pci_arb.vhd

sparc org, vhdl rtl code

----------------------------------------------------------------------------
--  This file is a part of the LEON VHDL model
--  Copyright (C) 1999  European Space Agency (ESA)
--
--  This library is free software; you can redistribute it and/or
--  modify it under the terms of the GNU Lesser General Public
--  License as published by the Free Software Foundation; either
--  version 2 of the License, or (at your option) any later version.
--
--  See the file COPYING.LGPL for the full details of the license.


--============================================================================--
-- Design unit  : pci_arb
--
-- File name    : pci_arb.vhd
--
-- Purpose      : Arbiter for the PCI bus
--                - configurable size: 4, 8, 16, 32 agents
--                - nested round-robbing in two different priority levels
--                - priority assignment hard-coded or APB-programmable
--
-- Reference    : PCI Local Bus Specification, Revision 2.1,
--                PCI Special Interest Group, 1st June 1995
--                (for information: http: 
-- Reference    : AMBA(TM) Specification (Rev 2.0), ARM IHI 0011A,
--                13th May 1999, issue A, first release, ARM Limited
--                The document can be retrieved from http: 
--
-- Note         : Numbering for req_n, gnt_n, or priority levels is in
--                increasing order <0 = left> to <NUMBER-1 = right>.
--                APB data/address arrays are in the conventional order: 
--                The least significant bit is located to the
--                right, carrying the lower index number (usually 0).
--                The arbiter considers strong signal levels ('1' and '0')
--                only. Weak levels ('H', 'L') are not considered. The
--                appropriate translation function (to_X01) must be applied
--                to the inputs. This is usually done by the pads,
--                and therefore not contained in this model.
--                
-- Configuration: The arbiter can be configured to NB_AGENTS = 4, 8, 16 or 32.
--                A priority level (0 = high, 1 = low) is assigned to each device.
--                Exception is agent NB_AGENTS-1, which has always lowest priority.
--
--                a) The priority levels are hard-coded, when APB_PRIOS = false.
--                In this case, the APB ports (pbi/pbo) are unconnected.
--                The constant ARB_LVL_C must then be set to appropriate values.
--
--                b) When APB_PRIOS = true, the levels are programmable via the
--                APB-address 0x80 (allows to be ored with the PCI interface):
--                Bit 31 (leftmost) = master 31 . . bit 0 (rightmost) = master 0.
--                Bit NB_AGENTS-1 is dont care at write and reads 1.
--                Bits NB_AGENTS to 31, if existing, are dont care and read 0.
--                The constant ARB_LVL_C is then the reset value.
--                
-- Algorithm    : The algorithm is described in the implementation note of
--                section 3.4 of the PCI standard:
--                The bus is granted by two nested round-robbing loops.
--                An agent number and a priority level is assigned to each agent.
--                The agent number determines, the pair of req_n/gnt_n lines.
--                Agents are counted from 0 to NB_AGENTS-1.
--                All agents in one level have equal access to the bus
--                (round-robbing); all agents of level 1 as a group have access
--                equal to each agent of level 0.
--                Re-arbitration occurs, when frame_n is asserted, as soon
--                as any other master has requested the bus, but only
--                once per transaction.
--                
--                b) With programmable priorities. The priority level of all
--                   agents (except NB_AGENTS-1) is  programmable via APB.
--                   In a 256 byte APB address range, the priority level of
--                   agent N is accessed via the address 0x80 + 4*N. The APB
--                   slave returns 0 on all non-implemented addresses, the
--                   address bits (1:0) are not decoded. Since only addresses
--                   >= 0x80 are occupied, it can be used in parallel (ored
--                   read data) with our PCI interface (uses <= 0x78).
--                   The constant ARB_LVL_C in pci_arb_pkg is the reset value.
--
-- Timeout:       The "broken master" timeout is another reason for
--                re-arbitration (section 3.4.1 of the standard). Grant is
--                removed from an agent, which has not started a cycle
--                within 16 cycles after request (and grant). Reporting of
--                such a 'broken' master is not implemented.
--
-- Turnover:      A turnover cycle is required by the standard, when re-
--                arbitration occurs during idle state of the bus.
--                Notwithstanding to the standard, "idle state" is assumed,
--                when frame_n is high for more than 1 cycle.
--
-- Bus parking  : The bus is parked to agent 0 after reset, it remains granted
--                to the last owner, if no other agent requests the bus.
--                When another request is asserted, re-arbitration occurs
--                after one turnover cycle.
--
-- Lock         : Lock is defined as a resource lock by the PCI standard.
--                The optional bus lock mentioned in the standard is not
--                considered here and there are no special conditions to
--                handle when lock_n is active.
--                in arbitration.
--
-- Latency      : Latency control in PCI is via the latency counters of each
--                agent. The arbiter does not perform any latency check and
--                a once granted agent continues its transaction until its
--                grant is removed AND its own latency counter has expired.
--                Even though, a bus re-arbitration occurs during a
--                transaction, the hand-over only becomes effective,
--                when the current owner deasserts frame_n.
--
-- Limitations  : [add here known bugs and limitations]
-- 
-- Library      : work
--
-- Dependencies : LEON config package
--                package amba, can be retrieved from:
--                http: 
--
-- Author       : Roland Weigand  <[e-mail]>
--                European Space Agency (ESA)
--                Microelectronics Section (TOS-ESM)
--                P.O. Box 299
--                NL-2200 AG Noordwijk ZH
--                The Netherlands
--
-- Contact      : mailto:[e-mail]
--                http: 

