add test step github ci

* Implement Maloc

* Implement Dealloc

* Migrate to a struct based heap implementation

.github/workflows/rust.yml

@@ -21,8 +21,7 @@ jobs:
       - name: Run format check
         run: cargo fmt --check
       - name: Run lint
-        run: cargo clippy -- -D warnings
+        run: cargo clippy --target aarch64-unknown-none -- -D warnings
-
   build:
     runs-on: ubuntu-latest
 
@@ -33,4 +32,16 @@ jobs:
       - name: Add AArch64 Target
         run: rustup target add aarch64-unknown-none
       - name: Build
-        run: cargo build --verbose
+        run: cargo build --verbose --target aarch64-unknown-none
+
+  test:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+      - name: Install rustfmt for nightly
+        run: rustup component add --toolchain nightly-x86_64-unknown-linux-gnu rustfmt clippy
+      - name: Add AArch64 Target
+        run: rustup target add aarch64-unknown-none
+      - name: Heap Workspace Test
+        run: cargo test -p heap

Cargo.lock

@@ -3,16 +3,37 @@
 version = 4
 
 [[package]]
-name = "NovaError"
+name = "cfg-if"
-version = "0.1.0"
+version = "1.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9330f8b2ff13f34540b44e946ef35111825727b38d33286ef986142615121801"
+
+[[package]]
+name = "getrandom"
+version = "0.3.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "899def5c37c4fd7b2664648c28120ecec138e4d395b459e5ca34f9cce2dd77fd"
+dependencies = [
+ "cfg-if",
+ "libc",
+ "r-efi",
+ "wasip2",
+]
 
 [[package]]
 name = "heap"
 version = "0.1.0"
 dependencies = [
- "NovaError",
+ "nova_error",
+ "rand",
 ]
 
+[[package]]
+name = "libc"
+version = "0.2.178"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "37c93d8daa9d8a012fd8ab92f088405fb202ea0b6ab73ee2482ae66af4f42091"
+
 [[package]]
 name = "libm"
 version = "0.2.15"
@@ -23,7 +44,125 @@ checksum = "f9fbbcab51052fe104eb5e5d351cf728d30a5be1fe14d9be8a3b097481fb97de"
 name = "nova"
 version = "0.1.0"
 dependencies = [
- "NovaError",
  "heap",
  "libm",
+ "nova_error",
+]
+
+[[package]]
+name = "nova_error"
+version = "0.1.0"
+
+[[package]]
+name = "ppv-lite86"
+version = "0.2.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "85eae3c4ed2f50dcfe72643da4befc30deadb458a9b590d720cde2f2b1e97da9"
+dependencies = [
+ "zerocopy",
+]
+
+[[package]]
+name = "proc-macro2"
+version = "1.0.103"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5ee95bc4ef87b8d5ba32e8b7714ccc834865276eab0aed5c9958d00ec45f49e8"
+dependencies = [
+ "unicode-ident",
+]
+
+[[package]]
+name = "quote"
+version = "1.0.42"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a338cc41d27e6cc6dce6cefc13a0729dfbb81c262b1f519331575dd80ef3067f"
+dependencies = [
+ "proc-macro2",
+]
+
+[[package]]
+name = "r-efi"
+version = "5.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "69cdb34c158ceb288df11e18b4bd39de994f6657d83847bdffdbd7f346754b0f"
+
+[[package]]
+name = "rand"
+version = "0.9.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6db2770f06117d490610c7488547d543617b21bfa07796d7a12f6f1bd53850d1"
+dependencies = [
+ "rand_chacha",
+ "rand_core",
+]
+
+[[package]]
+name = "rand_chacha"
+version = "0.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d3022b5f1df60f26e1ffddd6c66e8aa15de382ae63b3a0c1bfc0e4d3e3f325cb"
+dependencies = [
+ "ppv-lite86",
+ "rand_core",
+]
+
+[[package]]
+name = "rand_core"
+version = "0.9.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "99d9a13982dcf210057a8a78572b2217b667c3beacbf3a0d8b454f6f82837d38"
+dependencies = [
+ "getrandom",
+]
+
+[[package]]
+name = "syn"
+version = "2.0.111"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "390cc9a294ab71bdb1aa2e99d13be9c753cd2d7bd6560c77118597410c4d2e87"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-ident",
+]
+
+[[package]]
+name = "unicode-ident"
+version = "1.0.22"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9312f7c4f6ff9069b165498234ce8be658059c6728633667c526e27dc2cf1df5"
+
+[[package]]
+name = "wasip2"
+version = "1.0.1+wasi-0.2.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0562428422c63773dad2c345a1882263bbf4d65cf3f42e90921f787ef5ad58e7"
+dependencies = [
+ "wit-bindgen",
+]
+
+[[package]]
+name = "wit-bindgen"
+version = "0.46.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f17a85883d4e6d00e8a97c586de764dabcc06133f7f1d55dce5cdc070ad7fe59"
+
+[[package]]
+name = "zerocopy"
+version = "0.8.31"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fd74ec98b9250adb3ca554bdde269adf631549f51d8a8f8f0a10b50f1cb298c3"
+dependencies = [
+ "zerocopy-derive",
+]
+
+[[package]]
+name = "zerocopy-derive"
+version = "0.8.31"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d8a8d209fdf45cf5138cbb5a506f6b52522a25afccc534d1475dad8e31105c6a"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
 ]

