STOP undocumented special case.

diff --git a/gencpu.cpp b/gencpu.cpp
index 68cc49ee5140d7bedb725c6d4952e5ebd1f2c742..4d869e218a6c3ec886e68fcf5c8808c70c8bf328 100644 (file)
--- a/gencpu.cpp
+++ b/gencpu.cpp
@@ -3809,27 +3809,44 @@ static void gen_opcode (unsigned int opcode)
                fill_prefetch_next ();
                break;
        case i_STOP:
+               next_level_000();
                if (using_prefetch) {
-                       printf ("\tregs.sr = regs.irc;\n");
+                       printf("\tuae_u16 sr = regs.irc;\n");
                        m68k_pc_offset += 2;
                } else {
                        genamode (curi, curi->smode, "srcreg", curi->size, "src", 1, 0, 0);
-                       printf ("\tregs.sr = src;\n");
-               }
-               addcycles000(2 * 4);
+                       printf("\tuae_u16 sr = src;\n");
+               }
+               // STOP undocumented features:
+               // if SR is not set:
+               // 68000 (68010?): Update SR, increase PC and then cause privilege violation exception (handled in newcpu)
+               // 68000 (68010?): Traced STOP also runs 4 cycles faster.
+               // 68020 68030: STOP works normally
+               // 68040 68060: Immediate privilege violation exception
+               if ((cpu_level == 0 || cpu_level == 1) && using_ce) {
+                       printf("\t%s(regs.t1 ? 4 : 8);\n", do_cycles);
+               }
+               if (cpu_level >= 4) {
+                       printf("\tif (!(sr & 0x2000)) {\n");
+                       incpc("%d", m68k_pc_offset);
+                       printf("\t\tException(8); goto %s;\n", endlabelstr);
+                       printf("\t}\n");
+               }
+               printf("\tregs.sr = sr;\n");
                makefromsr();
                printf ("\tm68k_setstopped ();\n");
                sync_m68k_pc ();
                // STOP does not prefetch anything
                did_prefetch = -1;
+               next_cpu_level = cpu_level - 1;
                break;
        case i_LPSTOP: /* 68060 */
                printf ("\tuae_u16 sw = %s (2);\n", srcwi);
-               printf ("\tuae_u16 sr;\n");
                printf ("\tif (sw != (0x100|0x80|0x40)) { Exception (4); goto %s; }\n", endlabelstr);
-               printf ("\tsr = %s (4);\n", srcwi);
-               printf ("\tif (!(sr & 0x8000)) { Exception (8); goto %s; }\n", endlabelstr);
-               printf ("\tregs.sr = sr;\n");
+               printf("\tif (!(regs.sr & 0x2000)) {\n");
+               printf("\t\tException(8); goto %s;\n", endlabelstr);
+               printf("\t}\n");
+               printf("\tregs.sr = %s (4);\n", srcwi);
                makefromsr();
                printf ("\tm68k_setstopped();\n");
                m68k_pc_offset += 4;

diff --git a/newcpu.cpp b/newcpu.cpp
index ad4bb5f584218a42a5e28ca17fbd0c8d52f88282..f92264fd8a685f24327b574ac477a881186bbbda 100644 (file)
--- a/newcpu.cpp
+++ b/newcpu.cpp
@@ -4661,6 +4661,16 @@ static int do_specialties (int cycles)
                unset_special (SPCFLAG_TRAP);
                Exception (3);
        }
+
+       if ((regs.spcflags & SPCFLAG_STOP) && regs.s == 0 && currprefs.cpu_model <= 68010) {
+               // 68000/68010 undocumented special case:
+               // if STOP clears S-bit and T was not set:
+               // cause privilege violation exception, PC pointing to following instruction.
+               // If T was set before STOP: STOP works as documented.
+               m68k_unset_stop();
+               Exception(8);
+       }
+
        bool first = true;
        while ((regs.spcflags & SPCFLAG_STOP) && !(regs.spcflags & SPCFLAG_BRK)) {
        isstopped: