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Altera_Forum
Honored Contributor I
2,670 Views

Replacing a process with 1-port RAM

i have process I need to now implement as ROM.  

 

process (count, outi, run) --converter begin if (run = '1') then -- run is a physical switch case count is -- count is the current value of a 2 bit counter when "00" => outi <= "1000"; when "01" => outi <= "0100"; when "10" => outi <= "0001"; when "11" => outi <= "0010"; when others => outi <= "0000"; end case; end if; end process;  

 

The output outi is assigned to LEDS outside the process. 

 

I have created 1 port ram and created a mif file that looks like this 

 

 

Addr 

+0 

+1 

+2 

+3 

ASCII 

 

 

1000 

0100 

0001 

0010 

... 

 

 

 

But I'm not sure what exactly I need to do now.  

I'm very to new to VHDL and FPGAs in general.
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21 Replies
Altera_Forum
Honored Contributor I
141 Views

The question is, what is wrong with the current decoder? 

What code have you written already, and what are the end goals? For a ROM you have a few options: 

1. Use a wizard generated ROM, initialise with a .mif file 

2. Define a constant and then follow the ROM template (available in the HDL coding guidelines of the Quartus Manual - and/or you can generate the template in Quartus) 

3. Keep with the decoder structure, but add a clock. 

 

What do you need us to help with?
Altera_Forum
Honored Contributor I
141 Views

If indeed you want to use the 1-port RAM as a ROM, you'd need to remove your decoder logic (the case statement) and instantiate the RAM in your design, attaching count to the address input of the RAM and outi to the output of the RAM.

Altera_Forum
Honored Contributor I
141 Views

 

--- Quote Start ---  

If indeed you want to use the 1-port RAM as a ROM, you'd need to remove your decoder logic (the case statement) and instantiate the RAM in your design, attaching count to the address input of the RAM and outi to the output of the RAM. 

--- Quote End ---  

 

 

You can infer a ROM from decoder logic, if it is clocked.  

See "inferring ROM" from the Quartus HDL coding guidelines
Altera_Forum
Honored Contributor I
141 Views

 

--- Quote Start ---  

If indeed you want to use the 1-port RAM as a ROM, you'd need to remove your decoder logic (the case statement) and instantiate the RAM in your design, attaching count to the address input of the RAM and outi to the output of the RAM. 

--- Quote End ---  

 

 

sorry for really late reply. i forgot oops. 

I have actually done that with block diagrams but I want to do it using only vhdl now I just don't know how I'd go about doing that
Altera_Forum
Honored Contributor I
141 Views

 

--- Quote Start ---  

sorry for really late reply. i forgot oops. 

I have actually done that with block diagrams but I want to do it using only vhdl now I just don't know how I'd go about doing that 

--- Quote End ---  

 

 

Have you read the quartus handbook, the section on HDL coding guidelines? 

https://www.altera.com/en_us/pdfs/literature/hb/qts/qts-qps-handbook.pdf 

 

Specifically, Page 12-27 - Inferring ROM Functions from HDL Code
Altera_Forum
Honored Contributor I
141 Views

I read part of it a while ago, guess i forgot about. 

I found this --http://www.alteraforum.com/forum/showthread.php?t=5958--  

all I actually needed to do was use component instantiation and port map to connect the ROM to the main file.  

 

Thank you for your help.
Altera_Forum
Honored Contributor I
141 Views

I'm not sure if this is allowed but I have a problem with simulation. 

https://www.alteraforum.com/forum/attachment.php?attachmentid=13657  

 

The overall output of the entire program works but I want to see the internals. 

I get Us when I run a simulation for example I'm expecting the same output for "step" as "ROM:U1|address" 

U1 is a 1-port RAM that I instantiated and implemented as "ROM".
Altera_Forum
Honored Contributor I
141 Views

Without seeing the code, it is impossible to say what is wrong.

Altera_Forum
Honored Contributor I
141 Views

 

--- Quote Start ---  

Without seeing the code, it is impossible to say what is wrong. 

--- Quote End ---  

 

