fix pit_busy_wait; better tasking

kernel.cpp

@@ -10,6 +10,8 @@
 static VGATerminal vga;
 TextOutput& term = vga;
 
+static volatile bool termBusy = false;
+
 void kernel_main(void) 
 {
     term.write("Clyne's kernel, v2024\n\n");
@@ -28,18 +30,41 @@ void kernel_main(void)
     gdt_initialize();
     pic_initialize();
     idt_initialize();
-    pit_initialize(50);
+    pit_initialize(100);
     asm volatile("sti");
     tasking_initialize();
     term.write("Tasking enabled.\n");
 
     tasking_spawn([] {
-        for (;;)
+        for (;;) {
+            do pit_busy_wait(1);
+            while (termBusy);
+
+            termBusy = true;
             term.write('B');
+            termBusy = false;
+        }
+    }, 256);
+
+    tasking_spawn([] {
+        for (;;) {
+            do pit_busy_wait(1);
+            while (termBusy);
+
+            termBusy = true;
+            term.write('C');
+            termBusy = false;
+        }
     }, 256);
 
-    for (;;)
+    for (;;) {
+        do pit_busy_wait(1);
+        while (termBusy);
+
+        termBusy = true;
         term.write('A');
+        termBusy = false;
+    }
 }
 
 extern "C"

pit.cpp

@@ -33,7 +33,7 @@ void pit_initialize(std::uint32_t frequency)
 void pit_busy_wait(std::int32_t tks)
 {
     const auto end = ticks + tks;
-    while (end - ticks > 0)
+    while (static_cast<std::int32_t>(end - ticks) > 0)
         asm volatile("nop");
 }
 

tasking.cpp

@@ -7,6 +7,7 @@ struct Task
     enum class State {
         Invalid,
         Staging,
+        Staged,
         Running
     };
 
@@ -33,14 +34,14 @@ void schedule(const Registers& regs)
     do {
         if (++current >= tasks.size())
             current = 0;
-    } while (tasks[current].state == Task::Invalid);
+    } while (tasks[current].state == Task::Invalid || tasks[current].state == Task::Staging);
 
     asm volatile(R"(
         mov %0, %%esp
         mov %1, %%ebp
     )" :: "m" (tasks[current].esp), "m" (tasks[current].ebp));
 
-    if (tasks[current].state == Task::Staging) {
+    if (tasks[current].state == Task::Staged) {
         tasks[current].state = Task::Running;
         asm volatile(R"(
             pop %eax
@@ -69,7 +70,7 @@ bool tasking_spawn(void (*entry)(), unsigned ssize)
     if (i < 0)
         return false;
 
-    tasks[i] = Task();
+    tasks[i].state = Task::Staging;
 
     auto stack = reinterpret_cast<std::uint32_t>(new std::uint8_t[ssize]);
     const auto stackend = stack + ssize;
@@ -81,9 +82,11 @@ bool tasking_spawn(void (*entry)(), unsigned ssize)
     r->cs = 0x8;
     asm volatile("pushfl; pop %%eax" : "=a"(r->eflags));
 
-    tasks[i].esp = regbase;
+    tasks[i] = Task {
-    tasks[i].ebp = stackend;
+        .esp = regbase,
-    tasks[i].state = Task::Staging;
+        .ebp = stackend,
+        .state = Task::Staged
+    };
     return true;
 }
 

vgaterminal.cpp

@@ -46,9 +46,11 @@ void VGATerminal::checkpos() noexcept
 
 void VGATerminal::updatecursor() const noexcept
 {
+    asm volatile("cli");
     outb(0x03d4, 0x0f);
     outb(0x03d5, static_cast<std::uint8_t>(offset));
     outb(0x03d4, 0x0e);
     outb(0x03d5, static_cast<std::uint8_t>(offset >> 8));
+    asm volatile("sti");
 }