Error in my VHDL code, but I can't seem to figure out why

Question

I wrote a VHDL code for the state diagram shown(augh, couldn't post the image because I'm a new user). However, when I compile it it says that there are errors: in line 16: process(clk) -- syntax error detected at the time of parsing line 21: else -- syntax error detected at the time of parsing line 23: end if; -- syntax error detected at the time of parsing.

This is my code:

library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.std_logic_arith.all;
use IEEE.std_logic_unsigned.ALL;
entity memory_controller is
port(clk: in std_logic;
 reset: in std_logic;
 bus_id: in std_logic_vector(7 downto 0);
 read_write, burst: in std_logic;
 oe, we, addr_1, addr_2: out std_logic
 );
end memory_controller;
architecture behavioral of memory_controller is
type statetype is (idle, decision, wr, rd1, rd2, rd3, rd4);
signal present_state, next_state : statetype;
process(clk) [LINE 16]
begin
if (rising_edge(clk)) then
    if (reset ='0') then
        present_state <= next_state;  
    else [LINE 21]
        present_state <= idle;   
    end if; [LINE 23]
end if;
end process;  
process(present_state, read_write, ready, burst)
begin
case present_state is
when idle => 
    oe => '0'; we=> '0'; addr_1=> '0'; addr_2=> '0';
if(bus_id = "11110011") then
    next_state <= decision;
else
    next_state <= idle;
end if;
when decision =>
    if (read_write = '1')
        then next_state <= rd1;
    else next_state <= wr;
end if;
when wr =>
we = '1';
    if (ready = '1')
then next_state <= idle;
else
next_state <= wr;
end if;
when rd1 =>
oe = '1';
addr_1 = addr_1 + '1';
addr_2 = addr_2 + '1';
if(ready = '0') then
next_state <= rd1;
if(burst = '0') then
next_state <= idle;
else next_state <= rd2;
end if;
when rd2 =>
oe = '1';
addr_1 = addr_1 + '1';
 addr_2 = addr_2 + '1';
if(ready = '1') then
next_state => rd3;
else
next_state => rd2;
end if;
when rd3 =>
oe = '1';
addr_1 = addr_1 + '1';
 addr_2 = addr_2 + '1';
if(ready = '1') then 
next_state => rd4;
else
next_state => rd3;
when rd4 =>
oe = '1';
addr_1 = addr_1 + '1';
addr_2 = addr_2 + '1';
if(ready = '1')
 then next_state => idle;
else next_state => rd4;
end if;
end case;
end process;
end behavioral;

The syntax is perfectly right, I don't understand why it's an error. What could be wrong?

Also, I want to use assert statements for cases when ready =0 , burst =0 and ready = 0 and burst = 1, but I'm not so sure as to how to implement them in the main code.

I have highlighted lines 16, 21 and 23.

Any help would be great.

Answer 1

The form of a VHDL module is typically:

entity MODULENAME is
  <Port description>
end MODULENAME;

architecture behavioral of MODULENAME is
  <signal declarations and similar>
begin
  <synchronous and combinatorial logic statements>
end architecture behavioral;

What you are lacking is the begin after your signal declarations. That is, change

architecture behavioral of memory_controller is
  type statetype is (idle, decision, wr, rd1, rd2, rd3, rd4);
  signal present_state, next_state : statetype;

  process(clk) [LINE 16]
  begin
    if (rising_edge(clk)) then

To:

architecture behavioral of memory_controller is
  type statetype is (idle, decision, wr, rd1, rd2, rd3, rd4);
  signal present_state, next_state : statetype;

begin

  process(clk) [LINE 16]
  begin
    if (rising_edge(clk)) then

Answer 2

As Sonicwave points out, you are missing the begin keyword before your first statement.

There are several more syntax errors. Signal assignments use a left-pointing arrow:

• not oe => '0'; but oe <= '0';
• not we = '1'; but we <= '1';

If you use an editor with direct compiler feedback, you'll save yourself a lot of time.