Need help on LPM_ROM (Altera)

Amit wrote:

where does the address come to get mapped to address argument of the
mega function?!
Click to expand...
The address is something *you* have to supply from your vga controller.

A vga controller is little more than a handful of counters. The sync
signals are generated when the counters are within a certain range.

There's at least 2 steps involved in displaying text characters on a video
screen.

1. You compute a (text) screen memory address based on the H & V counters
output from your VGA controller, depending on your chosen sceen dimensions
and resolution.
This address is used to read a character code from video RAM. The
simplest solution would use dual-port RAM for video memory.

2. You compute a character ROM address based on the character code and
(possibly) the H & V counters output from your VGA controller.
This address is used to read a pixel value from character ROM.

When you start adding colour information, a 3rd step involves using the
abovementioned pixel value in a palette table lookup.

These operations have to be pipelined, so you need to take that into
account when you sync the final pixel value with the H/VSYNC signals - ie.
you need to delay them by a few clocks.

Regards,

--
Mark McDougall, Engineer
Virtual Logic Pty Ltd, <http://www.vl.com.au>
21-25 King St, Rockdale, 2216
Ph: +612-9599-3255 Fax: +612-9599-3266
 
On Mar 6, 2:02 am, Tricky <Trickyh...@gmail.com> wrote:
On Mar 6, 6:38 am, Amit <amit.ko...@gmail.com> wrote:





Hi group,

 I want to simulate VGA signals using VHDL and still working on a code
but currently I'm confused about LPM_ROM.

Now, in order to show a character I'm using an MIF file which is
assigned to LPM_ROM megafunction. Now, the thing I do NOT understand
is how does the LPM_ROM works?

LPM_ROM has some parameters that I have assigned required values to it
but it also has inputs and output as well. In the following LPM_ROM
what should be assigned to the address? (marked with ???)

instance_of_mf : lpm_rom

GENERIC MAP (
LPM_WIDTH               => 3,
LPM_WIDTHAD          => 10,
LPM_NUMWORDS     => 1024,
LPM_FILE                  => "single_character.mif",
LPM_ADDRESS_CONTROL=> "REGISTERED",
LPM_OUTDATA         => "REGISTERED",
LPM_HINT                 => "REGISTERED",
LPM_TYPE                => "REGISTERED",
INTENDED_DEVICE_FAMILY => "REGISTERED"
          )
PORT MAP (
address => ????,
inclock => clk25Mhz,
outclock => clk25Mhz,
q => q

The address will need to be a 10 bit signal to select which 3 bit word
you want to read out of the memory. This rom you have set up has 1024
words that are 3 bits long. You can only read 1 at a time.

I suggest you go an read up about memory and how it works.- Hide quoted text -

- Show quoted text -
Click to expand...
Hi Tricky,

Thanks for your response. Just to make it clear please know there are
two entities. "entity 1" will be embedded into the 2nd one. I'm using
LPM_ROM in the architecture of the 2nd. The problem is that I don't
see any address to map it to LPM_ROM address input.

where does the address come to get mapped to address argument of the
mega function?!

any advice is appreciated.


entity 1:
clock in std_logic
hsync and vsync out std_logic
pixel_row std_logic_vector(8 downto 0)
pixel_col std_logic_vector(9 downto 0 )

entity 2:
clock in std_logic
hsync out std_logic
vsync out std_logic
rgb out std_logic_vector(2 downto 0)
clk25 out std_logic and
Blank_n out std_logic
 
On Mar 6, 6:38 am, Amit <amit.ko...@gmail.com> wrote:
Hi group,

I want to simulate VGA signals using VHDL and still working on a code
but currently I'm confused about LPM_ROM.

Now, in order to show a character I'm using an MIF file which is
assigned to LPM_ROM megafunction. Now, the thing I do NOT understand
is how does the LPM_ROM works?

LPM_ROM has some parameters that I have assigned required values to it
but it also has inputs and output as well. In the following LPM_ROM
what should be assigned to the address? (marked with ???)

instance_of_mf : lpm_rom

GENERIC MAP (
LPM_WIDTH => 3,
LPM_WIDTHAD => 10,
LPM_NUMWORDS => 1024,
LPM_FILE => "single_character.mif",
LPM_ADDRESS_CONTROL=> "REGISTERED",
LPM_OUTDATA => "REGISTERED",
LPM_HINT => "REGISTERED",
LPM_TYPE => "REGISTERED",
INTENDED_DEVICE_FAMILY => "REGISTERED"
)
PORT MAP (
address => ????,
inclock => clk25Mhz,
outclock => clk25Mhz,
q => q
Click to expand...
The address will need to be a 10 bit signal to select which 3 bit word
you want to read out of the memory. This rom you have set up has 1024
words that are 3 bits long. You can only read 1 at a time.

I suggest you go an read up about memory and how it works.
 
A

Amit

Guest
Hi group,

I want to simulate VGA signals using VHDL and still working on a code
but currently I'm confused about LPM_ROM.


Now, in order to show a character I'm using an MIF file which is
assigned to LPM_ROM megafunction. Now, the thing I do NOT understand
is how does the LPM_ROM works?

LPM_ROM has some parameters that I have assigned required values to it
but it also has inputs and output as well. In the following LPM_ROM
what should be assigned to the address? (marked with ???)

instance_of_mf : lpm_rom

GENERIC MAP (
LPM_WIDTH => 3,
LPM_WIDTHAD => 10,
LPM_NUMWORDS => 1024,
LPM_FILE => "single_character.mif",
LPM_ADDRESS_CONTROL=> "REGISTERED",
LPM_OUTDATA => "REGISTERED",
LPM_HINT => "REGISTERED",
LPM_TYPE => "REGISTERED",
INTENDED_DEVICE_FAMILY => "REGISTERED"
)
PORT MAP (
address => ????,
inclock => clk25Mhz,
outclock => clk25Mhz,
q => q
 
On Mar 6, 7:00 pm, Mark McDougall <ma...@vl.com.au> wrote:
Amit wrote:
where does the address come to get mapped to address argument of the
mega function?!

The address is something *you* have to supply from your vga controller.

A vga controller is little more than a handful of counters. The sync
signals are generated when the counters are within a certain range.

There's at least 2 steps involved in displaying text characters on a video
screen.

1. You compute a (text) screen memory address based on the H & V counters
output from your VGA controller, depending on your chosen sceen dimensions
and resolution.
This address is used to read a character code from video RAM. The
simplest solution would use dual-port RAM for video memory.

2. You compute a character ROM address based on the character code and
(possibly) the H & V counters output from your VGA controller.
This address is used to read a pixel value from character ROM.

When you start adding colour information, a 3rd step involves using the
abovementioned pixel value in a palette table lookup.

These operations have to be pipelined, so you need to take that into
account when you sync the final pixel value with the H/VSYNC signals - ie.
you need to delay them by a few clocks.

Regards,

--
Mark McDougall, Engineer
Virtual Logic Pty Ltd, <http://www.vl.com.au
21-25 King St, Rockdale, 2216
Ph: +612-9599-3255 Fax: +612-9599-3266
Click to expand...

Thank you Mark for the details.

Regards,
Amit
 
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