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peter.halford@alarmip.com · Guest

Dear Group,

I am designing an LCD controller, straight VGA using a 6.5" TFT (60Hz
and a 25MHz dot clock) with a 32MBit SDRAM frame buffer (using two
Xilinx block RAMs as alternate line buffers).

Xilinx ISE 7.1 development environment.

I also designed the hardware: a BlackFin BF532 CPU/ROM/SDRAM with a
Xilinx Spartan-3 (XC3S400-4PQ208C) handling the general I/F
requirements and VGA display. It is a 4-layer PCB with a 25MHz master
clock.

Until now, all my coding has been with VHDL and everything has
simulated correctly.

Come on now... Just how difficult can it be? Or so I thought.

Well, everything works just fine for about 200ms (correct syncs etc...)
and then things go dead for 800ms -- no syncs, nothing. And then things
spring back to life for another 200ms ad nauseam...

The internal clocks are running fine (I have some spare signals on the
FPGA to which I can bind some debug signals).

Since I am pretty much a newbie to VHDL, I figured I would design a
replacement VGA module using gate-level logic (counters, comparators
and so on) but it generates exactly the same results.

The power supplies appear to be clean. The BlackFin continues to work
with a command-line UBOOT serial link.

This project has taken 6-weeks longer than it needed to. I look an
idiot (which I probably am) and only the thought of how much pleasure
it would give my mother-in-law stops me from 'doing myself in'...

Any kind or informative suggestions would be very much appreciated.

Regards & seasonal greetings to all.

Peter

Ed McGettigan · Guest

There isn't enough info in your post to provide any detailed debugging
opinion, but it looks like you must have misunderstood something in
either the way that the Blackfin or TFT interfaces works as both
your VHDL code and your gate-level code fail in the same way.

You have a repeatable and consistent problem which is much better than
a random failure so you should be able to track down the culprit.

If you included a JTAG port on your PCB that is connected to the 3S400
then I would suggest that you try inserting a ChipScope ILA debug core
into your design. This will give you the ability to probe and trigger
on the internal buses to see where the failure is. If you don't already
have a license for this you can get a 60-day full feature eval at
http://www.xilinx.com/chipscope that should be plenty of time to find
and correct your problem.

Ed

peter.halford@alarmip.com wrote:

Dave · Guest

peter.halford@alarmip.com · Guest

Bottle is already open...

Living in Greece, can I suggest how nice: CAIR sparkling-wine is. It is
methode-Champagnoise (meaning it is made in the same way as the
sparkling wine from the Champagne region of France), but at a fraction
of the cost. Actually, it is made in Rhodes (a rather large Island here
in Greece).

However, all I can think is that somehow the BlackFin is resetting the
array. Unfortunately, I didn't write any of the code nor UBOOT, so I
guess tomorrow (they're very small legs and too much CAIR) I will look
at all of the FPGA control signals...

Please keep the suggestions coming (apart that is from YOU,
mother-in-law).

Peter

Jim Granville · Guest

peter.halford@alarmip.com wrote:

bh · Guest

<peter.halford@alarmip.com> wrote in message
news:1135270697.315589.100480@g44g2000cwa.googlegroups.com...

Sylvain Munaut · Guest

peter.halford@alarmip.com wrote:

dp · Guest

peter.halford@alarmip.com · Guest

Dear All,

Many thanks for all your suggestions...

I have tried dividing my incoming 25MHz clock by 2 and voilla!
everything works, albeit 50% slower...

So now I guess I will have to divide the incoming clock by 2, multiply
it and re-divide it.

Any ideas why this could be happening?

Regards to all,
Peter

Phil Hays · Guest

peter halford wrote:

peter.halford@alarmip.com · Guest

Dear Group,

I know how annoying it is when one posts blocks of HDL, but I would
really appreciate someone telling me why this code does not work -- or
at least, a pointer to my stupidity!!!

This HDL is supposed to generate standard -ve syncs plus an early
'newline' signal to a specialised SDRAM controller which writes a
complete line of octets into alternate block-RAMs in my Spartan-3
device.

