// Copyright 2018 ETH Zurich and University of Bologna.
// Copyright and related rights are licensed under the Solderpad Hardware
// License, Version 0.51 (the “License”); you may not use this file except in
// compliance with the License. You may obtain a copy of the License at
// http://solderpad.org/licenses/SHL-0.51. Unless required by applicable law
// or agreed to in writing, software, hardware and materials distributed under
// this 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.
//
// Author: Florian Zaruba, ETH Zurich
// Date: 15/07/2017
// Description: A RISC-V privilege spec 1.11 (WIP) compatible CLINT (core local interrupt controller)
//
// Platforms provide a real-time counter, exposed as a memory-mapped machine-mode register, mtime. mtime must run at
// constant frequency, and the platform must provide a mechanism for determining the timebase of mtime (device tree).
module clint #(
parameter int unsigned AXI_ADDR_WIDTH = 64,
parameter int unsigned AXI_DATA_WIDTH = 64,
parameter int unsigned AXI_ID_WIDTH = 10,
parameter int unsigned NR_CORES = 1 // Number of cores therefore also the number of timecmp registers and timer interrupts
) (
input logic clk_i, // Clock
input logic rst_ni, // Asynchronous reset active low
input logic testmode_i,
input ariane_axi::req_t axi_req_i,
output ariane_axi::resp_t axi_resp_o,
input logic rtc_i, // Real-time clock in (usually 32.768 kHz)
output logic [NR_CORES-1:0] timer_irq_o, // Timer interrupts
output logic [NR_CORES-1:0] ipi_o // software interrupt (a.k.a inter-process-interrupt)
);
// register offset
localparam logic [15:0] MSIP_BASE = 16'h0;
localparam logic [15:0] MTIMECMP_BASE = 16'h4000;
localparam logic [15:0] MTIME_BASE = 16'hbff8;
localparam AddrSelWidth = (NR_CORES == 1) ? 1 : $clog2(NR_CORES);
// signals from AXI 4 Lite
logic [AXI_ADDR_WIDTH-1:0] address;
logic en;
logic we;
logic [63:0] wdata;
logic [63:0] rdata;
// bit 11 and 10 are determining the address offset
logic [15:0] register_address;
assign register_address = address[15:0];
// actual registers
logic [63:0] mtime_n, mtime_q;
logic [NR_CORES-1:0][63:0] mtimecmp_n, mtimecmp_q;
logic [NR_CORES-1:0] msip_n, msip_q;
// increase the timer
logic increase_timer;
// -----------------------------
// AXI Interface Logic
// -----------------------------
axi_lite_interface #(
.AXI_ADDR_WIDTH ( AXI_ADDR_WIDTH ),
.AXI_DATA_WIDTH ( AXI_DATA_WIDTH ),
.AXI_ID_WIDTH ( AXI_ID_WIDTH )
) axi_lite_interface_i (
.clk_i ( clk_i ),
.rst_ni ( rst_ni ),
.axi_req_i ( axi_req_i ),
.axi_resp_o ( axi_resp_o ),
.address_o ( address ),
.en_o ( en ),
.we_o ( we ),
.data_i ( rdata ),
.data_o ( wdata )
);
// -----------------------------
// Register Update Logic
// -----------------------------
// APB register write logic
always_comb begin
mtime_n = mtime_q;
mtimecmp_n = mtimecmp_q;
msip_n = msip_q;
// RTC says we should increase the timer
if (increase_timer)
mtime_n = mtime_q + 1;
// written from APB bus - gets priority
if (en && we) begin
case (register_address) inside
[MSIP_BASE:MSIP_BASE+8*NR_CORES]: begin
msip_n[$unsigned(address[AddrSelWidth-1+3:3])] = wdata[0];
end
[MTIMECMP_BASE:MTIMECMP_BASE+8*NR_CORES]: begin
mtimecmp_n[$unsigned(address[AddrSelWidth-1+3:3])] = wdata;
end
MTIME_BASE: begin
mtime_n = wdata;
end
default:;
endcase
end
end
// APB register read logic
always_comb begin
rdata = 'b0;
if (en && !we) begin
case (register_address) inside
[MSIP_BASE:MSIP_BASE+8*NR_CORES]: begin
rdata = msip_q[$unsigned(address[AddrSelWidth-1+3:3])];
end
[MTIMECMP_BASE:MTIMECMP_BASE+8*NR_CORES]: begin
rdata = mtimecmp_q[$unsigned(address[AddrSelWidth-1+3:3])];
end
MTIME_BASE: begin
rdata = mtime_q;
end
default:;
endcase
end
end
// -----------------------------
// IRQ Generation
// -----------------------------
// The mtime register has a 64-bit precision on all RV32, RV64, and RV128 systems. Platforms provide a 64-bit
// memory-mapped machine-mode timer compare register (mtimecmp), which causes a timer interrupt to be posted when the
// mtime register contains a value greater than or equal (mtime >= mtimecmp) to the value in the mtimecmp register.
// The interrupt remains posted until it is cleared by writing the mtimecmp register. The interrupt will only be taken
// if interrupts are enabled and the MTIE bit is set in the mie register.
always_comb begin : irq_gen
// check that the mtime cmp register is set to a meaningful value
for (int unsigned i = 0; i < NR_CORES; i++) begin
if (mtime_q >= mtimecmp_q[i]) begin
timer_irq_o[i] = 1'b1;
end else begin
timer_irq_o[i] = 1'b0;
end
end
end
// -----------------------------
// RTC time tracking facilities
// -----------------------------
// 1. Put the RTC input through a classic two stage edge-triggered synchronizer to filter out any
// metastability effects (or at least make them unlikely :-))
sync_wedge i_sync_edge (
.clk_i,
.rst_ni,
.en_i ( ~testmode_i ),
.serial_i ( rtc_i ),
.r_edge_o ( increase_timer ),
.f_edge_o ( ), // left open
.serial_o ( ) // left open
);
// Registers
always_ff @(posedge clk_i or negedge rst_ni) begin
if (~rst_ni) begin
mtime_q <= 64'b0;
mtimecmp_q <= 'b0;
msip_q <= '0;
end else begin
mtime_q <= mtime_n;
mtimecmp_q <= mtimecmp_n;
msip_q <= msip_n;
end
end
assign ipi_o = msip_q;
// -------------
// Assertions
// --------------
//pragma translate_off
`ifndef VERILATOR
// Static assertion check for appropriate bus width
initial begin
assert (AXI_DATA_WIDTH == 64) else $fatal("Timer needs to interface with a 64 bit bus, everything else is not supported");
end
`endif
//pragma translate_on
endmodule