target-mips: fix offset calculation for Interrupts

Correct computation of vector offsets for EXCP_EXT_INTERRUPT.
For instance, if Cause.IV is 0 the vector offset should be 0x180.

Simplify the finding vector number logic for the Vectored Interrupts.
Signed-off-by: NYongbok Kim <yongbok.kim@imgtec.com>
Reviewed-by: NLeon Alrae <leon.alrae@imgtec.com>
[leon.alrae@imgtec.com: cosmetic changes]
Signed-off-by: NLeon Alrae <leon.alrae@imgtec.com>

target-mips/helper.c

@@ -565,34 +565,30 @@ void mips_cpu_do_interrupt(CPUState *cs)
         break;
     case EXCP_EXT_INTERRUPT:
         cause = 0;
-        if (env->CP0_Cause & (1 << CP0Ca_IV))
-            offset = 0x200;
-
-        if (env->CP0_Config3 & ((1 << CP0C3_VInt) | (1 << CP0C3_VEIC))) {
-            /* Vectored Interrupts.  */
-            unsigned int spacing;
-            unsigned int vector;
-            unsigned int pending = (env->CP0_Cause & CP0Ca_IP_mask) >> 8;
-
-            pending &= env->CP0_Status >> 8;
-            /* Compute the Vector Spacing.  */
-            spacing = (env->CP0_IntCtl >> CP0IntCtl_VS) & ((1 << 6) - 1);
-            spacing <<= 5;
-
-            if (env->CP0_Config3 & (1 << CP0C3_VInt)) {
-                /* For VInt mode, the MIPS computes the vector internally.  */
-                for (vector = 7; vector > 0; vector--) {
-                    if (pending & (1 << vector)) {
-                        /* Found it.  */
-                        break;
+        if (env->CP0_Cause & (1 << CP0Ca_IV)) {
+            uint32_t spacing = (env->CP0_IntCtl >> CP0IntCtl_VS) & 0x1f;
+
+            if ((env->CP0_Status & (1 << CP0St_BEV)) || spacing == 0) {
+                offset = 0x200;
+            } else {
+                uint32_t vector = 0;
+                uint32_t pending = (env->CP0_Cause & CP0Ca_IP_mask) >> CP0Ca_IP;
+
+                if (env->CP0_Config3 & (1 << CP0C3_VEIC)) {
+                    /* For VEIC mode, the external interrupt controller feeds
+                     * the vector through the CP0Cause IP lines.  */
+                    vector = pending;
+                } else {
+                    /* Vectored Interrupts
+                     * Mask with Status.IM7-IM0 to get enabled interrupts. */
+                    pending &= (env->CP0_Status >> CP0St_IM) & 0xff;
+                    /* Find the highest-priority interrupt. */
+                    while (pending >>= 1) {
+                        vector++;
                     }
                 }
-            } else {
-                /* For VEIC mode, the external interrupt controller feeds the
-                   vector through the CP0Cause IP lines.  */
-                vector = pending;
+                offset = 0x200 + (vector * (spacing << 5));
             }
-            offset = 0x200 + vector * spacing;
         }
         goto set_EPC;
     case EXCP_LTLBL:

target-mips/op_helper.c

@@ -1432,7 +1432,6 @@ void helper_mttc0_status(CPUMIPSState *env, target_ulong arg1)
 
 void helper_mtc0_intctl(CPUMIPSState *env, target_ulong arg1)
 {
-    /* vectored interrupts not implemented, no performance counters. */
     env->CP0_IntCtl = (env->CP0_IntCtl & ~0x000003e0) | (arg1 & 0x000003e0);
 }
 
@@ -1473,7 +1472,6 @@ target_ulong helper_mftc0_ebase(CPUMIPSState *env)
 
 void helper_mtc0_ebase(CPUMIPSState *env, target_ulong arg1)
 {
-    /* vectored interrupts not implemented */
     env->CP0_EBase = (env->CP0_EBase & ~0x3FFFF000) | (arg1 & 0x3FFFF000);
 }