Modules, Hierarchy, Composability

Feed forward nested functions

// sub.c
output_t sub(input_t input)
{
  // Do work on input to get output 
  return work(input);
}

// top.c
#include "sub.c"
output_t top(input_t input)
{
  return sub(input);
}

Point to point wires between modules

// top.c
// Globally visible ports/wires with built in READ and WRITE
input_t top_to_sub; // Output from top, input to sub
output_t sub_to_top; // Input into top, output from sub
output_t top(input_t input)
{
  WRITE(top_to_sub, input);
  return READ(sub_to_top);
}

// sub.c
#include "top.c"
void sub()
{
  // Do work on input to get output
  input_t input = READ(top_to_sub);
  output_t output = work(input);
  WRITE(sub_to_top, output);
}

Using both - debug/status LEDs example

As opposed to rewiring the LEDs manually through the ports of top,sub, and work using a globally visible point to point wire makes reading and writing arbitrary signals in the design possible.

// leds.c
// Globally visible port/wire name
uint4_t leds; 
uint4_t leds_module()
{
  // Drive the output port with the global wire
  return READ(leds);
}

#include "leds.c"
output_t work(input_t input)
{
  // Doing lots of complicated stuff
  // ...
  // Lets drive status leds
  uint4_t leds = 0xF;
  WRITE(leds);
  // ...
} 
output_t sub(input_t input)
{
  return work(input);
} 
output_t top(input_t input)
{
  return sub(input);
}

C Syntax

The above code snippets are pseudo code as the real C syntax is a bit uglier for global wires (a type of non volatile clock crossing wires).