Made a number of modifications to the counter-timer to correctly pipeline
the 64-bit counter, including synchronizing the enables. There are still
two issues, one of which causes the testbench to fail, which have not been
solved.
diff --git a/verilog/rtl/counter_timer_low.v b/verilog/rtl/counter_timer_low.v
new file mode 100755
index 0000000..66989d2
--- /dev/null
+++ b/verilog/rtl/counter_timer_low.v
@@ -0,0 +1,309 @@
+/* Simple 32-bit counter-timer for Caravel. */
+
+/* Counter acts as low 32 bits of a 64-bit counter
+ * when chained with the other counter.
+ */
+
+module counter_timer_low_wb # (
+ parameter BASE_ADR = 32'h2400_0000,
+ parameter CONFIG = 8'h00,
+ parameter VALUE = 8'h04,
+ parameter DATA = 8'h08
+) (
+ input wb_clk_i,
+ input wb_rst_i,
+ input [31:0] wb_adr_i,
+ input [31:0] wb_dat_i,
+ input [3:0] wb_sel_i,
+ input wb_we_i,
+ input wb_cyc_i,
+ input wb_stb_i,
+
+ output wb_ack_o,
+ output [31:0] wb_dat_o,
+
+ input stop_in,
+ input enable_in,
+ output strobe,
+ output is_offset,
+ output stop_out,
+ output enable_out,
+ output irq
+);
+ wire [31:0] counter_timer_reg_cfg_do;
+ wire [31:0] counter_timer_reg_val_do;
+ wire [31:0] counter_timer_reg_dat_do;
+
+ wire resetn = ~wb_rst_i;
+ wire valid = wb_stb_i && wb_cyc_i;
+ wire counter_timer_reg_cfg_sel = valid && (wb_adr_i == (BASE_ADR | CONFIG));
+ wire counter_timer_reg_val_sel = valid && (wb_adr_i == (BASE_ADR | VALUE));
+ wire counter_timer_reg_dat_sel = valid && (wb_adr_i == (BASE_ADR | DATA));
+
+ wire reg_cfg_we = (counter_timer_reg_cfg_sel) ?
+ (wb_sel_i[0] & {wb_we_i}): 1'b0;
+ wire [3:0] reg_val_we = (counter_timer_reg_val_sel) ?
+ (wb_sel_i & {4{wb_we_i}}): 4'b0000;
+ wire [3:0] reg_dat_we = (counter_timer_reg_dat_sel) ?
+ (wb_sel_i & {4{wb_we_i}}): 4'b0000;
+
+ wire [31:0] mem_wdata = wb_dat_i;
+ wire reg_dat_re = counter_timer_reg_dat_sel && !wb_sel_i && ~wb_we_i;
+
+ assign wb_dat_o = (counter_timer_reg_cfg_sel) ? counter_timer_reg_cfg_do :
+ (counter_timer_reg_val_sel) ? counter_timer_reg_val_do :
+ counter_timer_reg_dat_do;
+ assign wb_ack_o = counter_timer_reg_cfg_sel || counter_timer_reg_val_sel ||
+ counter_timer_reg_dat_sel;
+
+ counter_timer_low counter_timer_low_inst (
+ .resetn(resetn),
+ .clkin(wb_clk_i),
+ .reg_val_we(reg_val_we),
+ .reg_val_di(mem_wdata),
+ .reg_val_do(counter_timer_reg_val_do),
+ .reg_cfg_we(reg_cfg_we),
+ .reg_cfg_di(mem_wdata),
+ .reg_cfg_do(counter_timer_reg_cfg_do),
+ .reg_dat_we(reg_dat_we),
+ .reg_dat_di(mem_wdata),
+ .reg_dat_do(counter_timer_reg_dat_do),
+ .stop_in(stop_in),
+ .strobe(strobe),
+ .is_offset(is_offset),
+ .enable_in(enable_in),
+ .stop_out(stop_out),
+ .enable_out(enable_out),
+ .irq_out(irq)
+ );
+
+endmodule
+
+module counter_timer_low (
+ input resetn,
+ input clkin,
+
+ input [3:0] reg_val_we,
+ input [31:0] reg_val_di,
+ output [31:0] reg_val_do,
+
+ input reg_cfg_we,
+ input [31:0] reg_cfg_di,
+ output [31:0] reg_cfg_do,
+
+ input [3:0] reg_dat_we,
+ input [31:0] reg_dat_di,
+ output [31:0] reg_dat_do,
+
+ input stop_in,
+ input enable_in,
+ output strobe,
+ output enable_out,
+ output stop_out,
+ output is_offset,
+ output irq_out
+);
+
+reg [31:0] value_cur;
+reg [31:0] value_reset;
+reg irq_out;
+wire stop_in; // High 32 bits counter has stopped
+reg strobe; // Strobe to high 32 bits counter; occurs
+ // one cycle before actual timeout and
+ // irq signal.
