Use 7-seg LED to simulate the sound generator

3 files changed, 47 insertions, 17 deletions

diff --git a/CHANGES b/CHANGES
new file mode 100644
index 0000000..ae2adb5
--- /dev/null
+++ b/CHANGES
@@ -0,0 +1,7 @@
+Changes in release 3:
+---------------------
+
+* 80-column mode now properly supported, including switching the BASIC
+  ROM.
+
+* The 7-segment LED is used as a substitute for the sound generator.
diff --git a/README b/README
index 8a78ff6..0560daf 100644
--- a/README
+++ b/README
@@ -35,8 +35,9 @@ To read the current memory maps:
 
    in maps,(132)
 
-=> Eventually this will also support the out (7),map used by
-   Mikrodatorn's 64K expansion.
+The MMU also supports "out (7),map" for compatibility with
+Mikrodatorn's 64K expansion.  This sets all the maps to the same
+value.
 
 The top 4 bits of the physical page indicate memory device; the rest
 is address; see data/mmuinit.pl for which memory devices exist.
diff --git a/abc80.v b/abc80.v
index adb6cd4..b9c2b6a 100644
--- a/abc80.v
+++ b/abc80.v
@@ -233,6 +233,10 @@ module abc80 (
    // for I/O devices to snoop the bus.
    wire 	 cpu_reti_n;	// RETI# from CPU
    
+   // ABC-bus decoded strobes
+   reg [7:0] 	 abc_out_n;
+   reg [7:0] 	 abc_in_n;
+   
    // ------------------------------------------------------------------------
    //  Keyboard controller
    // ------------------------------------------------------------------------
@@ -542,6 +546,11 @@ module abc80 (
 		      mmu_map_sel <= cpu_do[5:0];
 		  endcase // case( cpu_a[2:0] )
 	       end // if ( mmu_sel & ~cpu_wr_n )
+	     else if ( ~abc_out_n[7] )
+	       begin
+		  // For compatibility with Mikrodatorn's 64K hack
+		  mmu_map_sel <= { cpu_do[1:0], cpu_do[1:0], cpu_do[1:0] };
+	       end
 	     else if ( mmu_sel & ~cpu_rd_n )
 	       begin
 		  case ( cpu_a[2:0] )
@@ -631,9 +640,7 @@ module abc80 (
    // ------------------------------------------------------------------------
    //  ABC-bus
    // ------------------------------------------------------------------------
-
-   reg [7:0]  abc_out_n;
-   reg [7:0]  abc_in_n;
+   
    wire       abc_sel;
    
    always @(*)
@@ -671,7 +678,7 @@ module abc80 (
    wire [7:0] abc_cf_di;
    wire       cf_select;
    wire [8:0] cf_debug;
-   
+
    cfcontroller cfcontroller (
 			      .reset_n ( reset_n ),
 			      .clk ( cpu_clk ),
@@ -700,7 +707,12 @@ module abc80 (
 			      .debug ( cf_debug )
 			      );
 
-   assign     led[0] = cf_select; // Closest thing we get to a disk LED
+   // The terminology gets a bit funny there.  abc_do means data from
+   // the ABC-bus to the main CPU.
+   wire [7:0] abc_do = abc_cf_di;
+
+   // Closest thing we get to a disk LED
+   assign     led[0] = cf_select;
 
    // Video width control INP 4 = 80, INP 3 = 40
    always @(negedge reset_n or posedge cpu_clk)
@@ -713,23 +725,33 @@ module abc80 (
 	  else if ( ~abc_in_n[4] )
 	    video_width <= 1;
      end
-      
-   // The terminology gets a bit funny there.  abc_do means data from
-   // the ABC-bus to the main CPU.
-   wire [7:0] abc_do = abc_cf_di;
 
-   // Debugging...
-   hexled hexled0 (
-		    .value( cf_debug[3:0] ),
+   // Sound generator (not actually implemented, but flash the 7seg LEDs
+   reg [7:0] sound;
+   always @(negedge reset_n or posedge cpu_clk)
+     begin
+	if ( ~reset_n )
+	  sound <= 0;
+	else
+	  if ( ~abc_out_n[6] )
+	    sound <= cpu_do;
+     end
+      
+   hexledx hexled0 (
+		    .value( sound[3:0] ),
+		    .blank( ~sound[0] ),
+		    .minus( 0 ),
 		    .s7 ( s7_0[6:0] )
 		   );
-   hexled hexled1 (
-		    .value( cf_debug[7:4] ),
+   hexledx hexled1 (
+		    .value( sound[7:4] ),
+		    .blank( ~sound[0] ),
+		    .minus( 0 ),
 		    .s7 ( s7_1[6:0] )
 		   );
 
    assign s7_0[7] = 1'b1;
-   assign s7_1[7] = ~cf_debug[8];
+   assign s7_1[7] = 1'b1;
    
    // ------------------------------------------------------------------------
    //  I/O address decoding