Infineon C167CR Register & Memory Segmentation Architecture
Reverse engineering BMW firmware requires mastery of two dominant automotive microcontroller architectures: the 16-bit Infineon C167CR (Era 2) and the 32-bit unified TriCore TC1796 / AURIX TC298 (Era 3 & 4).
17.1 Infineon C167CR Register & Memory Segmentation Architecture#
The C167CR-LM (clocked at 24 ext{ MHz} in MS43) utilizes a 16-bit core with 24-bit segmented addressing, providing an addressable physical space of 16 ext{ Megabytes}:
- Segmented Memory Model: Addresses are divided into 64 ext{ KB} segments (
Segment 0=0x000000 - 0x00FFFF,Segment 7=0x070000 - 0x07FFFF).DPP0(SFR0xFE00): Points to Flash Program Constants.DPP1(SFR0xFE02): Points to Extended Calibration Maps.DPP2(SFR0xFE04): Points to Internal Dual-Port SRAM (0xFA00 - 0xFDFF).DPP3(SFR0xFE06): Points to Special Function Registers (SFRs) and System Stack.
- Data Page Pointers (DPP0 - DPP3): Because 16-bit pointers can only span 16 ext{ KB} data pages, four 10-bit Data Page Pointers select which 16 ext{ KB} physical memory block is active:
┌──────────────────────────────────────────────────────────────────────────────────────────────────┐
│ INFINEON C167CR MEMORY SEGMENTATION & DPP ADDRESS TRANSLATION │
├──────────────────────────────────────────────────────────────────────────────────────────────────┤
│ │
│ 16-Bit Near Address: [ Page Selector: 2 Bits ] [ 14-Bit Offset: 0x0000 to 0x3FFF ] │
│ │ │
│ ▼ │
│ Selects DPP0, DPP1, DPP2, or DPP3 (10 Bits) │
│ │ │
│ ▼ │
│ 24-Bit Physical Address: [ DPPx Base Address: 10 Bits ] [ 14-Bit Offset ] ──► 16 MB Range │
└──────────────────────────────────────────────────────────────────────────────────────────────────┘ C167CR Assembly Disassembly Example (MS43 Ignition Angle Fetch):#
; ==============================================================================
; Routine: Sub_Fetch_Ignition_Advance_98RON
; Input: R12 = Engine Speed (RPM), R13 = Relative Load (mg/stroke)
; Output: R4 = Base Ignition Advance (Degrees)
; ==============================================================================
sub_5B210:
MOV R1, #0x7048 ; Load Base Address of ip_iga_ron_98_pl (Page 0x1C)
MOV DPP1, #0x001C ; Set DPP1 to point to 64 KB Calibration Block (0x70000)
EXTP DPP1, #1 ; Extend next instruction to utilize DPP1 page
MOV R2, [R1] ; Read Number of Columns (16)
CALLA cc_UC, Map_Interp_2D ; Branch to 2D Surface Bilinear Interpolator
MOV R4, R14 ; Return Interpolated Raw Advance Word in R4
RETS ; Return from Subroutine 17.2 TriCore TC1796 32-Bit RISC/DSP Architecture (MSD80 / EDC17)#
The Infineon TriCore architecture merges a 32-bit RISC processing core, digital signal processor (DSP), and autonomous micro-controller onto a single chip:
- Context Save Areas (CSA): Rather than pushing registers onto an external memory stack during interrupts, the TC1796 contains a dedicated high-speed hardware link list of 64-byte Context Save Areas in internal SRAM:
- Code Cave Hooking on MSD80: Calibrators add custom logic (e.g. 2-step rev limiters) by overwriting unused padding bytes at
0x001FE000and inserting a 32-bit direct jump: ``assembly J 0x801FE000 ; Jump absolute to custom code cave in cached flash segment``