Cargo.toml

@@ -15,10 +15,10 @@ panic = "abort"
 [dependencies]
 libm = "0.2.15"
 heap = {path = "heap"}
-NovaError = {path = "NovaError"}
+nova_error = {path = "nova_error"}
 
 [workspace]
 
-members = [ "NovaError",
+members = [ "nova_error",
     "heap"
 ]

README.md

@@ -2,7 +2,7 @@
 
 NovaOS is a expository project where I build a kernel from scratch for a Raspberry PI 3 B+.
 
-[Technical write-up](https://blog.leafnova.net/projects/pi3_kernel/)
+[Technical write-up](https://leafnova.net/projects/pi3_kernel/)
 
 ## Features
 

heap/Cargo.toml

@@ -4,4 +4,7 @@ version = "0.1.0"
 edition = "2024"
 
 [dependencies]
-NovaError = {path = "../NovaError"}
+nova_error = {path = "../nova_error"}
+
+[dev-dependencies]
+rand = "0.9.2"

heap/src/lib.rs

@@ -3,35 +3,28 @@
 
 use core::{
     alloc::GlobalAlloc,
-    default::Default,
     mem::size_of,
     prelude::v1::*,
-    ptr::{self, null_mut, read_volatile},
+    ptr::{self, null_mut},
     result::Result,
 };
 
-use NovaError::NovaError;
+use nova_error::NovaError;
-
-#[cfg(not(target_os = "none"))]
-extern crate std;
 
 extern crate alloc;
 
 #[repr(C, align(16))]
+#[derive(Clone, Copy)]
 pub struct HeapHeader {
-    pub next: *mut HeapHeader,
+    next: Option<*mut HeapHeader>,
-    before: *mut HeapHeader,
+    before: Option<*mut HeapHeader>,
-    pub size: usize,
+    size: usize,
     free: bool,
 }
 
 const HEAP_HEADER_SIZE: usize = size_of::<HeapHeader>();
 const MIN_BLOCK_SIZE: usize = 16;
 
-// TODO: This implementation has to be reevaluated when implementing multiprocessing
-// Spinlock could be a solution but has its issues:
-// https://matklad.github.io/2020/01/02/spinlocks-considered-harmful.html
-
 pub struct Heap {
     pub start_address: *mut HeapHeader,
     pub end_address: *mut HeapHeader,
@@ -40,8 +33,8 @@ pub struct Heap {
 impl Heap {
     pub const fn empty() -> Self {
         Self {
-            start_address: null_mut() as *mut HeapHeader,
+            start_address: null_mut(),
-            end_address: null_mut() as *mut HeapHeader,
+            end_address: null_mut(),
             raw_size: 0,
         }
     }
@@ -50,14 +43,14 @@ impl Heap {
         self.start_address = heap_start as *mut HeapHeader;
         self.end_address = heap_end as *mut HeapHeader;
 