-- Copyright (C): European Space Agency (ESA) 2002. 
--                This source code is free software; you can redistribute it 
--                and/or modify it under the terms of the GNU Lesser General 
--                Public License as published by the Free Software Foundation; 
--                either version 2 of the License, or (at your option) any 
--                later version. For full details of the license see file
--                http: 
--
--                It is recommended that any use of this VHDL source code is
--                reported to the European Space Agency. It is also recommended 
--                that any use of the VHDL source code properly acknowledges the 
--                European Space Agency as originator. 

-- Disclaimer   : All information is provided "as is", there is no warranty that
--                the information is correct or suitable for any purpose,
--                neither implicit nor explicit. This information does not
--                necessarily reflect the policy of the European Space Agency.
--
-- Simulator    : Modelsim 5.5e on Linux RedHat 7.2
--
-- Synthesis    : Synopsys Version 1999.10 on Sparc + Solaris 5.5.1
-- 
--------------------------------------------------------------------------------
-- Version  Author   Date       Changes
--
-- 0.0      R. W.    2000/11/02 File created
-- 0.1      J.Gaisler     2001/04/10   Integrated in LEON
-- 0.2      R. Weigand    2001/04/25   Connect arb_lvl reg to AMBA clock/reset
-- 0.3      R. Weigand    2002/03/19   Default assignment to owneri in find_next
-- 1.0      RW.           2002/04/08   Implementation of TMR registers
--                                     Removed recursive function call
--                                     Fixed ARB_LEVELS = 2
-- 3.0      R. Weigand    2002/04/16   Released for leon2
-- $Log$
-- Revision 3.1  2002/07/31 13:22:09  weigand
-- Bugfix for cases where no valid request in level 0 (level 1 was not rearbitrated)
--
-- Revision 3.0  2002/07/24 12:19:38  weigand
-- Installed RCS with version 3.0
--
--------------------------------------------------------------------------------
library IEEE;
use IEEE.std_logic_1164.all;
-- use IEEE.std_logic_arith.all;
use work.leon_config.all;
package pci_arb_pkg is
   -- The following constants are defined by the target/device/config packages:
   -- The number of agents can be only 4, 8, 16, 32
   -- constant NB_AGENTS : natural range 3 to 32 := 4; -- Nb. of agents (4, 8, 16, 32)
   -- constant ARB_SIZE : natural range 2 to 5 := 2;  -- round up log2(NB_AGENTS) 
   -- constant APB_PRIOS : boolean := true;  -- levels programmable via APB

   subtype agent_t is std_logic_vector(ARB_SIZE-1 downto 0);
   subtype arb_lvl_t is std_logic_vector(NB_AGENTS-1 downto 0);
   subtype agentno_t is integer range 0 to NB_AGENTS-1;

   -- Note: the agent with the highest index (3, 7, 15, 31) is always in level 1
   -- Example: x010 = prio 0 for agent 2 and 0, prio 1 for agent 3 and 1.
   -- Default: start with all devices equal priority at level 1.
   constant ARB_LVL_C : arb_lvl_t := (others => '1');

   constant all_ones : std_logic_vector(0 to NB_AGENTS-1) := (others => '1');

end pci_arb_pkg;

library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.std_logic_unsigned."+";
use IEEE.std_logic_unsigned.conv_integer;
use IEEE.std_logic_arith.conv_unsigned;
use work.pci_arb_pkg.all;
use work.leon_config.all;
use work.amba.all;
use work.leon_iface.all;

entity pci_arb is
   
   port (clk     : in  clk_type;                            -- clock
         rst_n   : in  std_logic;                           -- async reset active low
         req_n   : in  std_logic_vector(0 to NB_AGENTS-1);  -- bus request
         frame_n : in  std_logic;
         gnt_n   : out std_logic_vector(0 to NB_AGENTS-1);  -- bus grant
         pclk    : in  clk_type;                            -- APB clock
         prst_n  : in  std_logic;                           -- APB reset