+reg stop_out; // Stop condition flag
+
+wire [31:0] value_cur_plus; // Next value, on up-count
+wire [31:0] value_cur_minus; // Next value, on down-count
+wire is_offset;
+
+reg enable; // Enable (start) the counter/timer
+reg lastenable; // Previous state of enable (catch rising/falling edge)
+reg oneshot; // Set oneshot (1) mode or continuous (0) mode
+reg updown; // Count up (1) or down (0)
+reg irq_ena; // Enable interrupt on timeout
+reg chain; // Chain to a secondary timer
+
+// Configuration register
+
+assign reg_cfg_do = {27'd0, irq_ena, chain, updown, oneshot, enable};
+
+always @(posedge clkin or negedge resetn) begin
+ if (resetn == 1'b0) begin
+ enable <= 1'b0;
+ oneshot <= 1'b0;
+ updown <= 1'b0;
+ chain <= 1'b0;
+ irq_ena <= 1'b0;
+ end else begin
+ if (reg_cfg_we) begin
+ enable <= reg_cfg_di[0];
+ oneshot <= reg_cfg_di[1];
+ updown <= reg_cfg_di[2];
+ chain <= reg_cfg_di[3];
+ irq_ena <= reg_cfg_di[4];
+ end
+ end
+end
+
+// Counter/timer reset value register
+
+assign reg_val_do = value_reset;
+
+always @(posedge clkin or negedge resetn) begin
+ if (resetn == 1'b0) begin
+ value_reset <= 32'd0;
+ end else begin
+ if (reg_val_we[3]) value_reset[31:24] <= reg_val_di[31:24];
+ if (reg_val_we[2]) value_reset[23:16] <= reg_val_di[23:16];
+ if (reg_val_we[1]) value_reset[15:8] <= reg_val_di[15:8];
+ if (reg_val_we[0]) value_reset[7:0] <= reg_val_di[7:0];
+ end
+end
+
+assign reg_dat_do = value_cur;
+
+// Counter/timer current value register and timer implementation
+
+assign value_cur_plus = value_cur + 1;
+assign value_cur_minus = value_cur - 1;
+
+assign loc_enable = enable_in && enable;
+assign loc_enable = (chain == 1'b1) ? (enable && enable_in) : enable;
+assign enable_out = enable;
+
+// If counting up and the stop condition on the low 32 bits is zero,
+// then signal to the high word counter that the stop condition of the
+// high word must be adjusted by one, since it will roll over at the same
+// time and must be signaled early.
+
+assign is_offset = ((updown == 1'b1) && (value_reset == 0));
+
+// When acting as low 32-bit word of a 64-bit chained counter:
+// It sets the output strobe on the stop condition, one cycle early.
+// It stops on the stop condition if "stop_in" is high.
