Systemc

Language standard pins:

• Reference Model: C11 (-std=c11), pure C, standalone — compilable without SystemC
• BFM/SystemC: C++17 (-std=c++17); C++20 features (concepts, ranges, coroutines, modules) forbidden

1. Naming Conventions

1.1 Filenames

1.2 Class/Module Naming

1.3 Port Naming (RTL Matching)

SystemC ports use the same names as their RTL counterparts:

sc_in<sc_uint<8>>  i_data{"i_data"};
sc_out<bool>        o_valid{"o_valid"};
sc_in<bool>         sys_clk{"sys_clk"};       // clock: no i_/o_ prefix
sc_in<bool>         sys_rst_n{"sys_rst_n"};   // reset: no i_/o_ prefix

2. Bit-Exactness Rules (Reference Model)

Core principles:

• Bit-accurate: must guarantee identical bit-level results as the RTL
• Cycle-agnostic: implements only the algorithm, no timing concepts
• Deterministic: same input → same output (no random, no float)
• Standalone: compilable as pure C without SystemC

Fixed-point rules:

• Fixed-width integers only (int16_t, uint32_t); no int (platform-dependent width), no float/double
• Explicitly specify overflow behavior: saturate vs wrap

// CORRECT: bit-exact fixed-point multiply
int32_t fixed_mul(int16_t a, int16_t b) {
  return static_cast<int32_t>(a) * static_cast<int32_t>(b);
}
// WRONG: 'int result = a * b;' — implicit promotion may differ from RTL

3. BFM Rules

• Cycle-accurate: produce results in the same number of cycles as RTL
• AT non-blocking by default; LT only when explicitly requested (see Execution_Policy)
• Separate pin-adapter: keep TLM abstraction separate from the pin-level interface (sc_signal RTL wrapper + optional DPI-C bridge to SV TB)
• Timing values derive from timing_constraints.json — no magic wait(2.0, SC_NS) numbers
• Every model needs an sc_main testbench; always call set_response_status() before returning

4. Build Rules

# Reference Model (standalone C, no SystemC)
gcc -std=c11 -O2 -Wall -Wextra -Werror -shared -fPIC -o ref_cabac.so ref_cabac.c

# BFM (SystemC required)
g++ -std=c++17 -O2 -Wall -Wextra \
  -I${SYSTEMC_HOME}/include -L${SYSTEMC_HOME}/lib-linux64 -lsystemc \
  -o tb_cabac tb_cabac_top.cpp bfm_cabac.cpp

# cocotb integration (shared library, C ref model)
gcc -std=c11 -shared -fPIC -o ref_cabac.so ref_cabac.c

cocotb integration:

import ctypes
lib = ctypes.CDLL("./ref_cabac.so")
lib.encode_bin.restype = ctypes.c_uint32
lib.encode_bin.argtypes = [ctypes.c_uint16, ctypes.c_bool]
expected = lib.encode_bin(ctx_addr, bin_val)

5. Coding Style

Mandatory:

• C++17 (not C++20), fixed-width integers (<cstdint>), RAII, const, header guard
• AT models: MemoryManager (payload pooling via tlm_mm_interface, p->reset() in free()) + PEQ

Prohibited:

• float/double in bit-exact models; platform-dependent int
• malloc/free (use RAII); using namespace std; in headers
• LT b_transport in performance BFMs (use AT); missing AT phase transitions (implement all 4 phases with PEQ)
• Blocking DPI calls that deadlock (queue to SC_THREAD for async handling)