mbv: now with functioning timer interrupts!

And a few other nice things.
The bootloader now has an embedded wozmon!
If you know its offset, you can jump to it from the app.

mbv/hal/intc.cc

@@ -0,0 +1,62 @@
+#include "intc.h"
+
+#include "pol0.h"
+
+namespace {
+
+struct IntC {
+    volatile uint32_t ISR;
+    volatile uint32_t IPR;
+    volatile uint32_t IER;
+    volatile uint32_t IAR;
+    volatile uint32_t SIE;
+    volatile uint32_t CIE;
+    volatile uint32_t IVR;
+    volatile uint32_t MER;
+    volatile uint32_t IMR;
+    volatile uint32_t ILR;
+
+    // the rest is not enabled
+};
+
+IntC* intc = reinterpret_cast<IntC*>(INTC_BASE);
+Isr isrs[NIRQ] = {};
+
+}
+
+bool SetIrqEnabled(uint8_t irqn, bool enabled) {
+    uint32_t mask = 1 << irqn;
+    uint32_t ier = intc->IER;
+    bool was_enabled = (ier & (~mask)) > 0;
+    if (enabled) {
+        intc->IER = ier | mask;
+    } else {
+        intc->IER = ier & (~mask);
+    }
+
+    return was_enabled;
+}
+
+void SetIsr(uint8_t irqn, Isr isr) {
+    isrs[irqn] = isr;
+}
+
+void EnableInterrupts() {
+    intc->MER = 0x3;
+}
+
+void InterruptHandler() {
+    uint32_t ipr = intc->IPR;
+
+    for (int i = 0; i < NIRQ; i++) {
+        uint32_t mask = 1 << i;
+
+        if ((ipr & mask) > 0) {
+            // interrupt pending
+            if (isrs[i] != nullptr) {
+                isrs[i]();
+            }
+            intc->IAR = mask;  // ack
+        }
+    }
+}