It then attempts to display them by generating alternate read enables
(based on the current vertical line).

Tomorrow I am going to rewrite the code using discrete processes (one
for each sync signal etc...).

library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.std_logic_unsigned.all;
use IEEE.numeric_std.all;

entity VidCont is
generic(
DATA_WIDTH : natural := 16; -- video data width
VADDR_WIDTH : natural := 10 -- Video FIFO
(blockRAM) address width
);
port(
-- Interface
clk : in std_logic; -- Master clock @25MHz
rst : in std_logic; -- Reset
-- Video blockRAM side
VIAddr : out std_logic_vector(VADDR_WIDTH-1 downto 0);
-- Video line buffer address
VADIn : in std_logic_vector(DATA_WIDTH-1 downto 0);
-- Data from 'A' block RAM
VEnA : out std_logic; -- Enable 'A' FIFO
VBDIn : in std_logic_vector(DATA_WIDTH-1 downto 0);
-- Data from 'B' block RAM
VEnB : out std_logic; -- Enable 'B' FIFO
NewLine : out std_logic; -- Initiate line read burst
-- TFT interface
VRed : out std_logic_vector(5 downto 0); -- 6-bit
red
VGreen : out std_logic_vector(5 downto 0); -- 6-bit
green
VBlue : out std_logic_Vector(5 downto 0); -- 6-bit
blue
VDE : out std_logic; -- Data-enable
VVSync : out std_logic; -- Vertical synch.
VHSync : out std_logic; -- Horizontal synch.
-- Debug signal...
Debug : out std_logic
);
end VidCont;

architecture arch of VidCont is

constant YES : std_logic := '1';
constant NO : std_logic := '0';
constant HI : std_logic := '1';
constant LO : std_logic := '0';
constant ONE : std_logic := '1';
constant ZERO : std_logic := '0';

-- TFT timing parameters...
constant tHP : natural := 800; -- Horizontal sync. period
constant tWH : natural := 96; -- Horizontal sync. width
constant tVP : natural := 525; -- Vertical sync. period
constant tWV : natural := 2; -- Vertical sync. width
constant tHV : natural := 640; -- Active horizontal period
constant tHBP : natural := tWH+40; -- End of H back porch (start
of active area)
constant tHFP : natural := tHBP+tHV; -- Start of H front porch (end
of active area)
constant tVV : natural := 480; -- Active vertical period
constant tVBP : natural := tWV+33; -- End of V back porch (start
of active area)
constant tVFP : natural := tVBP+tVV; -- Start of V front porch (end
of active area)

-- Horizontal & vertical counters...
signal hCount_x, hCount_r : natural range 0 to tHP+1;
-- Horizontal column count
signal vCount_x, vCount_r : natural range 0 to tVP+1;
-- Address counters...
signal hAddr_x, hAddr_r :
std_logic_vector(VIAddr'range); -- Horizontal address
-- Data enable flags...
signal hDEm3_x, hDEm3_r : std_logic; -- Early (-3)
horizontal data enable
signal hDEm2_r : std_logic; -- Early (-2)
latched horizontal data enable
signal hDEm1_r : std_logic; -- Early (-1)
latched horizontal data enable
signal hDE_r : std_logic; -- Horizontal
data enable
signal vDEm2_x, vDEm2_r : std_logic; -- Early (-2)
vertical data enable
signal vDEm1_r : std_logic; -- Early (-1)
vertical data enable
signal vDE_r : std_logic; -- Vertical
data enable
signal nlBurst_x, nlBurst_r : std_logic; -- Newline
burst strobe
signal IVEnA_x, IVEnA_r : std_logic; -- Block RAM
'A' read enable
signal IVEnB_x, IVEnB_r : std_logic; -- Block RAM
'B' read enable
-- Syncs...
signal IVSync_x, IVSync_r : std_logic; -- Vertical
sync
signal IHSync_x, IHSync_r : std_logic; -- Horizontal
sync
signal AltLine_x, AltLine_r : std_logic; -- Source
flipper
-- RGB data...
signal RGB_x, RGB_r :
std_logic_vector(VADIn'range); -- Demultiplexed and latched RGB data

