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library ieee;
use ieee.std_logic_1164.all;
package QueueP is
generic (
type QUEUE_TYPE;
function to_string(d : in QUEUE_TYPE) return string
);
-- simple queue interface
type t_simple_queue is protected
procedure push (data : in QUEUE_TYPE);
procedure pop (data : out QUEUE_TYPE);
impure function is_empty return boolean;
impure function is_full return boolean;
end protected t_simple_queue;
end package QueueP;
package body QueueP is
-- simple queue implementation
-- inspired by noasic article http://noasic.com/blog/a-simple-fifo-using-vhdl-protected-types/
type t_simple_queue is protected body
constant C_QUEUE_DEPTH : natural := 64;
type t_queue_array is array (0 to C_QUEUE_DEPTH-1) of QUEUE_TYPE;
variable v_queue : t_queue_array;
variable v_count : natural range 0 to t_queue_array'length := 0;
variable v_head : natural range 0 to t_queue_array'high := 0;
variable v_tail : natural range 0 to t_queue_array'high := 0;
-- write one entry into queue
procedure push (data : in QUEUE_TYPE) is
begin
assert not(is_full)
report "push into full queue -> discarded"
severity failure;
v_queue(v_head) := data;
v_head := (v_head + 1) mod t_queue_array'length;
v_count := v_count + 1;
end procedure push;
-- read one entry from queue
procedure pop (data : out QUEUE_TYPE) is
begin
assert not(is_empty)
report "pop from empty queue -> discarded"
severity failure;
data := v_queue(v_tail);
v_tail := (v_tail + 1) mod t_queue_array'length;
v_count := v_count - 1;
end procedure pop;
-- returns true if queue is empty, false otherwise
impure function is_empty return boolean is
begin
return v_count = 0;
end function is_empty;
-- returns true if queue is full, false otherwise
impure function is_full return boolean is
begin
return v_count = t_queue_array'length;
end function is_full;
end protected body t_simple_queue;
end package body QueueP;
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