Add comments.

spi_slave.sv

@@ -1,3 +1,14 @@
+/**
+ * Specialized SPI slave.
+ * Reads width bits at a time, and sets the ready flag
+ * whenever a full 32 bits has been read. Also, recognizes
+ * 0x00 as a pattern, and when full 0s are read, sets the done flag.
+ * 0x00 is a special value in the CPU programming process that indicates
+ * end-of-program.
+ *
+ * master_clk, ss, and mosi are all SPI-specific inputs.
+ * data should only be read when ready is high.
+ */
 module spi_slave #(width=32)
 				  (input logic clk, reset,
 				   input logic master_clk, ss, mosi,
@@ -7,7 +18,7 @@ module spi_slave #(width=32)
 	logic [width-1:0] storage;
 	logic unsigned [$clog2(width)-1:0] counter;
 	logic old_clk;
-	
+
 	always_ff@(posedge clk)
 		if(reset) begin
 			counter <= 0;
@@ -30,7 +41,7 @@ module spi_slave #(width=32)
 			end
 			old_clk <= master_clk;
 		end
-	
+
 	assign data = storage;
-	
-endmodule
+
+endmodule