begin

-- Attach signals to outputs...
VIAddr <= hAddr_r; -- Horizontal address = block RAM address
VDE <= hDE_r; -- Display enable...
VRed(5 downto 1) <= RGB_r(15 downto 11);
VRed(0) <= RGB_r(15);
VGreen(5 downto 0) <= RGB_r(10 downto 5);
VBlue(5 downto 1) <= RGB_r(4 downto 0);
VBlue(0) <= RGB_r(4);
VHSync <= IHSync_r;
VVSync <= IVSync_r;
VEnA <= IVEnA_r;
VEnB <= IVEnB_r;
NewLine <= nlBurst_r;
Debug <= IHSync_r;

-- Determine next state...
RGB_x <= VBDIn when AltLine_r = '0' else VADIn; -- Video input mux
IHSync_x <= LO when hCount_r = (tHP-1) else HI when hCount_r =
(tWH-1) else IHSync_r; -- Hor. sync generation
IVSync_x <= LO when vCount_r = (tVP-1) else HI when vCount_r =
(tWV-1) else IVSync_r; -- Vert. sync generation
hCount_x <= 0 when hCount_r = (tHP-1) else hCount_r + 1; -- Hor.
counter
vCount_x <= 0 when vCount_r = (tVP-1) else vCount_r + 1 when hCount_r
= (tHP-1) else vCount_r; -- Vert. counter
AltLine_x <= LO when vCount_r = (tVP-1) else not AltLine_r when
hCount_r = (tHP-1) else AltLine_r; -- Alternate line generation
hDEm3_x <= HI when (hCount_r = (tHBP-1)) and (vDEm2_r = HI) else LO
when hCount_r = (tHFP-1) else hDEm3_r; -- Early horizontal DE
vDEm2_x <= HI when vCount_r = (tVBP-1) else LO when vCount_r =
(tVFP-1) else vDEm2_r; -- Early vertical DE
nlBurst_x <= HI when (vDEm1_r = '1') and (hCount_r = (tWH-1)) else
LO; -- BlockRAM fill strobe
hAddr_x <= hAddr_r + 1 when hDEm2_r = '1' else (others => '0'); --
Keep advancing blockRAM address during active window, else reset
IVEnA_x <= HI when AltLine_r = '1' else LO;
IVEnB_x <= HI when AltLine_r = '0' else LO;

update : process(rst, clk)
begin

if rst=YES then
-- Asynchronous reset...
hAddr_r <= (others => '0');
hDEm3_r <= '0';
hDEm2_r <= '0';
hDEm1_r <= '0';
hDE_r <= '0';
vDEm1_r <= '0';
vDEm2_r <= '0';
vDE_r <= '0';
nlBurst_r <= '0';
IVEnA_r <= '0';
IVEnB_r <= '0';
IVSync_r <= '1';
IHSync_r <= '1';
hCount_r <= 0;
vCount_r <= 0;
AltLine_r <= '0';
RGB_r <= (others => '0');
-- elsif rising_edge(clk) then
elsif clk'event and clk='1' then
-- Ripple pipline display enable bits...
hDEm3_r <= hDEm3_x;
hDEm2_r <= hDEm3_r;
hDEm1_r <= hDEm2_r;
hDE_r <= hDEm1_r;
vDEm2_r <= vDEm2_x;
vDEm1_r <= vDEm2_r;
vDE_r <= vDEm1_r;
nlBurst_r <= nlBurst_x;
IVEnA_r <= IVEnA_x;
IVEnB_r <= IVEnB_x;
-- Syncs...
IHSync_r <= IHSync_x;
IVSync_r <= IVSync_x;
-- Video data/address...
hAddr_r <= hAddr_x; -- Update video RAM address
RGB_r <= RGB_x; -- Latch video data
-- Counters...
hCount_r <= hCount_x;
vCount_r <= vCount_x;
AltLine_r <= AltLine_x;
end if;

end process update;

end arch;

Thanks for your patience.

Regards,
Peter