rtl: add OBI timer

Author: ezelioli

rtl/obi_timer/obi_timer.sv

@@ -0,0 +1,110 @@
+module obi_timer #(
+  parameter type          obi_req_t = logic,
+  parameter type          obi_rsp_t = logic
+) (
+  input  logic     clk_i,
+  input  logic     rst_ni,
+  input  obi_req_t obi_req_i,
+  output obi_rsp_t obi_rsp_o,
+  output logic     expired_o,
+  output logic     overflow_o
+);
+
+  // Registers
+  logic [31:0]   count_d,   count_q;
+  logic [31:0] compare_d, compare_q;
+  logic         enable_d,  enable_q;
+
+  // Internal signals
+  obi_req_t      obi_req_d, obi_req_q;
+  logic              err_d,     err_q;
+  logic     [31:0] rdata_d,   rdata_q;
+
+  assign obi_req_d = obi_req_i;
+
+  // bit enable mask: defines which bits are written to by wdata of the OBI request
+  logic [31:0] be_mask;
+  for (genvar i = 0; unsigned'(i) < 32/8; ++i ) begin : gen_write_mask
+    assign be_mask[8*i +: 8] = {8{obi_req_i.a.be[i]}};
+  end
+
+  // Output assignment
+  assign expired_o  = (compare_q != 32'h0 && compare_q == count_q) ? 1'b1 1'b0;
+  assign overflow_o = (count_q == 32'hffff_ffff) ? 1'b1 : 1'b0;
+
+  always_comb begin : obi_response
+    obi_rsp_o         = '0;
+    obi_rsp_o.gnt     = 1'b1; 
+    obi_rsp_o.rvalid  = obi_req_q.req;
+    obi_rsp_o.r.err   = err_q;
+    obi_rsp_o.r.rid   = obi_req_q.a.aid;
+    obi_rsp_o.r.rdata = rdata_q;
+  end
+
+  always_comb begin
+    err_d     = '0;
+    rdata_d   = '0;
+    count_d   = count_q;
+    compare_d = compare_q;
+    enable_d  = enable_q;
+
+    if (expired_o)
+      count_d = '0;
+    else if (enable_q)
+      count_d = count_q + 1;
+
+    if (obi_req_i.req) begin
+
+      if (obi_req_i.a.we) begin : write
+        automatic logic [31:0] wdata = obi_req_i.a.wdata & be_mask;
+        unique case ({obi_req_i.a.addr[IntAddrWidth-1:2], 2'b00})
+          OBI_TIMER_COUNT_OFFSET: begin
+            count_d = wdata;
+          end
+          OBI_TIMER_COMPARE_OFFSET: begin
+            compare_d = wdata;
+            count_d   = '0;
+          end
+          OBI_TIMER_ENABLE_OFFSET: begin
+            enable_d = wdata[0];
+          end
+          default: begin
+            err_d = 1'b1;
+          end
+        endcase
+
+      end else begin : read
+        unique case ({obi_req_i.a.addr[IntAddrWidth-1:2], 2'b00})
+          OBI_TIMER_COUNT_OFFSET: begin
+            rdata_d = count_q;
+          end
+          OBI_TIMER_COMPARE_OFFSET: begin
+            rdata_d = compare_q;
+          end
+          OBI_TIMER_ENABLE_OFFSET: begin
+            rdata_d = {31'h0, enable_q};
+          end
+          default: begin
+            rdata_d = 32'hBADCAB1E;
+            err_d   = 1'b1;
+          end
+        endcase
+      end
+
+    end
+  end
+
+  always_ff @(posedge clk_i or negedge rst_ni) begin
+    if (~rst_ni) begin
+      count_q   <= '0;
+      compare_q <= '0;
+      enable_q  <= '0;
+    end else begin
+      count_q   <= count_d;
+      compare_q <= compare_d;
+      enable_q  <= enable_d;
+    end
+  end
+
+
+endmodule

rtl/obi_timer/obi_timer_pkg.sv

@@ -0,0 +1,12 @@
+package obi_timer_pkg;
+
+  // Internal address width. We only need 4 bits to
+  // store the offsets of the three registers implemented.
+  localparam int unsigned IntAddrWidth = 5;
+
+  // Register offsets
+  parameter logic [IntAddrWidth-1:0] OBI_TIMER_COUNT_OFFSET    = 4'h0;
+  parameter logic [IntAddrWidth-1:0] OBI_TIMER_COMPARE_OFFSET  = 4'h4;
+  parameter logic [IntAddrWidth-1:0] OBI_TIMER_ENABLE_OFFSET   = 4'h8;
+
+endpackage