I am new to VHDL, but I have managed to create a processor in VHDL with some help (it has ALU, multiplier, and a bus architecture to access SRAM memory). The processor decodes 32-bit instructions (which contains the type of operations and the memory addresses).
How do I write the following C code in the processor?
int i = 0;
int c = 0;
int a[10] = "0,1,2,3,4,5,6,7,8,9";
int b[10] = "1,0,-1,0,1,0,2,1,-1,1";
for (i = 0; i < 9; i++) c += (a[i]*b[i]);
I'm guessing I would write a list of instructions for this C code in the testbench:
1st instruction: multiply a[0] with b[0]
2nd instruction: add the result to c
and repeat for 9 times.
Is this the right way? Is there a better way to implement the for-loop? Is there a way to write C-code directly in my tb_top.vhd?
Of course, you can manually translate the C code to assembler code, and then assemble this to binary code. But, a better option is to use a C compiler and / or assembler for your processor. If there is no one available and you plan to use your processor for longer / many programs, you can build a new compiler on top of gcc and a new assembler on top of binutils, for example.
Then place the binary output into the instruction ROM. If you simulate the processor itself without memory and I/O devices, then emulate the instruction ROM in your testbench. An array of std_logic_vector should fit your needs:
type rom_t is array(natural range <>) of std_logic_vector(7 downto 0) ;
constant rom : rom_t(0 to 63) := (
0 => x"00", -- insert binary code of instruction at address 0 here
1 => x"00", -- instruction at address 1
-- and so on
others => x"00" -- fill remaining ROM with zero
);
The example defines a ROM with 64 addresses, each storing a byte. You will have to update the ranges and the memory content to fit your needs.