From d8ee65b873c38dc02c63e5c64bd5eec4648d594a Mon Sep 17 00:00:00 2001
From: ondra05 <ondra@ondra05.cz>
Date: Tue, 11 Jul 2023 10:29:23 +0200
Subject: [PATCH 1/4] Implement timer

---
 hbvm/src/main.rs   |  2 +-
 hbvm/src/vm/mod.rs | 26 ++++++++++++++++++++++----
 2 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/hbvm/src/main.rs b/hbvm/src/main.rs
index 255384e8..5f9b27f0 100644
--- a/hbvm/src/main.rs
+++ b/hbvm/src/main.rs
@@ -18,7 +18,7 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
         return Ok(());
     } else {
         unsafe {
-            let mut vm = Vm::new_unchecked(&prog, TestTrapHandler);
+            let mut vm = Vm::<_, 0>::new_unchecked(&prog, TestTrapHandler);
             vm.memory.insert_test_page();
             println!("Program interrupt: {:?}", vm.run());
             println!("{:?}", vm.registers);
diff --git a/hbvm/src/vm/mod.rs b/hbvm/src/vm/mod.rs
index 0f6fa2f0..65281611 100644
--- a/hbvm/src/vm/mod.rs
+++ b/hbvm/src/vm/mod.rs
@@ -79,7 +79,7 @@ macro_rules! cond_jump {
 }
 
 /// HoleyBytes Virtual Machine
-pub struct Vm<'a, T> {
+pub struct Vm<'a, T, const TIMER_QUOTIENT: usize> {
     /// Holds 256 registers
     ///
     /// Writing to register 0 is considered undefined behaviour
@@ -97,9 +97,12 @@ pub struct Vm<'a, T> {
 
     /// Program
     program: &'a [u8],
+
+    /// Program timer
+    timer: usize,
 }
 
-impl<'a, T: HandleTrap> Vm<'a, T> {
+impl<'a, T: HandleTrap, const TIMER_QUOTIENT: usize> Vm<'a, T, TIMER_QUOTIENT> {
     /// Create a new VM with program and trap handler
     ///
     /// # Safety
@@ -111,6 +114,7 @@ impl<'a, T: HandleTrap> Vm<'a, T> {
             traph,
             pc: 0,
             program,
+            timer: 0,
         }
     }
 
@@ -123,12 +127,19 @@ impl<'a, T: HandleTrap> Vm<'a, T> {
     /// Execute program
     ///
     /// Program can return [`VmRunError`] if a trap handling failed
-    pub fn run(&mut self) -> Result<(), VmRunError> {
+    pub fn run(&mut self) -> Result<VmRunOk, VmRunError> {
         use hbbytecode::opcode::*;
         loop {
             // Fetch instruction
             let Some(&opcode) = self.program.get(self.pc)
-                else { return Ok(()) };
+                else { return Ok(VmRunOk::End) };
+
+            if TIMER_QUOTIENT != 0 {
+                self.timer += 1;
+                if self.timer % TIMER_QUOTIENT == 0 {
+                    return Ok(VmRunOk::Timer);
+                }
+            }
 
             // Big match
             unsafe {
@@ -350,3 +361,10 @@ pub enum VmRunError {
     /// Unhandled store access exception
     StoreAccessEx(u64),
 }
+
+/// Virtual machine halt ok
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum VmRunOk {
+    End,
+    Timer,
+}

From 9c93a0fa8f3241c89478d1b75838f119e3b89346 Mon Sep 17 00:00:00 2001
From: ondra05 <ondra@ondra05.cz>
Date: Tue, 11 Jul 2023 10:31:03 +0200
Subject: [PATCH 2/4] wrap around timer

---
 hbvm/src/vm/mod.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hbvm/src/vm/mod.rs b/hbvm/src/vm/mod.rs
index 65281611..8505ff1f 100644
--- a/hbvm/src/vm/mod.rs
+++ b/hbvm/src/vm/mod.rs
@@ -135,7 +135,7 @@ impl<'a, T: HandleTrap, const TIMER_QUOTIENT: usize> Vm<'a, T, TIMER_QUOTIENT> {
                 else { return Ok(VmRunOk::End) };
 
             if TIMER_QUOTIENT != 0 {
-                self.timer += 1;
+                self.timer = self.timer.wrapping_add(1);
                 if self.timer % TIMER_QUOTIENT == 0 {
                     return Ok(VmRunOk::Timer);
                 }

From 32b63c0f23fef74125abc72597b1689169273232 Mon Sep 17 00:00:00 2001
From: ondra05 <ondra@ondra05.cz>
Date: Tue, 11 Jul 2023 10:32:26 +0200
Subject: [PATCH 3/4] Moved

---
 hbvm/src/vm/mod.rs | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/hbvm/src/vm/mod.rs b/hbvm/src/vm/mod.rs
index 8505ff1f..4997c5a6 100644
--- a/hbvm/src/vm/mod.rs
+++ b/hbvm/src/vm/mod.rs
@@ -134,13 +134,6 @@ impl<'a, T: HandleTrap, const TIMER_QUOTIENT: usize> Vm<'a, T, TIMER_QUOTIENT> {
             let Some(&opcode) = self.program.get(self.pc)
                 else { return Ok(VmRunOk::End) };
 
-            if TIMER_QUOTIENT != 0 {
-                self.timer = self.timer.wrapping_add(1);
-                if self.timer % TIMER_QUOTIENT == 0 {
-                    return Ok(VmRunOk::Timer);
-                }
-            }
-
             // Big match
             unsafe {
                 match opcode {
@@ -329,6 +322,13 @@ impl<'a, T: HandleTrap, const TIMER_QUOTIENT: usize> Vm<'a, T, TIMER_QUOTIENT> {
                     }
                 }
             }
+
+            if TIMER_QUOTIENT != 0 {
+                self.timer = self.timer.wrapping_add(1);
+                if self.timer % TIMER_QUOTIENT == 0 {
+                    return Ok(VmRunOk::Timer);
+                }
+            }
         }
     }
 

From e7c014f6e4365fef41914a0b62738957789b2c5e Mon Sep 17 00:00:00 2001
From: ondra05 <ondra@ondra05.cz>
Date: Tue, 11 Jul 2023 10:33:55 +0200
Subject: [PATCH 4/4] doc

---
 hbvm/src/vm/mod.rs | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/hbvm/src/vm/mod.rs b/hbvm/src/vm/mod.rs
index 4997c5a6..182b574d 100644
--- a/hbvm/src/vm/mod.rs
+++ b/hbvm/src/vm/mod.rs
@@ -365,6 +365,9 @@ pub enum VmRunError {
 /// Virtual machine halt ok
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 pub enum VmRunOk {
+    /// Program has eached its end
     End,
+
+    /// Program was interrupted by a timer
     Timer,
 }