feat: make the stack grow from 0x3000 to 0xFFFF

IDEAS.md

@@ -67,36 +67,23 @@ R14: 0x0E
   Stores the status flags of the program execution.
 ```
 
-### Base Memory Layout
+### 04. Memory Layout
 
 ```
 0x0000 - 0x1000
   Code Segment: `text`
   Stores the program instructions.
   Read-only.
 
-0x1000 - 0x2000
-  Initialized Data Segment: `data`
-  Contains the variables initialized in the code.
-  TODO: const variables should be read-only. needs separate sections.
-
-0x2000 - 0x3000
-  Uninitialized Data Segment: `bss`
-  Initializes to zero.
-  Contains all global variables that are initialized to zero, or do not have an explicit initialization in code, such as `int i`
+0x1000 - 0x3000
+  Read-only data, which is not code.
 
 after 0x3000
-  Heap.
-  Contains all dynamically allocated memory.
-  Grows to larger addresses.
-  Use malloc, realloc and free.
-
-below 0xFFFF
-  Stack.
-  Stack is LIFO.
-  Contains the program stack frames.
-  Stack frames contain the local variables of the function.
-  Makes recursion possible.
+  Stack, LIFO.
   SP tracks the top of the stack.
-  Grows downwards.
+  Grows to 0xFFFF.
 ```
+
+## 05. Stack Frames
+
+- Stack frames contain the local variables of the function call.

src/mem/memory.rs

@@ -1,4 +1,4 @@
-use crate::mem::MAX_STACK_ADDR;
+use crate::MIN_STACK_ADDR;
 
 pub const MEMORY_SIZE: u16 = 0xFFFF;
 
@@ -38,7 +38,7 @@ impl Memory {
     }
 
     pub fn read_stack(&self, count: u16) -> Vec<u16> {
-        self.read(MAX_STACK_ADDR - count, count)
+        self.read(MIN_STACK_ADDR, count)
     }
 }
 

src/mem/stack.rs

@@ -28,12 +28,12 @@ impl<'a> StackManager<'a> {
     }
 
     pub fn push(&mut self, val: u16) -> Result<(), Whatever> {
-        if self.top() < MIN_STACK_ADDR {
+        if self.top() > MAX_STACK_ADDR {
             whatever!("stack overflow")
         }
 
-        // Decrement the stack pointer.
-        self.reg.dec(SP);
+        // Increment the stack pointer.
+        self.reg.inc(SP);
 
         // Save the value at the top of the stack.
         self.write(val);
@@ -50,15 +50,17 @@ impl<'a> StackManager<'a> {
     }
 
     pub fn pop(&mut self) -> Result<u16, Whatever> {
-        if self.top() > MAX_STACK_ADDR {
+        if self.top() < MIN_STACK_ADDR {
             whatever!("stack underflow")
         }
 
         let v = self.peek();
+
+        // Clear the value at the top of the stack.
         self.write(0);
 
-        // Increment the stack pointer.
-        self.reg.inc(SP);
+        // Decrement the stack pointer.
+        self.reg.dec(SP);
 
         // Return the value at the top of the stack.
         Ok(v)

src/register/mod.rs

@@ -1,4 +1,4 @@
-use crate::mem::MAX_STACK_ADDR;
+use crate::MIN_STACK_ADDR;
 use crate::register::Register::{PC, SP};
 
 const REG_COUNT: usize = 0xF;
@@ -28,7 +28,7 @@ impl Registers {
 
         // Initialize the stack pointer.
         v.set(PC, 0);
-        v.set(SP, MAX_STACK_ADDR);
+        v.set(SP, MIN_STACK_ADDR);
 
         v
     }

tests/math.rs

@@ -10,15 +10,15 @@ mod tests {
 
         m.tick();
         m.tick();
-        assert_eq!(m.mem.read_stack(3), [0, 10, 5]);
+        assert_eq!(m.mem.read_stack(3), [0, 5, 10]);
 
         m.tick();
-        assert_eq!(m.mem.read_stack(3), [0, 0, 15]);
+        assert_eq!(m.mem.read_stack(3), [0, 15, 0]);
 
         m.tick();
         assert_eq!(m.stack().peek(), 3);
 
         m.tick();
-        assert_eq!(m.mem.read_stack(3), [0, 0, 12]);
+        assert_eq!(m.mem.read_stack(3), [0, 12, 0]);
     }
 }

tests/strings.rs

@@ -22,7 +22,7 @@ mod tests {
         assert_eq!(m.mem.read_stack(5), [0, 0, 0, 0, 0]);
 
         m.run();
-        assert_eq!(m.mem.read_stack(5), [111, 108, 108, 101, 104]);
+        assert_eq!(m.mem.read_stack(6), [0, 104, 101, 108, 108, 111]);
     }
 
     #[test]
@@ -50,6 +50,6 @@ mod tests {
         let s_addr = ms.add_str("poom");
         m.mem.load_code(vec![I::LoadString(s_addr)]);
         m.tick();
-        assert_eq!(m.mem.read_stack(5), [0, 109, 111, 111, 112]);
+        assert_eq!(m.mem.read_stack(5), [0, 112, 111, 111, 109]);
     }
 }