-        self.raw_size = heap_end - heap_start;
+        self.raw_size = heap_end - heap_start + 1;
 
         unsafe {
             ptr::write(
                 self.start_address,
                 HeapHeader {
-                    next: null_mut(),
+                    next: None,
-                    before: null_mut(),
+                    before: None,
                     size: self.raw_size - HEAP_HEADER_SIZE,
                     free: true,
                 },
@@ -67,11 +60,14 @@ impl Heap {
 
     unsafe fn find_first_fit(&self, size: usize) -> Result<*mut HeapHeader, NovaError> {
         let mut current = self.start_address;
+        unsafe {
             while !fits(size, current) {
-            if (*self.start_address).next.is_null() {
+                if let Some(next) = (*current).next {
+                    current = next;
+                } else {
                     return Err(NovaError::HeapFull);
                 }
-            current = (*current).next;
+            }
         }
         Ok(current)
     }
@@ -112,43 +108,47 @@ impl Heap {
         let new_address = unsafe { current.byte_add(byte_offset) };
 
         // Handle case where fragmenting center free space
+        unsafe {
             let next = (*current).next;
-        if !(*current).next.is_null() {
+            if let Some(next) = next {
-            (*next).before = new_address;
+                (*next).before = Some(new_address);
             }
 
-        unsafe {
             ptr::write(
-                new_address as *mut HeapHeader,
+                new_address,
                 HeapHeader {
                     next,
-                    before: current,
+                    before: Some(current),
-                    size: (*current).size - size - HEAP_HEADER_SIZE,
+                    size: (*current).size - byte_offset,
                     free: true,
                 },
-            )
+            );
-        };
+
-        (*current).next = new_address;
+            (*current).next = Some(new_address);
             (*current).free = false;
             (*current).size = size;
         }
+    }
 
     pub fn free(&self, pointer: *mut u8) -> Result<(), NovaError> {
-        let mut segment = unsafe { pointer.sub(HEAP_HEADER_SIZE) as *mut HeapHeader };
+        let mut segment = Self::get_header_ref_from_data_pointer(pointer);
         unsafe {
             // IF prev is free:
             // Delete header, add size to previous and fix pointers.
             // Move Head left
-            if !(*segment).before.is_null() && (*(*segment).before).free {
+            if let Some(before_head) = (*segment).before
-                let before_head = (*segment).before;
+                && (*before_head).free
+            {
                 (*before_head).size += (*segment).size + HEAP_HEADER_SIZE;
                 delete_header(segment);
                 segment = before_head;
             }
+
             // IF next is free:
             // Delete next header and merge size, fix pointers
-            if !(*segment).next.is_null() && (*(*segment).next).free {
+            if let Some(next_head) = (*segment).next
-                let next_head = (*segment).next;
+                && (*next_head).free
+            {
                 (*segment).size += (*next_head).size + HEAP_HEADER_SIZE;
                 delete_header(next_head);
             }
@@ -159,6 +159,10 @@ impl Heap {
 
         Ok(())
     }
+
+    const fn get_header_ref_from_data_pointer(pointer: *mut u8) -> *mut HeapHeader {
+        unsafe { pointer.sub(HEAP_HEADER_SIZE) as *mut HeapHeader }
+    }
 }
 
 unsafe impl GlobalAlloc for Heap {
@@ -174,21 +178,23 @@ unsafe impl GlobalAlloc for Heap {
 unsafe impl Sync for Heap {}
 
 unsafe fn fits(size: usize, header: *mut HeapHeader) -> bool {
-    (*header).free && size <= (*header).size
+    unsafe { (*header).free && size <= (*header).size }
 }
 
 unsafe fn delete_header(header: *mut HeapHeader) {
-    let before = (*header).before;
+    unsafe {
-    let next = (*header).next;
+        let before_opt = (*header).before;
+        let next_opt = (*header).next;
 
-    if !before.is_null() {
+        if let Some(before) = before_opt {
-        (*before).next = next;
+            (*before).next = next_opt;
         }
 
