From b9fe1e4bcf9271288c5ad9d605926b2b7044cb3b Mon Sep 17 00:00:00 2001
From: Ryan Holtz <rholtz@batcountryentertainment.com>
Date: Fri, 18 Jan 2008 04:33:13 +0000
Subject: [PATCH] On-the-DL credit: "SGINut"

Changes:
- Re-fixed RSP single-step activation behavior
- Reading the RSP PC returns only the least significant 12 bits
- Fixed flag behavior when read out via CFC2
---
 src/emu/cpu/rsp/rsp.c  | 18 +++++++++++++++---
 src/mame/machine/n64.c |  2 +-
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/src/emu/cpu/rsp/rsp.c b/src/emu/cpu/rsp/rsp.c
index 10239719934..7fa25bd272b 100644
--- a/src/emu/cpu/rsp/rsp.c
+++ b/src/emu/cpu/rsp/rsp.c
@@ -2685,7 +2685,19 @@ static int rsp_execute(int cycles)
 						// ------------------------------------------------
 						//
 
-						if (RTREG) RTVAL = rsp.flag[RDREG];
+                        if (RTREG)
+                        {
+                            if (RDREG == 2)
+                            {
+                                // Anciliary clipping flags
+                                RTVAL = rsp.flag[RDREG] & 0x00ff;
+                            }
+                            else
+                            {
+                                // All other flags are 16 bits but sign-extended at retrieval
+                                RTVAL = (UINT32)rsp.flag[RDREG] | ( ( rsp.flag[RDREG] & 0x8000 ) ? 0xffff0000 : 0 );
+                            }
+                        }
 						break;
 					}
 					case 0x04:	/* MTC2 */
@@ -2890,8 +2902,8 @@ static void rsp_set_info(UINT32 state, cpuinfo *info)
             rsp.sr = info->i;
             if( info->i & RSP_STATUS_SSTEP )
             {
-                // Heaven help me for putting this check here, but it's accurate to the hardware.
-                rsp.step_count = ( cpu_getactivecpu() == 0 ) ? 1 : 0;
+                // Heaven help me for putting this check here, but it's accurate to the hardware and works.
+                rsp.step_count = ( cpu_getactivecpu() == 0 ) ? 0 : 1;
             }
             break;
         case CPUINFO_INT_REGISTER + RSP_NEXTPC:         rsp.nextpc = info->i;        break;
diff --git a/src/mame/machine/n64.c b/src/mame/machine/n64.c
index 8a25201ce9b..e3aa298cc8d 100644
--- a/src/mame/machine/n64.c
+++ b/src/mame/machine/n64.c
@@ -282,7 +282,7 @@ READ32_HANDLER( n64_sp_reg_r )
             return 0;
 
         case 0x40000/4:     // PC
-            return cpunum_get_info_int(1, CPUINFO_INT_REGISTER + RSP_PC);
+            return cpunum_get_info_int(1, CPUINFO_INT_REGISTER + RSP_PC) & 0x00000fff;
 
         default:
             logerror("sp_reg_r: %08X, %08X at %08X\n", offset, mem_mask, activecpu_get_pc());