The Zilog Z80 microprocessor is a popular choice for embedded systems and retro computing enthusiasts. While it was originally designed to work with assembly language, it is also possible to write C++ code for this architecture using compiler-specific extensions. This blog post will explore some of the Z80 C++ compiler-specific extensions and how they can be used to optimize code for this specific platform.

1. Register Variables

int main() {
  register int a asm("a") = 10;
  register int b asm("b") = 20;
  register int result asm("c");

  asm("add %1, %2" : "=c"(result) : "a"(a), "b"(b));

  return result;
}

Using the register keyword and the asm directive, we can allocate variables to specific registers of the Z80 processor. This can lead to more efficient code generation, as data can be directly manipulated using the CPU registers. In the example above, we define three register variables a, b, and result tied to the Z80 registers a, b, and c, respectively. We then use inline assembly to perform addition between a and b, storing the result in result.

2. Inline Assembly

int main() {   
  int result;
  int data = 42;

  asm("ld a, %1" : "=a"(result) : "r"(data));

  return result;
}

The Z80 C++ compiler-specific extensions allow us to use inline assembly to directly write Z80 assembly instructions within our C++ code. In the example above, we load the value of data into the a register using the Z80 assembly instruction ld a, %1. The result is then stored in the result variable using the output constraint =a.

Conclusion

Zilog Z80 C++ compiler-specific extensions provide developers with the ability to write optimized code for this specific microprocessor architecture. By utilizing register variables and inline assembly, it is possible to take full advantage of the Z80’s capabilities and achieve better performance in Z80-based systems.

#Z80 #C++ #embedded #retrocomputing