-    if !next.is_null() {
+        if let Some(next) = next_opt {
-        (*next).before = before;
+            (*next).before = before_opt;
+        }
     }
 }
 
 #[cfg(test)]
-mod tests {}
+mod tests;

heap/src/tests.rs

@@ -0,0 +1,165 @@
+use super::*;
+use rand::{self, random_range};
+extern crate std;
+
+static HEAP_SIZE: usize = 1024;
+
+#[test]
+fn test_heap_allocation() {
+    let heap_vector = Box::new([0u8; HEAP_SIZE]);
+    let mut heap = Heap::empty();
+    heap.init(
+        &heap_vector[0] as *const u8 as usize,
+        &heap_vector[HEAP_SIZE - 1] as *const u8 as usize,
+    );
+
+    let root_header = heap.start_address;
+
+    let malloc_size = random_range(0..(HEAP_SIZE - HEAP_HEADER_SIZE));
+    let malloc = heap.malloc(malloc_size).unwrap();
+    let malloc_header = Heap::get_header_ref_from_data_pointer(malloc);
+
+    assert_eq!(root_header, malloc_header);
+
+    unsafe {
+        let actual_alloc_size = (*malloc_header).size;
+        let actual_raw_size = actual_alloc_size + HEAP_HEADER_SIZE;
+        // Verify sizing
+        assert!(actual_alloc_size >= malloc_size);
+        assert_eq!(actual_alloc_size % MIN_BLOCK_SIZE, 0);
+
+        // Verify section is occupied
+        assert!((*malloc_header).free == false);
+
+        // Verify next header has been created
+        let next = (*malloc_header).next.unwrap();
+
+        assert_eq!(malloc_header.byte_add(actual_raw_size), next);
+        assert!((*next).free);
+        assert_eq!((*malloc_header).next.unwrap(), next);
+        assert_eq!((*next).before.unwrap(), malloc_header);
+        assert_eq!((*next).size, HEAP_SIZE - actual_raw_size - HEAP_HEADER_SIZE)
+    }
+}
+
+#[test]
+fn test_full_heap() {
+    let heap_vector = Box::new([0u8; HEAP_SIZE]);
+    let mut heap = Heap::empty();
+    heap.init(
+        &heap_vector[0] as *const u8 as usize,
+        &heap_vector[HEAP_SIZE - 1] as *const u8 as usize,
+    );
+
+    let malloc_size = HEAP_SIZE - HEAP_HEADER_SIZE;
+    let malloc = heap.malloc(malloc_size).unwrap();
+    let malloc_header = Heap::get_header_ref_from_data_pointer(malloc);
+    unsafe {
+        assert_eq!((*malloc_header).free, false);
+        assert!((*malloc_header).next.is_none());
+    }
+
+    let malloc2 = heap.malloc(MIN_BLOCK_SIZE);
+    assert!(malloc2.is_err());
+}
+
+#[test]
+fn test_freeing_root() {
+    let heap_vector = Box::new([0u8; HEAP_SIZE]);
+    let mut heap = Heap::empty();
+    heap.init(
+        &heap_vector[0] as *const u8 as usize,
+        &heap_vector[HEAP_SIZE - 1] as *const u8 as usize,
+    );
+
+    let root_header = heap.start_address;
+    let root_header_start_size = unsafe { (*root_header).size };
+
+    let malloc_size = random_range(0..((HEAP_SIZE - HEAP_HEADER_SIZE) / 2));
+    let malloc = heap.malloc(malloc_size).unwrap();
+    let malloc_header = Heap::get_header_ref_from_data_pointer(malloc);
+    unsafe {
