Thread: Garmin eTREX 20 working as an eTREX 30

Just wondering, what happens if we make MOVS R1,#1 or MOVS R1,#5, which also corespond to eTrex 30 (this fact can be seen at sub_801FAFAA).

Code:

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BTW, MOVS R0, R0 is not a good way to insert a NOP instruction, as it may affect flags in CPSR register.

if we put 1 or 5, the gps work but the screen go entire white.
If indeed the instruction mov r0, r0 not a good idea.
I searched other direction where most major patch this.

Firmware version 2.80

ROM:80203732 sub_80203732 ; CODE XREF: ROM:802037D4p
ROM:80203732 LDR R0, =0x12009000 ; Load from Memory
ROM:80203734 PUSH {R4,LR} ; Push registers
ROM:80203736 LDR R3, =0x40014D4 ; Load from Memory
ROM:80203738 LDR R2, [R0,#0x20] ; Load from Memory
ROM:8020373A MOVS R1, 0x1E0000
ROM:8020373E ORRS R2, R1 ; Rd = Op1 | Op2
ROM:80203740 STR R2, [R0,#0x20] ; Store to Memory
ROM:80203742 LDR R2, [R0,#0x24] ; Load from Memory
ROM:80203744 BICS R2, R1 ; Rd = Op1 & ~Op2
ROM:80203746 STR R2, [R0,#0x24] ; Store to Memory
ROM:80203748 LDR R0, [R0] ; Load from Memory
ROM:8020374A LSLS R0, R0, #0xB ; Logical Shift Left
ROM:8020374C LSRS R0, R0, #0x1C ; Logical Shift Right ; Patch to: MOVS R0, #3
ROM:8020374E STRB R0, [R3] ; Store to Memory
ROM:80203750 LDRB R0, [R3] ; Load from Memory
ROM:80203752 STRB R0, [R3,#1] ; Store to Memory
ROM:80203754 BL sub_80200AD0 ; Branch with Link
ROM:80203758 POP {R4,PC} ; Pop registers
ROM:80203758 ; End of function sub_80203732

Originally Posted by kunix

Just wondering, what happens if we make MOVS R1,#1 or MOVS R1,#5, which also corespond to eTrex 30 (this fact can be seen at sub_801FAFAA).

Code:

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BTW, MOVS R0, R0 is not a good way to insert a NOP instruction, as it may affect flags in CPSR register.

I can confirm.
There are at least two models of PCBs, for etrex20/30.

Model1: In Memory 0x12009000 (i think model of PCB) -> 0x00043f3d
r0 = 2 for etrex20
r0 = 3 for etrex30

Model2: in Memory 0x12009000 (i think model of PCB) ---> Not looked yet.
r0 = 4 for etrex20
r0 = 5 for etrex30

The function that maps the gps model according to the motherboard.

Code:

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