From d18d41fc0280335587f39b0d03f640177c766a09 Mon Sep 17 00:00:00 2001
From: Paul Mathieu <paul@ponteilla.net>
Date: Tue, 24 Jun 2025 23:02:38 -0700
Subject: [PATCH] mbv: small refactor interrupts

---
 mbv/apps/timer/timer.cc |  9 +++++----
 mbv/apps/uart/uart.cc   |  9 +++++----
 mbv/hal/intc.cc         |  6 +++++-
 mbv/hal/intc.h          |  4 ++++
 mbv/hal/interrupts.cc   | 28 +++++++++++++++++++++-------
 mbv/hal/interrupts.h    |  3 +++
 6 files changed, 43 insertions(+), 16 deletions(-)

diff --git a/mbv/apps/timer/timer.cc b/mbv/apps/timer/timer.cc
index 1c97a76..c8159b4 100644
--- a/mbv/apps/timer/timer.cc
+++ b/mbv/apps/timer/timer.cc
@@ -25,9 +25,8 @@ void SetupTimer() {
     timer->SetupAsWdt(100'000'000);
     timer->EnableT1();
 
-    SetIsr(TIMER0_IRQN, Timer0Isr);
-    SetIrqEnabled(TIMER0_IRQN, true);
-    EnableInterrupts();
+    intc::SetIsr(TIMER0_IRQN, Timer0Isr);
+    intc::SetIrqEnabled(TIMER0_IRQN, true);
 }
 
 }  // namespace
@@ -37,8 +36,10 @@ int main() {
     leds->data = 0xa0;
 
     SetupTimer();
-    SetExternalInterruptHandler(InterruptHandler);
+    intc::EnableInterrupts();
+    SetExternalInterruptHandler(intc::InterruptHandler);
     EnableExternalInterrupts();
+    EnableInterrupts(true);
 
     leds->data = 0xa1;
 
diff --git a/mbv/apps/uart/uart.cc b/mbv/apps/uart/uart.cc
index 1e0da91..e962709 100644
--- a/mbv/apps/uart/uart.cc
+++ b/mbv/apps/uart/uart.cc
@@ -41,8 +41,8 @@ void InitUarts() {
     XUartLite_SetRecvHandler(uart0, HandleUartRxFromIsr, nullptr);
     XUartLite_EnableInterrupt(uart0);
 
-    SetIsr(UART0_IRQN, Uart0Isr);
-    SetIrqEnabled(UART0_IRQN, true);
+    intc::SetIsr(UART0_IRQN, Uart0Isr);
+    intc::SetIrqEnabled(UART0_IRQN, true);
 }
 
 }  // namespace
@@ -52,9 +52,10 @@ int main() {
     leds->data = 0xa0;
 
     InitUarts();
-    EnableInterrupts();
-    SetExternalInterruptHandler(InterruptHandler);
+    intc::EnableInterrupts();
+    SetExternalInterruptHandler(intc::InterruptHandler);
     EnableExternalInterrupts();
+    EnableInterrupts(true);
 
     int counter = 0;
 
diff --git a/mbv/hal/intc.cc b/mbv/hal/intc.cc
index fe13989..48a175b 100644
--- a/mbv/hal/intc.cc
+++ b/mbv/hal/intc.cc
@@ -1,7 +1,9 @@
 #include "intc.h"
 
+// this interrupt controller is tied to the pol0 design
 #include "pol0.h"
 
+namespace intc {
 namespace {
 
 struct IntC {
@@ -22,7 +24,7 @@ struct IntC {
 IntC* intc = reinterpret_cast<IntC*>(INTC_BASE);
 Isr isrs[NIRQ] = {};
 
-}
+}  // namespace
 
 bool SetIrqEnabled(uint8_t irqn, bool enabled) {
     uint32_t mask = 1 << irqn;
@@ -60,3 +62,5 @@ void InterruptHandler() {
         }
     }
 }
+
+}  // namespace intc
diff --git a/mbv/hal/intc.h b/mbv/hal/intc.h
index 156af0e..7e463ec 100644
--- a/mbv/hal/intc.h
+++ b/mbv/hal/intc.h
@@ -2,6 +2,8 @@
 
 #include <cstdint>
 
+namespace intc {
+
 using Isr = void(*)(void);
 
 /// Returns: true if the IRQ was previously enabled
@@ -14,3 +16,5 @@ void EnableInterrupts();
 
 // Feed this to the CPU's interrupt handler
 void InterruptHandler();
+
+}  // namespace intc
diff --git a/mbv/hal/interrupts.cc b/mbv/hal/interrupts.cc
index a9d777d..c4a7df5 100644
--- a/mbv/hal/interrupts.cc
+++ b/mbv/hal/interrupts.cc
@@ -1,5 +1,6 @@
 #include <cstdint>
 
+#include "bios.h"
 #include "interrupts.h"
 
 namespace {
@@ -26,27 +27,40 @@ void TrapHandler() {
 
         mip &= ~(kMieExternalInterruptMask);
         asm volatile("csrw mip, %0" :: "r"(mip));
+    } else {
+        BiosWozmon();
     }
 }
 
-}
+}  // namespace
 
 void SetExternalInterruptHandler(Isr handler) {
     external_handler = handler;
 }
 
 void EnableExternalInterrupts() {
-    uint32_t mstatus;
     uint32_t mie;
     Isr trap = TrapHandler;
 
-    asm volatile("csrr %0, mstatus" : "=r"(mstatus));
     asm volatile("csrr %0, mie" : "=r"(mie));
-
     asm volatile("csrw mtvec, %0" :: "r"(trap));
-
     mie |= kMieExternalInterruptMask;
     asm volatile("csrw mie, %0" :: "r"(mie));
-    mstatus |= kMstatusMieMask;
-    asm volatile("csrw mstatus, %0" :: "r"(mstatus));
+}
+
+bool EnableInterrupts(bool on) {
+    uint32_t mstatus;
+    bool was_on;
+    asm volatile("csrr %0, mstatus" : "=r"(mstatus));
+
+    was_on = (mstatus & kMstatusMieMask) > 0;
+
+    if (on) {
+        mstatus |= kMstatusMieMask;
+    } else {
+        mstatus &= ~kMstatusMieMask;
+    }
+
+    asm volatile("csrw mstatus, %0" :: "r"(mstatus));
+    return was_on;
 }
diff --git a/mbv/hal/interrupts.h b/mbv/hal/interrupts.h
index ec09d51..66ec20f 100644
--- a/mbv/hal/interrupts.h
+++ b/mbv/hal/interrupts.h
@@ -4,3 +4,6 @@ using Isr = void(*)();
 
 void SetExternalInterruptHandler(Isr handler);
 void EnableExternalInterrupts();
+
+/** Returns true if interrupts were enabled, false otherwise */
+bool EnableInterrupts(bool on);