %s!!\n"
ROM:FFFF3170                 BL      printf
ROM:FFFF3174                 MOV     R1, R4
ROM:FFFF3178                 MOV     R0, #0
ROM:FFFF317C                 BL      sub_FFFFE75C
ROM:FFFF3180 ; ---------------------------------------------------------------------------
ROM:FFFF3180                 MOV     R1, R5
ROM:FFFF3184                 LDMFD   SP!, {R4-R6,LR}
ROM:FFFF3188                 ADR     R0, aNowReturnedFro ; "Now returned from %s!!\n"
ROM:FFFF318C                 B       printf
ROM:FFFF318C ; End of function sub_FFFF315C

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