Add credit_counter (#225)

* Add credit_counter

Co-authored-by: Paul Scheffler <[email protected]>

* credit_counter: replace FFLARNC with FFARNC

Co-authored-by: Nils Wistoff <[email protected]>

---------

Co-authored-by: Paul Scheffler <[email protected]>
Co-authored-by: Nils Wistoff <[email protected]>

Bender.yml

@@ -32,6 +32,7 @@ sources:
       - src/cdc_reset_ctrlr_pkg.sv
       - src/cf_math_pkg.sv
       - src/clk_int_div.sv
+      - src/credit_counter.sv
       - src/delta_counter.sv
       - src/ecc_pkg.sv
       - src/edge_propagator_tx.sv

CHANGELOG.md

@@ -4,6 +4,10 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
+## Unreleased
+### Added
+- `credit_counter`: Add up/down counter for credit.
+
 ## 1.36.0 - 2024-07-08
 ### Fixed
 - `registers`: Fix else statement in FFARNC macro.

README.md

@@ -55,6 +55,7 @@ Please note that cells with status *deprecated* are not to be used for new desig
 | Name                | Description                                                       | Status       | Superseded By |
 | ------------------- | ----------------------------------------------------------------- | ------------ | ------------- |
 | `counter`           | Generic up/down counter with overflow detection                   | active       |               |
+| `credit_counter`    | Up/down counter for credit                                        | active       |               |
 | `delta_counter`     | Up/down counter with variable delta and overflow detection        | active       |               |
 | `generic_LFSR_8bit` | 8-bit linear feedback shift register (LFSR)                       | *deprecated* | `lfsr_8bit`   |
 | `lfsr_8bit`         | 8-bit linear feedback shift register (LFSR)                       | active       |               |

common_cells.core

@@ -16,6 +16,7 @@ filesets:
       - src/cc_onehot.sv
       - src/cf_math_pkg.sv
       - src/clk_int_div.sv
+      - src/credit_counter.sv
       - src/delta_counter.sv
       - src/ecc_pkg.sv
       - src/edge_propagator_tx.sv

src/credit_counter.sv

@@ -0,0 +1,55 @@
+// Copyright 2020 ETH Zurich and University of Bologna.
+// Solderpad Hardware License, Version 0.51, see LICENSE for details.
+// SPDX-License-Identifier: SHL-0.51
+
+// Author: Fabian Schuiki <[email protected]>
+// Author: Paul Scheffler <[email protected]>
+
+`include "common_cells/registers.svh"
+`include "common_cells/assertions.svh"
+
+module credit_counter #(
+  parameter int unsigned NumCredits      = 0,
+  /// Whether credit is full or empty on reset
+  parameter bit          InitCreditEmpty = 1'b0,
+  /// Derived parameters *Do not override*
+  parameter int unsigned InitNumCredits  = InitCreditEmpty ? '0 : NumCredits,
+  parameter type         credit_cnt_t    = logic [$clog2(NumCredits):0]
+) (
+  input  logic clk_i,
+  input  logic rst_ni,
+
+  output credit_cnt_t credit_o,
+
+  input  logic credit_give_i,
+  input  logic credit_take_i,
+  input  logic credit_init_i,  // Reinitialize (soft-reset) credit; takes priority
+
+  output logic credit_left_o,
+  output logic credit_crit_o,  // Giving one more credit will fill the credits
+  output logic credit_full_o
+);
+
+  credit_cnt_t credit_d, credit_q;
+  logic increment, decrement;
+
+  assign decrement = credit_take_i & ~credit_give_i;
+  assign increment = ~credit_take_i & credit_give_i;
+
+  always_comb begin
+    credit_d = credit_q;
+    if      (decrement) credit_d = credit_q - 1;
+    else if (increment) credit_d = credit_q + 1;
+  end
+
+  `FFARNC(credit_q, credit_d, credit_init_i, InitNumCredits, clk_i, rst_ni)
+
+  assign credit_o       = credit_q;
+  assign credit_left_o  = (credit_q != '0);
+  assign credit_crit_o  = (credit_q == NumCredits-1);
+  assign credit_full_o  = (credit_q == NumCredits);
+
+  `ASSERT_NEVER(CreditUnderflow, credit_o == '0 && decrement)
+  `ASSERT_NEVER(CreditOverflow, credit_o == NumCredits && increment)
+
+endmodule

src_files.yml

@@ -11,6 +11,7 @@ common_cells_all:
     - src/cc_onehot.sv
     - src/cf_math_pkg.sv
     - src/clk_int_div.sv
+    - src/credit_counter.sv
     - src/delta_counter.sv
     - src/ecc_pkg.sv
     - src/edge_propagator_tx.sv