+        assert_eq!((*malloc_header).free, false);
+        assert!((*malloc_header).size >= malloc_size);
+        assert!((*root_header).next.is_some());
+
+        assert!(heap.free(malloc).is_ok());
+
+        assert_eq!((*root_header).size, root_header_start_size);
+        assert!((*root_header).next.is_none());
+    }
+}
+
+#[test]
+fn test_merging_free_sections() {
+    let heap_vector = Box::new([0u8; HEAP_SIZE]);
+    let mut heap = Heap::empty();
+    heap.init(
+        &heap_vector[0] as *const u8 as usize,
+        &heap_vector[HEAP_SIZE - 1] as *const u8 as usize,
+    );
+
+    let root_header = heap.start_address;
+    let root_header_start_size = unsafe { (*root_header).size };
+
+    let malloc1 = heap.malloc(MIN_BLOCK_SIZE).unwrap();
+    let malloc_header_before = unsafe { *Heap::get_header_ref_from_data_pointer(malloc1) };
+    let malloc2 = heap.malloc(MIN_BLOCK_SIZE).unwrap();
+    let _ = heap.malloc(MIN_BLOCK_SIZE).unwrap();
+
+    unsafe {
+        assert!(heap.free(malloc1).is_ok());
+
+        let malloc_header_free = *Heap::get_header_ref_from_data_pointer(malloc1);
+        assert_ne!(malloc_header_before.free, malloc_header_free.free);
+        assert_eq!(malloc_header_before.size, malloc_header_free.size);
+
+        assert!(heap.free(malloc2).is_ok());
+        let malloc_header_merge = *Heap::get_header_ref_from_data_pointer(malloc1);
+
+        assert!(malloc_header_merge.free);
+        assert_eq!(
+            malloc_header_merge.size,
+            malloc_header_free.size + MIN_BLOCK_SIZE + HEAP_HEADER_SIZE
+        );
+    }
+}
+
+#[test]
+fn test_first_fit() {
+    let heap_vector = Box::new([0u8; HEAP_SIZE]);
+    let mut heap = Heap::empty();
+    heap.init(
+        &heap_vector[0] as *const u8 as usize,
+        &heap_vector[HEAP_SIZE - 1] as *const u8 as usize,
+    );
+
+    let root_header = heap.start_address;
+    let root_header_start_size = unsafe { (*root_header).size };
+
+    let malloc1 = heap.malloc(MIN_BLOCK_SIZE).unwrap();
+    let malloc2 = heap.malloc(MIN_BLOCK_SIZE).unwrap();
+    let malloc3 = heap.malloc(MIN_BLOCK_SIZE * 3).unwrap();
+    let malloc4 = heap.malloc(MIN_BLOCK_SIZE).unwrap();
+
+    unsafe {
+        assert!(heap.free(malloc1).is_ok());
+        assert!(heap.free(malloc3).is_ok());
+        let malloc5 = heap.malloc(MIN_BLOCK_SIZE * 2).unwrap();
+        let malloc1_header = unsafe { *Heap::get_header_ref_from_data_pointer(malloc1) };
+
+        // First free block stays empty
+        assert!(malloc1_header.free);
+
+        // New allocation takes the first fit aka. malloc3
+        assert_eq!(malloc5, malloc3);
+
+        // If no free slot could be found, append to the end
+        let malloc6 = heap.malloc(MIN_BLOCK_SIZE * 2).unwrap();
+        assert!(malloc6 > malloc4);
+
+        // Malloc7 takes slot of Malloc1
+        let malloc7 = heap.malloc(MIN_BLOCK_SIZE).unwrap();
+        assert_eq!(malloc1, malloc7);
+    }
+}

