From 4963a90268fb4b0fa8953cc60042784be51b7ea5 Mon Sep 17 00:00:00 2001
From: ga <ga@oldell.fish>
Date: Mon, 22 Mar 2021 18:27:24 +0000
Subject: [PATCH] Merge branch 'fix-irq-handling' of
 https://github.com/vintagepc/simavr Upstream pull request #415: Fix TOV/ICR
 handling, SEI delay with corrections to timer code and addition of minimal
 test code.

---
 simavr/sim/avr_timer.c         | 30 ++++++++++++++++--------------
 simavr/sim/sim_core.h          |  2 +-
 tests/atmega48_enabled_timer.c | 30 +++++++++++++++++++++++++-----
 3 files changed, 42 insertions(+), 20 deletions(-)

diff --git a/simavr/sim/avr_timer.c b/simavr/sim/avr_timer.c
index f85b884..5d52c5e 100644
--- a/simavr/sim/avr_timer.c
+++ b/simavr/sim/avr_timer.c
@@ -716,23 +716,25 @@ avr_timer_write_pending(
 		void * param)
 {
 	avr_timer_t * p = (avr_timer_t *)param;
-	// save old bits values
-	uint8_t ov = avr_regbit_get(avr, p->overflow.raised);
-	uint8_t ic = avr_regbit_get(avr, p->icr.raised);
-	uint8_t cp[AVR_TIMER_COMP_COUNT];
 
-	for (int compi = 0; compi < AVR_TIMER_COMP_COUNT; compi++)
-		cp[compi] = avr_regbit_get(avr, p->comp[compi].interrupt.raised);
+	// All bits in this register are assumed to be write-1-to-clear.
 
-	// write the value
-	// avr_core_watch_write(avr, addr, v); // This raises flags instead of clearing it.
-
-	// clear any interrupts & flags
-	avr_clear_interrupt_if(avr, &p->overflow, ov);
-	avr_clear_interrupt_if(avr, &p->icr, ic);
+	if (addr == p->overflow.raised.reg &&
+	    avr_regbit_from_value(avr, p->overflow.raised, v)) {
+		avr_clear_interrupt(avr, &p->overflow);
+	}
+	if (addr == p->icr.raised.reg &&
+	    avr_regbit_from_value(avr, p->icr.raised, v)) {
+		avr_clear_interrupt(avr, &p->icr);
+	}
 
-	for (int compi = 0; compi < AVR_TIMER_COMP_COUNT; compi++)
-		avr_clear_interrupt_if(avr, &p->comp[compi].interrupt, cp[compi]);
+	for (int compi = 0; compi < AVR_TIMER_COMP_COUNT; compi++) {
+		if (addr == p->comp[compi].interrupt.raised.reg &&
+		    avr_regbit_from_value(avr, p->comp[compi].interrupt.raised,
+					  v)) {
+			avr_clear_interrupt(avr, &p->comp[compi].interrupt);
+		}
+	}
 }
 
 static void
diff --git a/simavr/sim/sim_core.h b/simavr/sim/sim_core.h
index 403c119..992c068 100644
--- a/simavr/sim/sim_core.h
+++ b/simavr/sim/sim_core.h
@@ -113,7 +113,7 @@ static inline void avr_sreg_set(avr_t * avr, uint8_t flag, uint8_t ival)
 	if (flag == S_I) {
 		if (ival) {
 			if (!avr->sreg[S_I])
-				avr->interrupt_state = -2;
+				avr->interrupt_state = -1;
 		} else
 			avr->interrupt_state = 0;
 	}
diff --git a/tests/atmega48_enabled_timer.c b/tests/atmega48_enabled_timer.c
index 04b8db4..527e44a 100644
--- a/tests/atmega48_enabled_timer.c
+++ b/tests/atmega48_enabled_timer.c
@@ -14,8 +14,11 @@
 #include "avr_mcu_section.h"
 AVR_MCU(F_CPU, "atmega48");
 
+volatile uint8_t count;
+
 ISR(TIMER0_COMPA_vect)
 {
+    ++count;
 }
 
 int main(void)
@@ -27,13 +30,30 @@ int main(void)
 
 	TCCR0B |= (1 << CS00) | (1 << CS01);        // Start timer: clk/64
 
+	while ((TIFR0 & (1 << OCF0A)) == 0)
+		;
+
+	// Now interrupt is pending.  Try and clear it.
+
+	TIFR0 = 0;
+	if (TIFR0 & (1 << OCF0A))
+		++count;			    // Should not clear
+	TIFR0 = (1 << OCF0A);
+	if ((TIFR0 & (1 << OCF0A)) == 0)
+		++count;			    // Should clear!
+
 	sei();                                      // Enable global interrupts
 
-	// here the interupts are enabled, but the interupt
-	// vector should not be called
-	sleep_mode();
+	// Let it run to next interrupt.
 
-	// this should not be reached
-	cli();
 	sleep_mode();
+	TIMSK0 = 0;		                    // Disable CTC interrupt
+
+	if (count == 3)				    // Expected
+		cli();
+
+	// Time out if interrupting or count wrong.
+
+	for (;;)
+		sleep_mode();
 }
-- 
2.39.5