More WIP on PPU

sim/tb_top.sv

@@ -138,7 +138,7 @@ assign we      = gb_inst.cpu_we;
 
 assign vram_sel  = gb_inst.vram_sel;
 assign hiram_sel = gb_inst.hiram_sel;
-assign ppu_sel   = gb_inst.ppu_inst.sva_ppu_sel;
+assign ppu_sel   = gb_inst.ppu_inst.ppu_ioregs_inst.sva_sel;
 
 always_ff @(posedge gb_clk or negedge nreset) begin
   if (!nreset)

sim/vgasim.sv

@@ -17,15 +17,18 @@ import "DPI-C" function int vgasim_init(input int screen_h, input int screen_w,
 import "DPI-C" function int vgasim_reset();
 import "DPI-C" function int vgasim_tick(input int r, input int g, input int b, input int hsync, input int vsync);
 
+logic vgasim_initialised = 0;
+
 initial begin
   automatic int ret = vgasim_init(SCREEN_W, SCREEN_H, DEPTH);
-  assert (ret == 0) else begin
+  if (ret != 0) begin
     $display($sformatf("[%0t] vgasim init failed: %d", $time, ret));
-    $fatal();
+  end else begin
+    vgasim_initialised = '1;
   end
 end
 
-always @(negedge nreset) begin
+always @(negedge nreset iff vgasim_initialised) begin
   automatic int ret = vgasim_reset();
   assert (ret == 0) else begin
     $display($sformatf("[%0t] vgasim reset failed: %d", $time, ret));
@@ -33,7 +36,7 @@ always @(negedge nreset) begin
   end
 end
 
-always @(posedge clk iff nreset) begin
+always @(posedge clk iff nreset && vgasim_initialised) begin
   automatic int ret = vgasim_tick(r_i, g_i, b_i, hsync_i, vsync_i);
   assert (ret == 0) else begin
     $display($sformatf("[%0t] vgasim tick failed: %d", $time, ret));