+
+always @(posedge clkin or negedge resetn) begin
+ if (resetn == 1'b0) begin
+ value_cur <= 32'd0;
+ strobe <= 1'b0;
+ stop_out <= 1'b0;
+ irq_out <= 1'b0;
+ lastenable <= 1'b0;
+ end else begin
+ lastenable <= loc_enable;
+
+ if (reg_dat_we != 4'b0000) begin
+ if (reg_dat_we[3] == 1'b1) value_cur[31:24] <= reg_dat_di[31:24];
+ if (reg_dat_we[2] == 1'b1) value_cur[23:16] <= reg_dat_di[23:16];
+ if (reg_dat_we[1] == 1'b1) value_cur[15:8] <= reg_dat_di[15:8];
+ if (reg_dat_we[0] == 1'b1) value_cur[7:0] <= reg_dat_di[7:0];
+
+ end else if (loc_enable == 1'b1) begin
+ /* IRQ signals one cycle after stop_out, if IRQ is enabled */
+ irq_out <= (irq_ena) ? stop_out : 1'b0;
+
+ if (updown == 1'b1) begin
+ if (lastenable == 1'b0) begin
+ value_cur <= 32'd0;
+ strobe <= 1'b0;
+ stop_out <= 1'b0;
+ end else if (chain == 1'b1) begin
+ // Rollover strobe (2 clock cycles advanced)
+ if (value_cur == -1) begin
+ strobe <= 1'b1;
+ end else begin
+ strobe <= 1'b0;
+ end
+
+ // Chained counter behavior
+ if ((stop_in == 1'b1) && (value_cur == value_reset)) begin
+ if (oneshot != 1'b1) begin
+ value_cur <= 32'd0;
+ stop_out <= 1'b0;
+ end else begin
+ stop_out <= 1'b1;
+ end
+ end else begin
+ if ((stop_in == 1'b1) && (value_cur_plus == value_reset)) begin
+ stop_out <= 1'b1;
+ end else begin
+ stop_out <= 1'b0;
+ end
+ value_cur <= value_cur_plus; // count up
+ end
+ end else begin
+
+ // Single 32-bit counter behavior
+ if (value_cur == value_reset) begin
+ if (oneshot != 1'b1) begin
+ value_cur <= 32'd0;
+ stop_out <= 1'b0;
+ end else begin
+ stop_out <= 1'b1;
+ end
+ end else begin
+ if (value_cur_plus == value_reset) begin
+ stop_out <= 1'b1;
+ end else begin
+ stop_out <= 1'b0;
+ end
+ value_cur <= value_cur_plus; // count up
+ end
+ end
+ end else begin
+ if (lastenable == 1'b0) begin
+ value_cur <= value_reset;
+ stop_out <= 1'b0;
+ strobe <= 1'b0;
+ end else if (chain == 1'b1) begin
+ // Rollover strobe (2 clock cycles advanced)
+ if (value_cur == 2) begin
+ strobe <= 1'b1;
+ end else begin
+ strobe <= 1'b0;
+ end
+
+ // Chained counter behavior
+ if ((stop_in == 1'b1) && (value_cur == 32'd0)) begin
+ if (oneshot != 1'b1) begin
+ value_cur <= value_reset;
+ stop_out <= 1'b0;
+ end else begin
+ stop_out <= 1'b1;
+ end
+ end else begin
+ if ((stop_in == 1'b1) && (value_cur_minus == 32'd0)) begin
+ stop_out <= 1'b1;
+ end else begin
+ stop_out <= 1'b0;
+ end
+ value_cur <= value_cur_minus; // count down
+ end
+ end else begin
+
+ // Single 32-bit counter behavior
+ if (value_cur == 32'd0) begin
+ if (oneshot != 1'b1) begin
+ value_cur <= value_reset;
+ stop_out <= 1'b0;
+ end else begin
+ stop_out <= 1'b1;
+ end
+ end else begin
+ if (value_cur_minus == 32'd0) begin
+ stop_out <= 1'b1;
+ end else begin
+ stop_out <= 1'b0;
+ end
+ value_cur <= value_cur_minus; // count down
+ end
+ end
+ end
+ end else begin
+ strobe <= 1'b0;
+ end
+ end
+end
+
+endmodule
