fix: widen native video centering range

Author: wizzomafizzo

menu.sv

@@ -208,14 +208,13 @@ assign LED_POWER[0]= FB ? led[2] : act_cnt2[26] ? act_cnt2[25:18] > act_cnt2[7:0
 
 
 `include "build_id.v" 
-// Image centering: 4-bit signed in OSD ordering 0,+1..+7,-8..-1 so that the
-// power-on default (status bits = 0) maps to "no shift". Bit pattern matches
-// 4-bit two's complement when reinterpreted as signed.
+// Image centering options use signed two's-complement ordering with 0 first,
+// so the power-on default (status bits = 0) selects the calibrated base timing.
 localparam CONF_STR = {
 	"MENU;UART31250,MIDI;",
 	"-;",
-	"O[13:10],H Offset,0,+1,+2,+3,+4,+5,+6,+7,-8,-7,-6,-5,-4,-3,-2,-1;",
-	"O[17:14],V Offset,0,+1,+2,+3,+4,+5,+6,+7,-8,-7,-6,-5,-4,-3,-2,-1;",
+	"O[15:10],H Offset,0,+1,+2,+3,+4,+5,+6,+7,+8,+9,+10,+11,+12,+13,+14,+15,+16,+17,+18,+19,+20,+21,+22,+23,+24,+25,+26,+27,+28,+29,+30,+31,-32,-31,-30,-29,-28,-27,-26,-25,-24,-23,-22,-21,-20,-19,-18,-17,-16,-15,-14,-13,-12,-11,-10,-9,-8,-7,-6,-5,-4,-3,-2,-1;",
+	"O[19:16],V Offset,0,+1,+2,+3,+4,+5,+6,+7,-8,-7,-6,-5,-4,-3,-2,-1;",
 	"-;",
 	"V,v",`BUILD_DATE
 };
@@ -522,12 +521,10 @@ native_video_top native_video
 	.enable         (mode_zaparoo),
 	.active         (native_active),
 
-	// status[13:10] / status[17:14] are 4-bit fields whose bit pattern
-	// matches signed two's complement when the OSD enum is ordered
-	// 0,+1..+7,-8..-1 (see CONF_STR). $signed() makes the reinterpretation
-	// explicit at the port boundary.
-	.h_offset       ($signed(status[13:10])),
-	.v_offset       ($signed(status[17:14]))
+	// Status bit patterns match signed two's complement because CONF_STR orders
+	// each OSD enum as 0,+1..max,min..-1. $signed() makes that explicit here.
+	.h_offset       ($signed(status[15:10])),
+	.v_offset       ($signed(status[19:16]))
 );
 
 // Cosine + LFSR fallback noise pattern, painted into the 320x240 active area

rtl/native_video_timing.sv

@@ -1,7 +1,6 @@
 // Zaparoo native video timing: 320x240 at 15.734 kHz from 27 MHz / 4.
-// h_offset/v_offset (signed -8..+7) shift the image by repartitioning
-// front porch and back porch. H_TOTAL/V_TOTAL are invariant, so line
-// rate and frame rate are unchanged regardless of offset values.
+// h_offset/v_offset shift the image by repartitioning front porch and back
+// porch. H_TOTAL/V_TOTAL are invariant, so line/frame rates stay unchanged.
 
 module native_video_timing
 (
@@ -10,8 +9,8 @@ module native_video_timing
 	input  wire       reset,
 
 	// Image centering: positive = shift right/down (FP shrinks, BP grows).
-	input  wire signed [3:0] h_offset,  // -8..+7 pixels (budget H_FP=14 / H_BP=63)
-	input  wire signed [3:0] v_offset,  // -8..+7 lines  (budget V_FP=8 / V_BP=11)
+	input  wire signed [5:0] h_offset,  // -32..+31 pixels (budget H_FP=38 / H_BP=39)
+	input  wire signed [3:0] v_offset,  // -8..+7 lines   (budget V_FP=8 / V_BP=11)
 
 	output reg        hsync,
 	output reg        vsync,
@@ -25,9 +24,11 @@ module native_video_timing
 );
 
 localparam [9:0] H_ACTIVE = 10'd320;
-localparam [9:0] H_FP     = 10'd14;
+// 38/32/39 keeps total blanking fixed while moving the default image 24 px
+// left from the earlier CRT-specific 14/32/63 porch split.
+localparam [9:0] H_FP     = 10'd38;
 localparam [5:0] H_SYNC   = 6'd32;
-localparam [9:0] H_BP     = 10'd63;
+localparam [9:0] H_BP     = 10'd39;
 localparam [9:0] H_TOTAL  = 10'd429;
 
 // V blanking rebalanced from 6/3/13 to 8/3/11 to give symmetric ±8 budget
@@ -40,7 +41,7 @@ localparam [8:0] V_TOTAL  = 9'd262;
 
 // Sync starts shift with the offset; two's-complement subtraction in
 // unsigned arithmetic yields the correct result at both ends of the range.
-wire [9:0] H_SYNC_START = H_ACTIVE + (H_FP - {{6{h_offset[3]}}, h_offset});
+wire [9:0] H_SYNC_START = H_ACTIVE + (H_FP - {{4{h_offset[5]}}, h_offset});
 wire [9:0] H_SYNC_END   = H_SYNC_START + H_SYNC;
 wire [8:0] V_SYNC_START = V_ACTIVE + (V_FP - {{5{v_offset[3]}}, v_offset});
 wire [8:0] V_SYNC_END   = V_SYNC_START + V_SYNC;

rtl/native_video_top.sv

@@ -31,8 +31,8 @@ module native_video_top
 	input  wire        enable,
 	output wire        active,
 
-	// OSD image centering: signed -8..+7 pixels/lines, 0 = no shift.
-	input  wire signed [3:0] h_offset,
+	// OSD image centering: 0 = default porch split.
+	input  wire signed [5:0] h_offset,
 	input  wire signed [3:0] v_offset
 );