what is a mailbox in digtial system

[syedshan]

Hi all

I want to know what does mailbox in digital system means...
I mean I have an IP and I am digging into it and I found to different interfaces for sending command out.

One is simple command and the other is mailbox, but I found no apparent difference between the two and hence am confused why different.
The following is the snippet for command interface

--command entity
port(
..
  --command interface
   clk_cmd                       :in  std_logic; --cmd_in and cmd_out are synchronous to this clock;
   out_cmd                       :out std_logic_vector(63 downto 0);
   out_cmd_val                   :out std_logic;
   in_cmd                        :in  std_logic_vector(63 downto 0);
   in_cmd_val                    :in  std_logic;
...
...
 --mailbox interface
   mbx_in_reg                    :in  std_logic_vector(31 downto 0);--value of the mailbox to send
   mbx_in_val                    :in  std_logic                    --pulse to indicate mailbox is valid
);

architecture ...
....
   if (out_cmd_val_sig='1') then
         out_cmd(31 downto 0) <=in_reg;
         out_cmd(59 downto 32)<=in_reg_addr_sig+start_addr;
         out_cmd(63 downto 60)<=cmd_rd_ack;
      elsif (mbx_in_val_sig='1' or mbx_received='1' ) then
         out_cmd(31 downto 0) <=mbx_in_reg;
         out_cmd(59 downto 32)<=start_addr;
         out_cmd(63 downto 60)<=(others=>'0');
      else
         out_cmd(63 downto 0)<=(others=>'0');
      end if;

where as in the top level module, the code that generate mail box register values is as follows...

status_proc: process(clk_reg )
begin
   if(rising_edge(clk_reg)) then
       if (burst_skipped ='1' and burst_skip_int_en='1') then
         --send a mailbox to indicate a burst was skipped
         mbx_in_reg <= x"02" & skip_counter;
         mbx_in_val <= '1';
       elsif (burst_done ='1' and burst_done_int_en='1') then
         --send a mailbox to indicate a burst was done
         mbx_in_reg <= x"01" & skip_counter;
         mbx_in_val <= '1';
      else
         mbx_in_reg <= mbx_in_reg;
         mbx_in_val <= '0';
      end if;
   end if;
end process;

 

[mrflibble]

https://www.asic-world.com/systemverilog/sema_mail_events2.html
**broken link removed**

Within the context of processing commands from command line I'd say you can for example have 3 sources for commands: telnet interface, rs232 interface and telepathy. All three interfaces accept incoming commands, and then put it in the mailbox. Then you have 1 single process that gets messages from the mailbox and processes them. And then presumably parses the commands and executes them.