// This code is derived from the video sync generator at
// https://github.com/B-Lang-org/bsc-contrib/blob/main/Libraries/FPGA/Misc/Video.bsv,
// simplified down to serve as an experiment/comparison of synthesis
// efficiency with the sibling directory that has a more imperative
// construction (and also worse, it tursn out).

package Top;

import Counter::*;
import StmtFSM::*;

typedef struct {
   Integer     active;
   Integer     fporch;
   Integer     sync;
   Integer     bporch;
} SyncDescriptor;

SyncDescriptor horizontal = SyncDescriptor{
   active: 640,
   fporch: 16,
   sync: 96,
   bporch: 48
};

SyncDescriptor vertical = SyncDescriptor{
   active: 480,
   fporch: 10,
   sync: 2,
   bporch: 33
};

interface SyncGenerator;
   method    Action      tick();
   method    Bool        preedge();
   method    Bool        out_n();
   method    Bool        out();
   method    Bool        active();
endinterface

module mkSyncGenerator#(SyncDescriptor info)(SyncGenerator);
   let maxActive = fromInteger(info.active - 1);
   let maxFPorch = fromInteger(info.fporch - 1);
   let maxSync   = fromInteger(info.sync   - 1);
   let maxBPorch = fromInteger(info.bporch - 1);

   /////////////////////
   /// Design Elements
   /////////////////////
   Counter#(16)                    rCounter            <- mkCounter(0);

   PulseWire                       pwTick              <- mkPulseWire;
   PulseWire                       pwPreSyncEdge       <- mkPulseWire;
   Reg#(Bool)                      rSyncOut            <- mkReg(True);
   Reg#(Bool)                      rActive             <- mkReg(False);

   /////////////////////
   /// Rules
   /////////////////////
   Stmt machine =
   seq
      while(True) seq
	 // Front Porch
	 while(rCounter.value < maxFPorch) action
	    rCounter.up;
	 endaction

	 action
	    rCounter.clear;
	    pwPreSyncEdge.send;
	    rSyncOut   <= False;
	    rActive    <= False;
	 endaction

	 // Sync Pulse
	 while(rCounter.value < maxSync) action
	    rCounter.up;
	 endaction

	 action
	    rCounter.clear;
	    rSyncOut  <= True;
	    rActive   <= False;
	 endaction

	 // Back Porch
	 while(rCounter.value < maxBPorch) action
	    rCounter.up;
	 endaction

	 action
	    rCounter.clear;
	    rSyncOut  <= True;
	    rActive   <= True;
	 endaction

	 // Active
	 while(rCounter.value < maxActive) action
	    rCounter.up;
	 endaction

	 action
	    rCounter.clear;
	    rSyncOut  <= True;
	    rActive   <= False;
	 endaction
      endseq
   endseq;

   FSM fsmSyncGen <- mkFSMWithPred(machine, pwTick);

   rule start_sync_generator(fsmSyncGen.done);
      fsmSyncGen.start;
   endrule

   method Action tick     = pwTick.send;
   method Bool   preedge  = pwPreSyncEdge;
   method Bool   out_n    = rSyncOut;
   method Bool   out      = !rSyncOut;
   method Bool   active   = rActive;
endmodule: mkSyncGenerator

interface ITop;
   (* always_ready *)
   method Bool paint();
   (* always_ready *)
   method Bool hsync();
   (* always_ready *)
   method Bool vsync();
endinterface

(* synthesize *)
module mkTop (ITop);
   let horiz <- mkSyncGenerator(horizontal);
   let vert  <- mkSyncGenerator(vertical);

   (* no_implicit_conditions, fire_when_enabled *)
   rule advance_horizontal;
      horiz.tick;
   endrule

   (* no_implicit_conditions, fire_when_enabled *)
   rule advance_vertical (horiz.preedge);
      vert.tick;
   endrule

   method Bool paint = horiz.active && vert.active;
   method Bool hsync = horiz.out;
   method Bool vsync = vert.out;
endmodule

endpackage