Implemented vsync

Change-Id: I35d7dc7a0184e147faa64fadf038752e7df467b9

src/rgb_to_fb.S

@@ -8,7 +8,7 @@
 //  r0 = pointer to frame buffer
 //  r1
 //  r2
-//  r3
+//  r3 = field offset
 //  r4 = GPLEV0
 //  r5 = line counter
 //  r6 = pixel counter
@@ -18,14 +18,49 @@
 
 rgb_to_fb:
 
-        push    {r4-r12, lr}
+        push   {r4-r12, lr}
 
+        mov    r3, #0
+        ldr    r4, =GPLEV0
+
+frame:
+        // Update field offset to alternate field
+        eor    r3, r3, #320
+        
+        // Set framebuffer address
+        add    r1, r0, r3
+
+        // Wait for start of vsync
+wait_for_vsync_a:
+        ldr    r8, [r4]
+        tst    r8, #VSYNC_MASK
+        beq    wait_for_vsync_a
+
+        // Wait for end of vsync
+wait_for_vsync_b:
+        ldr    r8, [r4]
+        tst    r8, #VSYNC_MASK
+        bne    wait_for_vsync_b
+
+        // Skip inactive lines
+        mov    r5, #28
 loop0:
-        mov     r1, r0
 
-        ldr     r4, =GPLEV0
-        mov     r5, #256
+wait_for_hsync_a:
+        ldr    r8, [r4]
+        tst    r8, #HSYNC_MASK
+        beq    wait_for_hsync_a
 
+wait_for_hsync_b:
+        ldr    r8, [r4]
+        tst    r8, #HSYNC_MASK
+        bne    wait_for_hsync_b
+
+        subs   r5, r5, #1
+        bne    loop0
+
+        // Process active lines
+        mov    r5, #256
 loop1:
 
         // Wait for active high hsync
@@ -87,43 +122,21 @@ wait_psync_10:
         and    r9, r8, #(7 << (PIXEL_BASE + 9))
         orr    r10, r10, r9, lsl #13
 
-
         str    r10, [r1], #4
 
+        subs   r6, r6, #1
+        bne    loop2
 
-        subs    r6, r6, #1
-        bne     loop2
-
-// Skip a whole line
+        // Skip a whole line to maintain aspect ratio
         add    r1, r1, #320
 
-        subs    r5, r5, #1
-        bne     loop1
+        subs   r5, r5, #1
+        bne    loop1
 
-
-// Temporary hack - skip inactive lines
-        ldr     r5, =(312-256)
-                
-loop3:  
-        
-wait_for_hsync_a:
-        ldr    r8, [r4]
-        tst    r8, #HSYNC_MASK
-        beq    wait_for_hsync_a
-
-wait_for_hsync_b:
-        ldr    r8, [r4]
-        tst    r8, #HSYNC_MASK
-        bne    wait_for_hsync_b
-
-        subs    r5, r5, #1
-        bne     loop3
-
-
-        b       loop0
+        b      frame
 
 // Return
 
-        pop     {r4-r12, lr}
-        mov     pc, lr
+        pop    {r4-r12, lr}
+        mov    pc, lr
 

vhdl/RGBtoHDMI.vhdl

@@ -43,6 +43,7 @@ architecture Behavorial of RGBtoHDMI is
     signal shift : std_logic_vector(11 downto 0);
 
     signal nCSYNC1 : std_logic;
+    signal nCSYNC2 : std_logic;
 
     -- The counter runs at 4x pixel clock
     --
@@ -80,15 +81,40 @@ begin
         if rising_edge(clk) then
             -- synchronize nCSYNC to the sampling clock
             nCSYNC1 <= nCSYNC;
+            nCSYNC2 <= nCSYNC1;
 
-            if nCSYNC1 = '0' then
-                -- within horizontal line sync pulse
+            if nCSYNC1 = '0' and nCSYNC2 = '1' then
+                -- start of horizontal line sync pulse
                 hsync <= '1';
                 psync <= '0';
+                -- counter is used to measure how long the pulse is
+                counter <= to_unsigned(0, counter'length);
+                
+            elsif nCSYNC1 = '1' and nCSYNC2 = '0' then
+                -- end of horizontal line sync pulse
+                hsync <= '0';
+                
+                -- test for vertical sync
+                --   a normal line sync pulse is 4us
+                --   a saturated counter (512 == 8us) value can only happen during vsync 
+                if counter = 512 then
+                    vsync <= '1';
+                else
+                    vsync <= '0';
+                end if;
+                    
+                -- counter is used to find sampling point for first pixel
                 counter <= to_unsigned(1311, counter'length);
+
+            elsif nCSYNC1 = '0' then
+                -- within the line sync pulse
+                -- saturate counter at 8us.
+                if counter < 512 then
+                    counter <= counter + 1;
+                end if;
+                
             else
                 -- within the line
-                hsync <= '0';
                 if counter = 31 then
                     counter <= to_unsigned(0, counter'length);
                 else
@@ -110,6 +136,8 @@ begin
         end if;
     end process;
 
+    field <= '1';
+    
     LED1 <= not SW;
 
     LED2 <= led_counter(led_counter'left);