Entity: fifo_cc_got_tempgot

Diagram

positive D_BITS positive MIN_DEPTH boolean DATA_REG boolean STATE_REG boolean OUTPUT_REG natural ESTATE_WR_BITS natural FSTATE_RD_BITS std_logic rst std_logic clk std_logic put std_logic_vector(D_BITS-1 downto 0) din std_logic got std_logic commit std_logic rollback std_logic full std_logic_vector(imax(0, ESTATE_WR_BITS-1) downto 0) estate_wr std_logic_vector(D_BITS-1 downto 0) dout std_logic valid std_logic_vector(imax(0, FSTATE_RD_BITS-1) downto 0) fstate_rd

Description

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Authors: Thomas B. Preusser Steffen Koehler Martin Zabel Patrick Lehmann

Entity: FIFO, common clock (cc), pipelined interface, reads only become effective after explicit commit

Description:

The specified depth (MIN_DEPTH) is rounded up to the next suitable value.

As uncommitted reads occupy FIFO space that is not yet available for writing, an instance of this FIFO can, indeed, report full and not vld at the same time. While a commit would eventually make space available for writing (not ful), a rollback would re-iterate data for reading (vld).

commit and rollback are inclusive and apply to all reads (got) since the previous commit or rollback up to and including a potentially simultaneous read.

The FIFO state upon a simultaneous assertion of commit and rollback is undefined!

*STATE_*_BITS defines the granularity of the fill state indicator *state_*. fstate_rd is associated with the read clock domain and outputs the guaranteed number of words available in the FIFO. estate_wr is associated with the write clock domain and outputs the number of words that is guaranteed to be accepted by the FIFO without a capacity overflow. Note that both these indicators cannot replace the full or valid outputs as they may be implemented as giving pessimistic bounds that are minimally off the true fill state.

If a fill state is not of interest, set *STATE_*_BITS = 0.

fstate_rd and estate_wr are combinatorial outputs and include an address comparator (subtractor) in their path.

Examples:

  • FSTATE_RD_BITS = 1:

    • fstate_rd == 0 => 0/2 full
    • fstate_rd == 1 => 1/2 full (half full)

  • FSTATE_RD_BITS = 2:

    • fstate_rd == 0 => 0/4 full
    • fstate_rd == 1 => 1/4 full
    • fstate_rd == 2 => 2/4 full
    • fstate_rd == 3 => 3/4 full

License:

Copyright 2007-2014 Technische Universitaet Dresden - Germany, Chair of VLSI-Design, Diagnostics and Architecture

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and

limitations under the License.

Generics

Generic name Type Value Description
D_BITS positive Data Width
MIN_DEPTH positive Minimum FIFO Depth
DATA_REG boolean false Store Data Content in Registers
STATE_REG boolean false Registered Full/Empty Indicators
OUTPUT_REG boolean false Registered FIFO Output
ESTATE_WR_BITS natural 0 Empty State Bits
FSTATE_RD_BITS natural 0 Full State Bits

Ports

Port name Direction Type Description
rst in std_logic Global Reset and Clock
clk in std_logic Global Reset and Clock
put in std_logic Write Request
din in std_logic_vector(D_BITS-1 downto 0) Input Data
full out std_logic
estate_wr out std_logic_vector(imax(0, ESTATE_WR_BITS-1) downto 0)
got in std_logic Read Completed
dout out std_logic_vector(D_BITS-1 downto 0) Output Data
valid out std_logic
fstate_rd out std_logic_vector(imax(0, FSTATE_RD_BITS-1) downto 0)
commit in std_logic
rollback in std_logic

Signals

Name Type Description
IP0 unsigned(A_BITS-1 downto 0) --------------------------------------------------------------------------- Memory Pointers Actual Input and Output Pointers
OP0 unsigned(A_BITS-1 downto 0)
IP1 unsigned(A_BITS-1 downto 0) Incremented Input and Output Pointers
OP1 unsigned(A_BITS-1 downto 0)
OPm unsigned(A_BITS-1 downto 0) Committed Read Pointer (Commit Marker)
wa unsigned(A_BITS-1 downto 0) --------------------------------------------------------------------------- Backing Memory Connectivity Write Port
we std_logic
ra unsigned(A_BITS-1 downto 0) Read Port
re std_logic
fulli std_logic Internal full and empty indicators
empti std_logic

Constants

Name Type Value Description
A_BITS natural log2ceil(MIN_DEPTH)
FORCE_XILCY boolean (not SIMULATION) and (VENDOR = VENDOR_XILINX) and STATE_REG and (A_BITS > 4) Force Carry-Chain Use for Pointer Increments on Xilinx Architectures

Processes

Description
Fill State Computation (soft indicators)