library IEEE; use IEEE.STD_LOGIC_1164.ALL; use IEEE.STD_LOGIC_UNSIGNED.ALL; entity school is Port ( CLOCK_50 : in std_logic; run : in std_logic; dir : in std_logic; step : out std_logic_vector (1 downto 0); led : out std_logic_vector(3 downto 0); slow_fast : in std_logic ); end school; architecture Behavioral of school is signal divider : std_logic_vector (22 downto 0); signal count : std_logic_vector (1 downto 0); signal current_clk : std_logic; component ROM IS PORT ( address : IN STD_LOGIC_VECTOR (1 DOWNTO 0); clock : IN STD_LOGIC := '1'; data : IN STD_LOGIC_VECTOR (3 DOWNTO 0); wren : IN STD_LOGIC ; q : OUT STD_LOGIC_VECTOR (3 DOWNTO 0) ); END component; begin U1 : ROM PORT MAP ( clock => current_clk, address => count, q => led, wren => '0', data => "0000" ); process (divider, CLOCK_50) begin if rising_edge(CLOCK_50) then divider <= divider + 1; end if; end process; process (run, divider, current_clk, dir, count, slow_fast ) begin if slow_fast = '1' then current_clk <= divider(0); else current_clk <= divider(1); end if; if (rising_edge(current_clk) and run = '1') then -- case dir is when '0' => count <= count + 1; when '1' => count <= count - 1; when others => count <= count + 1; end case; end if; end process; step <= count; end Behavioral;
Altera_Forum
Honored Contributor I
141 Views

Count doesnt have an initial value, or a reset value, hence it will initialise (in simulation) to 'U' 

 

You also have other issues: 

1. You should create logic divided clocks- they are prone to timing issues on hardware 

2/ do not use "and" with the clock 

3. its better to separate asynchronous and synchronous logic into different processes.
Altera_Forum
Honored Contributor I
141 Views

 

--- Quote Start ---  

Count doesnt have an initial value, or a reset value, hence it will initialise (in simulation) to 'U' 

 

You also have other issues: 

1. You should create logic divided clocks- they are prone to timing issues on hardware 

2/ do not use "and" with the clock 

3. its better to separate asynchronous and synchronous logic into different processes. 

--- Quote End ---  

 

 

I changed count to now be  

 

signal count : std_logic_vector (1 downto 0) :="00"; 

 

1. I'm sure what logic divided clock means. 

2. I changed it and used if conditions instead. 

3. I've done that also 

 

The output is still U for all of the U1 signals after running sim and count still initialises as U
Altera_Forum
Honored Contributor I
141 Views

Your "current_clk" is a logic generated clock, because you used logic to generate a clock 

Much better to use clock enables instead.
Altera_Forum
Honored Contributor I
141 Views

I made two process for different frequencies now the output looks time shifted but I don't really care about that for no. I still can't see any of U1's signals, they're all still U or UU or UUUU. is it that its just not possible or something?

Altera_Forum
Honored Contributor I
141 Views

Did you set and initial value for count? or reset it?

Altera_Forum
Honored Contributor I
141 Views

yeah signal count : std_logic_vector (1 downto 0) :="00";

Altera_Forum
Honored Contributor I
141 Views

And where is the testbench code? have you tried testing in modelsim?

Altera_Forum
Honored Contributor I
141 Views

 

--- Quote Start ---  

And where is the testbench code? have you tried testing in modelsim? 

--- Quote End ---  

 

I just made this  

 

library IEEE; use IEEE.STD_LOGIC_1164.ALL; use IEEE.STD_LOGIC_UNSIGNED.ALL; entity test is end test; architecture Behavioral of test is component tet is Port ( CLOCK_50 : in std_logic; run : in std_logic; dir : in std_logic; step : out std_logic_vector (1 downto 0); led : out std_logic_vector(3 downto 0):="1000"; slow_fast : in std_logic ); end component; signal run_a : std_logic := '1'; signal clk_a : std_logic := '0'; signal dir_a : std_logic := '1'; signal slow_a : std_logic := '0'; constant clkp : time := 20ps; signal step_a : std_logic_vector (1 downto 0); signal led_a : std_logic_vector (3 downto 0); begin A1 : tet port map (clk_a, run_a, dir_a, step_a, led_a, slow_a ); clk_proc : process begin clk_a <= '0'; wait for clkp/2; clk_a <= '1'; wait for clkp/2; end process; stim_proc: process begin wait for 20 ps; run_a <='1'; dir_a <= '1'; slow_a <= '0'; wait for 300 ps; run_a <='0'; wait for 300 ps; run_a <= '1'; dir_a <= '0'; wait for 300 ps; slow_a <= '1'; wait for 300 ps; end process; end Behavioral;  

 

step and led show up as "UU" and "UUUU" but the signal assignments work. 

But if i use the university program simulation, the main program works fine (apart from the Us I get for the ROM)
Altera_Forum
Honored Contributor I
141 Views

Did you assign any values to the rom? without specifying the contents, it will simulate with all U

Altera_Forum
Honored Contributor I
141 Views

 

--- Quote Start ---  

Did you assign any values to the rom? without specifying the contents, it will simulate with all U 

--- Quote End ---  

 

yeah i did. It was in my first post
Altera_Forum
Honored Contributor I
48 Views

You first post shows code that would infer a rom from code. The later code shows a component called "rom" with no port called "count"  

 

Please post ALL of your code. Why not post the project?
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