Started adding RTL for the Caravel project
diff --git a/verilog/rtl/simpleuart.v b/verilog/rtl/simpleuart.v
new file mode 100644
index 0000000..50808cb
--- /dev/null
+++ b/verilog/rtl/simpleuart.v
@@ -0,0 +1,137 @@
+/*
+ * PicoSoC - A simple example SoC using PicoRV32
+ *
+ * Copyright (C) 2017 Clifford Wolf <clifford@clifford.at>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ *
+ */
+
+module simpleuart (
+ input clk,
+ input resetn,
+
+ output ser_tx,
+ input ser_rx,
+
+ input [3:0] reg_div_we,
+ input [31:0] reg_div_di,
+ output [31:0] reg_div_do,
+
+ input reg_dat_we,
+ input reg_dat_re,
+ input [31:0] reg_dat_di,
+ output [31:0] reg_dat_do,
+ output reg_dat_wait
+);
+ reg [31:0] cfg_divider;
+
+ reg [3:0] recv_state;
+ reg [31:0] recv_divcnt;
+ reg [7:0] recv_pattern;
+ reg [7:0] recv_buf_data;
+ reg recv_buf_valid;
+
+ reg [9:0] send_pattern;
+ reg [3:0] send_bitcnt;
+ reg [31:0] send_divcnt;
+ reg send_dummy;
+
+ assign reg_div_do = cfg_divider;
+
+ assign reg_dat_wait = reg_dat_we && (send_bitcnt || send_dummy);
+ assign reg_dat_do = recv_buf_valid ? recv_buf_data : ~0;
+
+ always @(posedge clk) begin
+ if (!resetn) begin
+ cfg_divider <= 1;
+ end else begin
+ if (reg_div_we[0]) cfg_divider[ 7: 0] <= reg_div_di[ 7: 0];
+ if (reg_div_we[1]) cfg_divider[15: 8] <= reg_div_di[15: 8];
+ if (reg_div_we[2]) cfg_divider[23:16] <= reg_div_di[23:16];
+ if (reg_div_we[3]) cfg_divider[31:24] <= reg_div_di[31:24];
+ end
+ end
+
+ always @(posedge clk) begin
+ if (!resetn) begin
+ recv_state <= 0;
+ recv_divcnt <= 0;
+ recv_pattern <= 0;
+ recv_buf_data <= 0;
+ recv_buf_valid <= 0;
+ end else begin
+ recv_divcnt <= recv_divcnt + 1;
+ if (reg_dat_re)
+ recv_buf_valid <= 0;
+ case (recv_state)
+ 0: begin
+ if (!ser_rx)
+ recv_state <= 1;
+ recv_divcnt <= 0;
+ end
+ 1: begin
+ if (2*recv_divcnt > cfg_divider) begin
+ recv_state <= 2;
+ recv_divcnt <= 0;
+ end
+ end
+ 10: begin
+ if (recv_divcnt > cfg_divider) begin
+ recv_buf_data <= recv_pattern;
+ recv_buf_valid <= 1;
+ recv_state <= 0;
+ end
+ end
+ default: begin
+ if (recv_divcnt > cfg_divider) begin
+ recv_pattern <= {ser_rx, recv_pattern[7:1]};
+ recv_state <= recv_state + 1;
+ recv_divcnt <= 0;
+ end
+ end
+ endcase
+ end
+ end
+
+ assign ser_tx = send_pattern[0];
+
+ always @(posedge clk) begin
+ if (reg_div_we)
+ send_dummy <= 1;
+ send_divcnt <= send_divcnt + 1;
+ if (!resetn) begin
+ send_pattern <= ~0;
+ send_bitcnt <= 0;
+ send_divcnt <= 0;
+ send_dummy <= 1;
+ end else begin
+ if (send_dummy && !send_bitcnt) begin
+ send_pattern <= ~0;
+ send_bitcnt <= 15;
+ send_divcnt <= 0;
+ send_dummy <= 0;
+ end else
+ if (reg_dat_we && !send_bitcnt) begin
+ send_pattern <= {1'b1, reg_dat_di[7:0], 1'b0};
+ send_bitcnt <= 10;
+ send_divcnt <= 0;
+ end else
+ if (send_divcnt > cfg_divider && send_bitcnt) begin
+ send_pattern <= {1'b1, send_pattern[9:1]};
+ send_bitcnt <= send_bitcnt - 1;
+ send_divcnt <= 0;
+ end
+ end
+ end
+endmodule
