Issue657 (#755)

Fix for #657
- cps1: fix color DMA (wr_page advances too soon) ()
- cps1: try BFF as blank color (#657)
- cps2: blank to black after the color DMA fix (#657)
- cps2: don't blank over sprites (#657)
- cps2: simplify obj/scr mux (by paulb-nl) (#657)

cores/cps1/hdl/jtcps1_colmix.v

@@ -130,10 +130,11 @@ always @(*) begin
     endcase
 end
 
-`ifdef CPS2
-localparam [13:0] BLANK_PXL = { 2'b11, 12'hBFF }; // according to DL-0921 RE but it doesn't look
-// good on CPS1/CPS1.5 games. CPS2 is fine with that
+`ifndef CPS2
+localparam [13:0] BLANK_PXL = { 2'b11, 12'hBFF }; // according to DL-0921 RE
 `else
+// CPS2 seems to blank to black, as the programmed color in CPS1 is expanding to the back porch area,
+// confusing the black level calibration on displays.
 localparam [13:0] BLANK_PXL = ~14'd0;
 `endif
 

cores/cps1/hdl/jtcps1_dma.v

@@ -119,6 +119,7 @@ localparam MW = 3; // miss hit counter
 reg  [15:0] vrenderf, vscr1, vscr2, vscr3, row_scr_next;
 reg  [11:0] scan;
 wire [11:0] wr_pal_addr;
+wire [15:0] pal_ram_q;
 reg  [10:0] vn, hn, hstep;
 reg  [ 9:0] obj_cnt, obj_wr_cnt;
 reg  [ 8:0] pal_cnt, pal_wr_cnt, vram_scr_base;
@@ -236,10 +237,13 @@ jtframe_dual_ram #(.DW(16), .AW(12)) u_pal_ram(
     .addr1  ( colmix_addr   ),
     .we1    ( 1'b0          )
     `ifndef FORCE_GRAY
-    ,.q1    ( pal_data      )
+    ,.q1    ( pal_ram_q     )
     `endif
 );
 
+// handle artificial CPS2 blank color (FFF)
+assign pal_data = colmix_addr == 12'hFFF ? 16'h0 : pal_ram_q;
+
 `ifdef FORCE_GRAY
 assign pal_data = {4'hf, {3{colmix_addr[3:0]}} };
 `endif
@@ -483,11 +487,13 @@ always @(posedge clk) begin
                         end
                         if( |cur_task[PAL5:PAL0] ) begin
                             pal_cnt <= pal_cnt + 9'd1;
-                            if( &pal_cnt ) begin
+                            if( &pal_wr_cnt ) begin
                                 tasks[PAL5:PAL0] <= tasks[PAL5:PAL0] & ~cur_task[PAL5:PAL0];
                                 adv <= 1;
                                 // Update palette page
                                 pal_wr_page <= pal_wr_page+3'd1;
+                            end
+                            if( &pal_cnt ) begin
                                 pal_rd_page<=pal_rd_page+3'd1;
                             end
                         end

cores/cps2/hdl/jtcps2_colmix.v

@@ -39,7 +39,7 @@ module jtcps2_colmix(
 localparam [2:0] OBJ=3'b0, SCR1=3'b1, SCR2=3'd2, SCR3=3'd3, STA=3'd4;
 localparam [3:1] OBJ_PRIO = 3'b010;
 
-reg         obj1st, mux_sel;
+reg         obj1st, obj_sel;
 reg  [ 3:0] scr_prio;
 reg  [15:0] lyr_prio;
 
@@ -61,7 +61,7 @@ always @(*) begin
         default: scr_prio = 4'd7;
     endcase
     obj1st = obj_prio > scr_prio[2:0];
-    mux_sel = obj1st ? blank(obj_pxl) : ~blank(scr_pxl);
+    obj_sel = ~blank(obj_pxl) & (obj1st | blank(scr_pxl));
 end
 
 always @(posedge clk) begin
@@ -72,8 +72,7 @@ always @(posedge clk) begin
 end
 
 always @(posedge clk) if(pxl_cen) begin
-    pxl <= !obj_en ? scr_pxl :
-        ( mux_sel ? scr_pxl : {3'd0, obj_pxl[8:0]} );
+    pxl <= (obj_en & obj_sel) ? {3'd0, obj_pxl[8:0]} : scr_pxl;
 end
 
 `ifdef PRIO_SIM