nova_error/Cargo.toml

@@ -1,4 +1,4 @@
 [package]
-name = "NovaError"
+name = "nova_error"
 version = "0.1.0"
 edition = "2024"

src/configuration.rs

@@ -1,9 +1,10 @@
-static SCTLR_EL1_MMU_DISABLED: u64 = 0 << 0; //M
+static SCTLR_EL1_MMU_DISABLED: u64 = 0; //M
 static SCTLR_EL1_DATA_CACHE_DISABLED: u64 = 0 << 2; //C
 static SCTLR_EL1_INSTRUCTION_CACHE_DISABLED: u64 = 0 << 12; //I
 static SCTLR_EL1_LITTLE_ENDIAN_EL0: u64 = 0 << 24; //E0E
 static SCTLR_EL1_LITTLE_ENDIAN_EL1: u64 = 0 << 25; //EE
 
+#[allow(clippy::identity_op)]
 static SCTLR_EL1_RES: u64 = (0 << 6) | (1 << 11) | (0 << 17) | (1 << 20) | (1 << 22); //Res0 & Res1
 
 #[no_mangle]

src/framebuffer.rs

@@ -16,6 +16,7 @@ const SET_PIXEL_ORDER: u32 = 0x0004_8006;
 const GET_PITCH: u32 = 0x000_40008;
 const SET_FB_OFFSET: u32 = 0x0004_8009;
 
+#[allow(dead_code)]
 pub struct FrameBuffer {
     pixel_depth: u32, // Bits per pixel
     pitch: u32,       // Pixel per row
@@ -31,74 +32,6 @@ pub const ORANGE: u32 = 0x00FFA500;
 pub const YELLOW: u32 = 0x00FFFF00;
 
 impl FrameBuffer {
-    pub fn new() -> Self {
-        let mut mailbox = Mailbox([0; 36]);
-        mailbox.0[0] = 35 * 4;
-        mailbox.0[1] = 0;
-
-        mailbox.0[2] = SET_PHYSICAL_DISPLAY_WH;
-        mailbox.0[3] = 8;
-        mailbox.0[4] = 8;
-        mailbox.0[5] = 1920;
-        mailbox.0[6] = 1080;
-
-        mailbox.0[7] = SET_VIRTUAL_DISPLAY_WH;
-        mailbox.0[8] = 8;
-        mailbox.0[9] = 8;
-        mailbox.0[10] = 1920;
-        mailbox.0[11] = 1080;
-
-        mailbox.0[12] = SET_PIXEL_DEPTH;
-        mailbox.0[13] = 4;
-        mailbox.0[14] = 4;
-        mailbox.0[15] = 32; // 32 bit per pixel
-
-        mailbox.0[16] = SET_PIXEL_ORDER;
-        mailbox.0[17] = 4;
-        mailbox.0[18] = 4;
-        mailbox.0[19] = 0x0; // RGB
-
-        mailbox.0[20] = SET_FB_OFFSET;
-        mailbox.0[21] = 8;
-        mailbox.0[22] = 8;
-        mailbox.0[23] = 0; // X in pixels
-        mailbox.0[24] = 0; // Y in pixels
-
-        mailbox.0[25] = ALLOCATE_BUFFER;
-        mailbox.0[26] = 8;
-        mailbox.0[27] = 4;
-        mailbox.0[28] = 4096; // Alignment
-        mailbox.0[29] = 0;
-
-        mailbox.0[30] = GET_PITCH;
-        mailbox.0[31] = 4;
-        mailbox.0[32] = 0;
-        mailbox.0[33] = 0;
-
-        mailbox.0[34] = 0; // End tag
-
-        // TODO: validate responses
-
-        let addr = core::ptr::addr_of!(mailbox.0[0]) as u32;
-
-        write_mailbox(8, addr);
-
-        let _ = read_mailbox(8);
-        if mailbox.0[1] == 0 {
-            println!("Failed");
-        }
-
-        mailbox.0[28] &= 0x3FFFFFFF;
-
-        Self {
-            pixel_depth: mailbox.0[15],
-            pitch: mailbox.0[33] / (mailbox.0[15] / 8),
-            rows: mailbox.0[29] / mailbox.0[33],
-            start_addr: mailbox.0[28] as *mut u32,
-            size: mailbox.0[29],
-        }
-    }
-
     pub fn draw_pixel(&self, x: u32, y: u32, color: u32) {
         let offset = x + y * self.pitch;
         unsafe {
@@ -109,6 +42,7 @@ impl FrameBuffer {
     /*Bresenham's line algorithm
     TODO: check if its possible to optimize y1==y2 case (ARM neon?)
     */
+    #[allow(clippy::collapsible_else_if)]
     pub fn draw_line(&self, x1: u32, y1: u32, x2: u32, y2: u32, color: u32) {
         if x1 == x2 {
             for y in y1..=y2 {
@@ -218,7 +152,7 @@ impl FrameBuffer {
     }
 
