Cut 1 at an onboard bootloader

[fpgaboy.git] / Uart.v

diff --git a/Uart.v b/Uart.v
index e5213044f684b88f1812e011800883bebcf2bd69..332620bde94fa765a5cbdb4cd376d1bc0ff80f41 100644 (file)
--- a/Uart.v
+++ b/Uart.v
@@ -10,7 +10,8 @@ module UART(
        input rd,
        input [15:0] addr,
        inout [7:0] data,
-       output reg serial = 1);
+       output reg serial = 1,
+       input serialrx);
 
        wire data_decode = (addr == `DATA_ADDR);
        wire stat_decode = (addr == `STAT_ADDR);
@@ -19,22 +20,27 @@ module UART(
        
        reg [7:0] tx_data = 0;
        reg [15:0] tx_clkdiv = 0;
-       reg [3:0] tx_state = 4'b1011;   // 1011 is the not busy state.
-       wire tx_busy = tx_state != 4'b1011;
+       reg [3:0] tx_state = 4'b0000;
+       reg tx_busy = 0;
        wire tx_newdata = (wr) && (!tx_busy) && data_decode;
        
-       assign data = (rd && stat_latch) ? (tx_busy ? 8'b1 : 8'b0) :
-                       (rd && data_latch) ? (8'b0) :
+       reg rx_hasdata = 0;
+       reg [15:0] rx_clkdiv = 0;
+       reg [3:0] rx_state = 4'b0000;
+       reg [7:0] rx_data;
+       
+       assign data = (stat_latch) ? {6'b0, rx_hasdata, tx_busy} :
+                       (data_latch) ? rx_data :
                        8'bzzzzzzzz;
 
        always @(posedge clk)
        begin
                data_latch <= rd && data_decode;
                stat_latch <= rd && stat_decode;
-               /* deal with diqing */
                if(tx_newdata) begin
                        tx_data <= data;
                        tx_state <= 4'b0000;
+                       tx_busy <= 1;
                end else if (tx_clkdiv == 0) begin
                        tx_state <= tx_state + 1;
                        if (tx_busy)
@@ -49,14 +55,44 @@ module UART(
                                4'b0111: serial <= tx_data[6];
                                4'b1000: serial <= tx_data[7];
                                4'b1001: serial <= 1;
-                               4'b1010: serial <= 1;
+                               4'b1010: tx_busy <= 0;
                                default: $stop;
+                               endcase
+               end
+               
+               if ((rx_state == 0) && (serialrx == 0) /*&& (rx_hasdata == 0)*/)                /* Kick off. */
+                       rx_state <= 4'b0001;
+               else if ((rx_state != 4'b0000) && (rx_clkdiv == 0)) begin
+                       if (rx_state != 4'b1010)
+                               rx_state <= rx_state + 1;
+                       else
+                               rx_state <= 0;
+                       case (rx_state)
+                       4'b0001:        begin end /* Twiddle thumbs -- this is the end of the half bit. */
+                       4'b0010:        rx_data[0] <= serialrx;
+                       4'b0011:        rx_data[1] <= serialrx;
+                       4'b0100:        rx_data[2] <= serialrx;
+                       4'b0101:        rx_data[3] <= serialrx;
+                       4'b0110:        rx_data[4] <= serialrx;
+                       4'b0111:        rx_data[5] <= serialrx;
+                       4'b1000:        rx_data[6] <= serialrx;
+                       4'b1001:        rx_data[7] <= serialrx;
+                       4'b1010:        begin end /* Expect a 1 */
                        endcase
                end
+               
+               rx_hasdata <= (rx_hasdata && ~(rd && data_decode)) || ((rx_state == 4'b1010) && (tx_clkdiv == 0));
 
-               if((tx_newdata && !tx_busy) || (tx_clkdiv == `CLK_DIV))
+               if(tx_newdata || (tx_clkdiv == `CLK_DIV))
                        tx_clkdiv <= 0;
                else
                        tx_clkdiv <= tx_clkdiv + 1;
+               
+               if ((rx_state == 0) && (serialrx == 0) /*&& (rx_hasdata == 0)*/)                /* Wait half a period before advancing. */
+                       rx_clkdiv <= `CLK_DIV / 2 + `CLK_DIV / 4;
+               else if (rx_clkdiv == `CLK_DIV)
+                       rx_clkdiv <= 0;
+               else
+                       rx_clkdiv <= rx_clkdiv + 1;
        end
 endmodule