kernel scheduling now working better with ecalls, not resetting the time slice

kinclude/csr.c

@@ -31,15 +31,3 @@ void write_mtimecmp(unsigned long long int mtimecmp) {
 }
 
 #endif
-
-
-unsigned long long int read_time() {
-    unsigned int lower, higher;
-    __asm__(
-        "csrr %0, %2\n"
-        "csrr %1, %3\n"
-        : "=r"(lower), "=r"(higher)
-        : "i"(CSR_TIME), "i"(CSR_TIMEH)
-    );
-    return (unsigned long long) higher << 32 | lower;
-}

kinclude/csr.h

@@ -36,7 +36,17 @@
 }
 
 void write_mtimecmp(unsigned long long int mtimecmp);
-unsigned long long int read_time();
+
+inline __attribute__((always_inline)) unsigned long long int read_time() {
+    unsigned int lower, higher;
+    __asm__(
+        "csrr %0, %2\n"
+        "csrr %1, %3\n"
+        : "=r"(lower), "=r"(higher)
+        : "i"(CSR_TIME), "i"(CSR_TIMEH)
+    );
+    return (unsigned long long) higher << 32 | lower;
+}
 
 #endif
 

kinclude/ecall.c

@@ -48,6 +48,10 @@ int ecall_handle_exit(int* args, ProcessControlBlock* pcb)
 }
 
 void trap_handle_ecall() {
+    {
+        
+        mark_ecall_entry();
+    };
     ProcessControlBlock* pcb = get_current_process();
     int *regs = pcb->regs;
     int code = regs[16];
@@ -73,19 +77,39 @@ void trap_handle(int interrupt_bit, int code, int mtval)
 {
     if (interrupt_bit) {
         switch (code) {
+            // timer interrupts
+            case 4:
+            case 5:
+            case 6:
             case 7:
               scheduler_run_next();
               break;
             default:
               // impossible
-              HALT(12)
+              HALT(12);
               break;
         }
     } else {
         switch (code) {
-            case 8:    // user ecall
+            // any known exception code:
+            case 0:
+            case 1:
+            case 2:
+            case 4:
+            case 5:
+            case 6:
+            case 7:
+            case 12:
+            case 13:
+            case 15:
+                handle_exception(code, mtval);
+                break;
+            // user or supervisor ecall
+            case 8:    
+            case 9:
                 trap_handle_ecall();
                 break;
+            // unknown code
             default:
                 HALT(13);
         }
@@ -101,4 +125,9 @@ void init_ecall_table()
     ecall_table[ECALL_JOIN]  = ecall_handle_join;
     ecall_table[ECALL_KILL]  = ecall_handle_kill;
     ecall_table[ECALL_EXIT]  = ecall_handle_exit;
-}
+}
+
+void handle_exception(int ecode, int mtval) 
+{
+
+}

kinclude/ecall.h

@@ -33,6 +33,7 @@ int ecall_handle_join(int*, ProcessControlBlock*);
 int ecall_handle_kill(int*, ProcessControlBlock*);
 int ecall_handle_exit(int*, ProcessControlBlock*);
 
+void handle_exception(int ecode, int mtval);
 
 void __attribute__((__noreturn__)) trap_handle(int interrupt_bit, int code, int mtval);
 

kinclude/sched.c

@@ -6,13 +6,14 @@
 // scheduling data:
 ProcessControlBlock processes[PROCESS_COUNT];
 int current_process_index = 1;
+unsigned long long int scheduling_interrupted_start;
+unsigned long long int next_interrupt_scheduled_for;
 
 void scheduler_run_next ()  
 {
     current_process_index = scheduler_select_free();
     // set up timer interrupt
-    unsigned long long int mtimecmp = read_time() + TIME_SLICE_LEN;
+    set_next_interrupt();
-    write_mtimecmp(mtimecmp);
     scheduler_switch_to(current_process_index);
 }
 
@@ -22,9 +23,9 @@ void scheduler_try_return_to(ProcessControlBlock* pcb)
         scheduler_run_next();
     } else {
         current_process_index = scheduler_index_from_pid(pcb->pid);
-        //FIXME: this refreshes the processes time slice which we actually don't want!
+        // add time spent in ecall handler to the processes time slice
-        unsigned long long int mtimecmp = read_time() + TIME_SLICE_LEN;
+        next_interrupt_scheduled_for = next_interrupt_scheduled_for + (read_time() - scheduling_interrupted_start);
-        write_mtimecmp(mtimecmp);
+        write_mtimecmp(next_interrupt_scheduled_for);
         scheduler_switch_to(current_process_index);
     }
 }
@@ -135,3 +136,14 @@ ProcessControlBlock* get_current_process()
 {
     return &processes[current_process_index];
 }
+
+void set_next_interrupt()
+{
+    next_interrupt_scheduled_for = read_time() + TIME_SLICE_LEN;
+    write_mtimecmp(next_interrupt_scheduled_for);
+}
+
+void mark_ecall_entry()
+{
+    scheduling_interrupted_start = read_time();
+}

kinclude/sched.h

@@ -29,11 +29,12 @@ extern ProcessControlBlock processes[PROCESS_COUNT];
 // scheduler methods
 int  scheduler_select_free();
 int  scheduler_create_process(int binid);
+void set_next_interrupt();
 void __attribute__((noreturn)) scheduler_run_next();
 void __attribute__((noreturn)) scheduler_try_return_to(ProcessControlBlock*);
 void __attribute__((noreturn)) scheduler_switch_to(int proc_index);
 int  scheduler_index_from_pid(int pid);
 int* get_current_process_registers();
 ProcessControlBlock* get_current_process();
-
+void mark_ecall_entry();
 #endif