     fn draw_ascii(&self, x: u32, y: u32, char: usize, scale: u32, color: u32) {
-        for (y_offset, row) in (&BASIC_LEGACY[char]).iter().enumerate() {
+        for (y_offset, row) in BASIC_LEGACY[char].iter().enumerate() {
             for bit in 0..8 {
                 match row & (1 << bit) {
                     0 => {}
@@ -241,3 +175,73 @@ impl FrameBuffer {
         }
     }
 }
+
+impl Default for FrameBuffer {
+    fn default() -> Self {
+        let mut mailbox = Mailbox([0; 36]);
+        mailbox.0[0] = 35 * 4;
+        mailbox.0[1] = 0;
+
+        mailbox.0[2] = SET_PHYSICAL_DISPLAY_WH;
+        mailbox.0[3] = 8;
+        mailbox.0[4] = 8;
+        mailbox.0[5] = 1920;
+        mailbox.0[6] = 1080;
+
+        mailbox.0[7] = SET_VIRTUAL_DISPLAY_WH;
+        mailbox.0[8] = 8;
+        mailbox.0[9] = 8;
+        mailbox.0[10] = 1920;
+        mailbox.0[11] = 1080;
+
+        mailbox.0[12] = SET_PIXEL_DEPTH;
+        mailbox.0[13] = 4;
+        mailbox.0[14] = 4;
+        mailbox.0[15] = 32; // 32 bit per pixel
+
+        mailbox.0[16] = SET_PIXEL_ORDER;
+        mailbox.0[17] = 4;
+        mailbox.0[18] = 4;
+        mailbox.0[19] = 0x0; // RGB
+
+        mailbox.0[20] = SET_FB_OFFSET;
+        mailbox.0[21] = 8;
+        mailbox.0[22] = 8;
+        mailbox.0[23] = 0; // X in pixels
+        mailbox.0[24] = 0; // Y in pixels
+
+        mailbox.0[25] = ALLOCATE_BUFFER;
+        mailbox.0[26] = 8;
+        mailbox.0[27] = 4;
+        mailbox.0[28] = 4096; // Alignment
+        mailbox.0[29] = 0;
+
+        mailbox.0[30] = GET_PITCH;
+        mailbox.0[31] = 4;
+        mailbox.0[32] = 0;
+        mailbox.0[33] = 0;
+
+        mailbox.0[34] = 0; // End tag
+
+        // TODO: validate responses
+
+        let addr = core::ptr::addr_of!(mailbox.0[0]) as u32;
+
+        write_mailbox(8, addr);
+
+        let _ = read_mailbox(8);
+        if mailbox.0[1] == 0 {
+            println!("Failed");
+        }
+
+        mailbox.0[28] &= 0x3FFFFFFF;
+
+        Self {
+            pixel_depth: mailbox.0[15],
+            pitch: mailbox.0[33] / (mailbox.0[15] / 8),
+            rows: mailbox.0[29] / mailbox.0[33],
+            start_addr: mailbox.0[28] as *mut u32,
+            size: mailbox.0[29],
+        }
+    }
+}

src/irq_interrupt.rs

@@ -6,7 +6,6 @@ use core::{
 use crate::{
     mmio_read, mmio_write,
     peripherals::gpio::{blink_gpio, SpecificGpio},
-    print,
     timer::sleep_s,
 };
 
@@ -54,7 +53,7 @@ fn esr_uart_dump() {
     let esr: u32;
     unsafe {
         asm!(
-            "mrs {esr}, ESR_EL1",
+            "mrs {esr:x}, ESR_EL1",
             esr = out(reg) esr
         );
     }
@@ -80,6 +79,7 @@ fn handle_gpio_interrupt() {
         let val = read_gpio_event_detect_status(i);
 
         if val {
+            #[allow(clippy::single_match)]
             match i {
                 26 => print!("Button Pressed"),
                 _ => {}

src/lib.rs

@@ -1,5 +1,5 @@
 #![no_std]
-
+#![allow(clippy::missing_safety_doc)]
 use core::{
     panic::PanicInfo,
     ptr::{read_volatile, write_volatile},
@@ -19,7 +19,8 @@ pub unsafe fn init_heap() {
     let start = core::ptr::addr_of_mut!(__heap_start) as usize;
     let end = core::ptr::addr_of_mut!(__heap_end) as usize;
 
