From afa9bdf8f2749eadf503fdcac6003111a29e02c4 Mon Sep 17 00:00:00 2001
From: harbaum <till@harbaum.org>
Date: Wed, 29 Apr 2015 08:42:34 +0000
Subject: [PATCH] [ATARI ST] Ignore both floppies being selected at same time.
 Fixes Violator A_496.

---
 cores/mist/audio.v    |  2 +-
 cores/mist/fdc.v      | 25 +++++++++++++++----------
 cores/mist/mist_top.v |  3 +--
 3 files changed, 17 insertions(+), 13 deletions(-)

diff --git a/cores/mist/audio.v b/cores/mist/audio.v
index 0490fcf..39f46fb 100644
--- a/cores/mist/audio.v
+++ b/cores/mist/audio.v
@@ -84,7 +84,7 @@ wire [7:0] port_b_in = { ~joy0[0], ~joy0[1], ~joy0[2], ~joy0[3],
 								 ~joy1[0], ~joy1[1], ~joy1[2], ~joy1[3]}; 
 wire [7:0] port_a_in = { 2'b11, ~joy1[4], 5'b11111 }; 
 
-assign dout = psg_sel?{psg_dout,8'h00}:ste_dma_snd_sel?ste_dma_snd_data_out:16'h0000;
+assign dout = psg_sel?{psg_dout,8'hff}:ste_dma_snd_sel?ste_dma_snd_data_out:16'h0000;
 wire [15:0] ste_dma_snd_data_out;
 wire [7:0] psg_dout;
 
diff --git a/cores/mist/fdc.v b/cores/mist/fdc.v
index d45418f..ff1fca7 100644
--- a/cores/mist/fdc.v
+++ b/cores/mist/fdc.v
@@ -25,20 +25,20 @@ module fdc (
 	input 		 reset,
 
 	    // write protection of currently selected floppy
-	input [1:0] 	 drv_sel,
+	input [1:0]  drv_sel,
 	input 		 drv_side,
 	input 		 wr_prot,
 	    
 	input 		 dma_ack,
-	input [2:0] 	 status_sel,
-	output [7:0]     status_byte,
+	input [2:0]  status_sel,
+	output [7:0] status_byte,
 
-	    // cpu interface
-        input [1:0] 	 cpu_addr,
-        input 		 cpu_sel,
-        input 		 cpu_rw,
-        input [7:0] 	 cpu_din,
-        output [7:0] cpu_dout,
+	// cpu interface
+   input [1:0]  cpu_addr,
+   input 		 cpu_sel,
+   input 		 cpu_rw,
+   input [7:0]  cpu_din,
+   output [7:0] cpu_dout,
 
 	output reg 	 irq		 
 );
@@ -58,13 +58,18 @@ reg [7:0] track;
 reg [7:0] sector;
 reg [7:0] data;
 
+// Some broken software selects both drives at the same time. On real hardware this
+// only works if no second drive is present. In our setup the second drive is present
+// but we can simply map all such broken accesses to drive A only
+wire [1:0] drv_sel_exclusive = (drv_sel == 2'b00)?2'b10:drv_sel;
+
 // fdc status as reported to the io controller
 assign status_byte =
     (status_sel == 0)?cmd:
     (status_sel == 1)?track:
     (status_sel == 2)?sector:
     (status_sel == 3)?8'h00: // data:
-    (status_sel == 4)?{ 4'b0000, drv_sel, drv_side, state == STATE_IO_WAIT }:
+    (status_sel == 4)?{ 4'b0000, drv_sel_exclusive, drv_side, state == STATE_IO_WAIT }:
     8'h00;
 
 reg step_dir;
diff --git a/cores/mist/mist_top.v b/cores/mist/mist_top.v
index 695fc69..db39a18 100644
--- a/cores/mist/mist_top.v
+++ b/cores/mist/mist_top.v
@@ -234,11 +234,10 @@ wire [15:0] dma_data_out;
 // --------- de-multiplex the various io data output ports into one -----------
 // acia returns 0xff on odd addresses (needed e.g. by intro of automation 496)
 wire [15:0] acia_data_out_16 = { acia_data_out, acia_sel?8'hff:8'h00 };
-wire io_data_out_8l_sel = mmu_sel | mfp_sel | auto_iack | mste_ctrl_sel;
 wire [15:0] mfp_data_out_16 = { mfp_sel?8'hff:8'h00, mfp_data_out };
 wire [15:0] mmu_data_out_16 = { mmu_sel?8'hff:8'h00, mmu_data_out };
 wire [15:0] mste_ctrl_data_out_16 = { mste_ctrl_sel?8'hff:8'h00, mste_ctrl_data_out };
-// wire [7:0] io_data_out_8l = mste_ctrl_data_out;
+
 wire [15:0] io_data_out = vreg_data_out | dma_data_out | blitter_data_out | 
 				ste_joy_data_out | audio_data_out | rom_data_out | { 8'h00, auto_vector } |
 				mfp_data_out_16 | mmu_data_out_16 | mste_ctrl_data_out_16 | acia_data_out_16;