Squashed B200 FPGA Source. Code from Josh Blum, Ian Buckley, and Matt Ettus.

Original-commit: 0df4b801a34697f2058b4a7b95e08d2a0576c9db

lib/packet_proc/source_flow_control.v

@@ -0,0 +1,127 @@
+
+// source_flow_control.v
+//
+//  This block passes the in_* AXI port to the out_* AXI port only when it has
+//   enough flow control credits.  Data is held when there are not enough credits.
+//  Credits are replenished with extension context packets which update the 
+//   last_consumed packet register.  Max credits are controlled by settings regs.
+//  The 2nd line of the packet contains the sequence number in the low 12 bits.
+//  These packets should not have a time value, but if they do it will be ignored.
+
+module source_flow_control
+  #(parameter BASE=0)
+   (input clk, input reset, input clear,
+    input set_stb, input [7:0] set_addr, input [31:0] set_data,
+    input [63:0] fc_tdata, input fc_tlast, input fc_tvalid, output fc_tready,
+    input [63:0] in_tdata, input in_tlast, input in_tvalid, output in_tready,
+    output [63:0] out_tdata, output out_tlast, output out_tvalid, input out_tready);
+   
+   reg [31:0] 	  last_seqnum_consumed;
+   wire [31:0] 	  window_size;
+   wire [31:0] 	  go_until_seqnum = last_seqnum_consumed + window_size + 1;
+   reg [31:0] 	  current_seqnum;
+   wire 	  window_reset;
+   wire 	  window_enable;
+   wire 	  setting_changed;
+   
+   setting_reg #(.my_addr(BASE)) sr_window_size
+     (.clk(clk),.rst(reset),.strobe(set_stb),.addr(set_addr),.in(set_data),
+      .out(window_size),.changed(setting_changed));
+
+   setting_reg #(.my_addr(BASE+1), .width(1)) sr_window_enable
+     (.clk(clk),.rst(reset),.strobe(set_stb),.addr(set_addr),.in(set_data),
+      .out(window_enable),.changed(window_reset));
+
+   reg 		  go;
+   reg [1:0] 	  sfc_state;
+  
+   
+   localparam SFC_HEAD = 2'd0;
+   localparam SFC_TIME = 2'd1;
+   localparam SFC_BODY = 2'd2;
+   localparam SFC_DUMP = 2'd3;
+
+   always @(posedge clk)
+     if(reset | clear | window_reset)
+       begin
+	  last_seqnum_consumed <= 32'hFFFFFFFF;
+	  sfc_state <= SFC_HEAD;
+       end
+     else
+       if(fc_tvalid & fc_tready)
+	 case(sfc_state)
+	   SFC_HEAD :
+	     if(fc_tlast)
+	       sfc_state <= SFC_HEAD; // Error. CHDR packet with only a header is an error.
+	     else if(~fc_tdata[63])   // Is this NOT an extension context packet?
+	       sfc_state <= SFC_DUMP; // Error. Only extension context packets should come in on this interface.
+	     else if(fc_tdata[61])    // Does this packet have time?
+	       sfc_state <= SFC_TIME;
+	     else
+	       sfc_state <= SFC_BODY;
+	   
+	   SFC_TIME :
+	     if(fc_tlast)
+	       sfc_state <= SFC_HEAD; // Error, CHDR packet with only header and time is an error.
+	     else
+	       sfc_state <= SFC_BODY;
+	   
+	   SFC_BODY :
+	     begin
+		last_seqnum_consumed <= fc_tdata[31:0]; // Sequence number is in lower 32bits.
+		if(fc_tlast)
+		  sfc_state <= SFC_HEAD;
+		else
+		  sfc_state <= SFC_DUMP; // Error. Not expecting any more data in a CHDR packet.
+	     end
+
+	   SFC_DUMP :   // shouldn't ever need to be here, this is an error condition
+	     if(fc_tlast)
+	       sfc_state <= SFC_HEAD;
+	 endcase // case (sfc_state)
+      
+   assign fc_tready = 1'b1;  // Always consume FC -- FIXME Even if we are getting reset?
+   assign out_tdata = in_tdata; // CHDR data flows through combinatorially.
+   assign out_tlast = in_tlast;
+   assign in_tready = go ? out_tready : 1'b0;
+   assign out_tvalid = go ? in_tvalid : 1'b0;
+
+   //
+   // Each time we recieve the end of an IF data packet increment the current_seqnum.
+   // We bravely assume that no packets go missing...or at least that they will be detected elsewhere
+   // and then handled appropriately.
+   // The SEQNUM needs to be initialized every time we start a new stream. In new_rx_framer this is done
+   // as a side effect of writing a new SID value to the setting reg.
+   //
+   // By incrementing current_seqnum on the last signal we get the nice effect that packet flow is 
+   // always suspended between packets rather than within a packet.
+   //
+   always @(posedge clk)
+     if(reset | clear | window_reset)
+       current_seqnum <= 0;
+     else if (in_tvalid && in_tready && in_tlast)
+       current_seqnum <= current_seqnum + 1;
+
+   always @(posedge clk)
+     if(reset | clear)
+       go <= 1'b0;
+     else
+       if(~window_enable)
+	 go <= 1'b1;
+       else 
+	 case(go)
+	   1'b0 :
+	     // This test assumes the host is well behaved in sending good numbers for packets consumed
+	     // and that current_seqnum increments always by 1 only.
+	     // This way wraps are dealt with without a large logic penalty.
+	     if (in_tvalid & (go_until_seqnum - current_seqnum != 0))
+	     // 	     if(in_tvalid & (go_until_seqnum > current_seqnum))  // FIXME will need to handle wrap of 32-bit seqnum
+	       go <= 1'b1;
+	   
+	   1'b1 :
+	     if(in_tvalid & in_tready & in_tlast)
+	       go <= 1'b0;
+	 endcase // case (go)
+
+   
+endmodule // source_flow_control