-    GLOBAL_ALLOCATOR.init(start, end);
+    let heap = core::ptr::addr_of_mut!(GLOBAL_ALLOCATOR);
+    (*heap).init(start, end);
 }
 
 #[panic_handler]

src/mailbox.rs

@@ -1,9 +1,10 @@
 use crate::{mmio_read, mmio_write};
+use nova_error::NovaError;
 
 const MBOX_BASE: u32 = 0x3F00_0000 + 0xB880;
 
 // MB0
-const MBOX_READ: u32 = MBOX_BASE + 0x00;
+const MBOX_READ: u32 = MBOX_BASE;
 const MBOX_STATUS: u32 = MBOX_BASE + 0x18;
 
 // MB1
@@ -29,7 +30,7 @@ macro_rules! mailbox_command {
         /// More information at: https://github.com/raspberrypi/firmware/wiki/Mailbox-property-interface
         pub fn $name(
             request_data: [u32; $request_len / 4],
-        ) -> Result<[u32; $response_len / 4], NovaError::NovaError> {
+        ) -> Result<[u32; $response_len / 4], NovaError> {
             let mut mailbox =
                 [0u32; (HEADER_LENGTH + max!($request_len, $response_len) + FOOTER_LENGTH) / 4];
             mailbox[0] = (HEADER_LENGTH + max!($request_len, $response_len) + FOOTER_LENGTH) as u32; // Total length in Bytes
@@ -48,7 +49,7 @@ macro_rules! mailbox_command {
             let _ = read_mailbox(8);
 
             if mailbox[1] == 0 {
-                return Err(NovaError::NovaError::Mailbox);
+                return Err(NovaError::Mailbox);
             }
 
             let mut out = [0u32; $response_len / 4];

src/main.rs

@@ -2,6 +2,7 @@
 #![no_std]
 #![feature(asm_experimental_arch)]
 #![allow(static_mut_refs)]
+#![allow(clippy::missing_safety_doc)]
 use core::{
     arch::{asm, global_asm},
     ptr::write_volatile,
@@ -9,6 +10,7 @@ use core::{
 
 extern crate alloc;
 
+use alloc::boxed::Box;
 use nova::{
     framebuffer::{FrameBuffer, BLUE, GREEN, RED},
     init_heap,
@@ -23,7 +25,6 @@ use nova::{
     },
     print, println,
     timer::{delay_nops, sleep_us},
-    GLOBAL_ALLOCATOR,
 };
 
 global_asm!(include_str!("vector.S"));
@@ -94,7 +95,7 @@ pub extern "C" fn kernel_main() -> ! {
     gpio_pull_up(26);
     set_falling_edge_detect(26, true);
 
-    let fb = FrameBuffer::new();
+    let fb = FrameBuffer::default();
 
     fb.draw_square(500, 500, 600, 700, RED);
     fb.draw_square_fill(800, 800, 900, 900, GREEN);
@@ -113,13 +114,8 @@ pub extern "C" fn kernel_main() -> ! {
 }
 
 unsafe fn heap_test() {
-    let a = GLOBAL_ALLOCATOR.malloc(32).unwrap();
+    let b = Box::new([1, 2, 3, 4]);
-    let b = GLOBAL_ALLOCATOR.malloc(64).unwrap();
+    println!("{:?}", b);
-    let c = GLOBAL_ALLOCATOR.malloc(128).unwrap();
-    let _ = GLOBAL_ALLOCATOR.malloc(256).unwrap();
-    GLOBAL_ALLOCATOR.free(b).unwrap();
-    GLOBAL_ALLOCATOR.free(a).unwrap();
-    GLOBAL_ALLOCATOR.free(c).unwrap();
 }
 
 fn cos(x: u32) -> f64 {