Housekeeping

05_safe_globals/README.md

@@ -55,7 +55,7 @@ make qemu
 diff -uNr 04_zero_overhead_abstraction/src/arch/aarch64/sync.rs 05_safe_globals/src/arch/aarch64/sync.rs
 --- 04_zero_overhead_abstraction/src/arch/aarch64/sync.rs
 +++ 05_safe_globals/src/arch/aarch64/sync.rs
-@@ -0,0 +1,44 @@
+@@ -0,0 +1,52 @@
 +// SPDX-License-Identifier: MIT
 +//
 +// Copyright (c) 2018-2019 Andre Richter <andre.o.richter@gmail.com>
@@ -65,6 +65,10 @@ diff -uNr 04_zero_overhead_abstraction/src/arch/aarch64/sync.rs 05_safe_globals/
 +use crate::interface;
 +use core::cell::UnsafeCell;
 +
++//--------------------------------------------------------------------------------------------------
++// Arch-public
++//--------------------------------------------------------------------------------------------------
++
 +/// A pseudo-lock for teaching purposes.
 +///
 +/// Used to introduce [interior mutability].
@@ -91,6 +95,10 @@ diff -uNr 04_zero_overhead_abstraction/src/arch/aarch64/sync.rs 05_safe_globals/
 +    }
 +}
 +
++//--------------------------------------------------------------------------------------------------
++// OS interface implementations
++//--------------------------------------------------------------------------------------------------
++
 +impl<T> interface::sync::Mutex for &NullLock<T> {
 +    type Data = T;
 +

05_safe_globals/src/arch/aarch64/sync.rs

@@ -7,6 +7,10 @@
 use crate::interface;
 use core::cell::UnsafeCell;
 
+//--------------------------------------------------------------------------------------------------
+// Arch-public
+//--------------------------------------------------------------------------------------------------
+
 /// A pseudo-lock for teaching purposes.
 ///
 /// Used to introduce [interior mutability].
@@ -33,6 +37,10 @@ impl<T> NullLock<T> {
     }
 }
 
+//--------------------------------------------------------------------------------------------------
+// OS interface implementations
+//--------------------------------------------------------------------------------------------------
+
 impl<T> interface::sync::Mutex for &NullLock<T> {
     type Data = T;
 

06_drivers_gpio_uart/src/arch/aarch64/sync.rs

@@ -7,6 +7,10 @@
 use crate::interface;
 use core::cell::UnsafeCell;
 
+//--------------------------------------------------------------------------------------------------
+// Arch-public
+//--------------------------------------------------------------------------------------------------
+
 /// A pseudo-lock for teaching purposes.
 ///
 /// Used to introduce [interior mutability].
@@ -33,6 +37,10 @@ impl<T> NullLock<T> {
     }
 }
 
+//--------------------------------------------------------------------------------------------------
+// OS interface implementations
+//--------------------------------------------------------------------------------------------------
+
 impl<T> interface::sync::Mutex for &NullLock<T> {
     type Data = T;
 

07_uart_chainloader/src/arch/aarch64/sync.rs

@@ -7,6 +7,10 @@
 use crate::interface;
 use core::cell::UnsafeCell;
 
+//--------------------------------------------------------------------------------------------------
+// Arch-public
+//--------------------------------------------------------------------------------------------------
+
 /// A pseudo-lock for teaching purposes.
 ///
 /// Used to introduce [interior mutability].
@@ -33,6 +37,10 @@ impl<T> NullLock<T> {
     }
 }
 
+//--------------------------------------------------------------------------------------------------
+// OS interface implementations
+//--------------------------------------------------------------------------------------------------
+
 impl<T> interface::sync::Mutex for &NullLock<T> {
     type Data = T;
 

08_timestamps/README.md

@@ -100,7 +100,7 @@ diff -uNr 07_uart_chainloader/Makefile 08_timestamps/Makefile
 diff -uNr 07_uart_chainloader/src/arch/aarch64/time.rs 08_timestamps/src/arch/aarch64/time.rs
 --- 07_uart_chainloader/src/arch/aarch64/time.rs
 +++ 08_timestamps/src/arch/aarch64/time.rs
-@@ -0,0 +1,77 @@
+@@ -0,0 +1,85 @@
 +// SPDX-License-Identifier: MIT
 +//
 +// Copyright (c) 2018-2019 Andre Richter <andre.o.richter@gmail.com>
@@ -113,8 +113,16 @@ diff -uNr 07_uart_chainloader/src/arch/aarch64/time.rs 08_timestamps/src/arch/aa
 +
 +const NS_PER_S: u64 = 1_000_000_000;
 +
++//--------------------------------------------------------------------------------------------------
++// Arch-public
++//--------------------------------------------------------------------------------------------------
++
 +pub struct Timer;
 +
++//--------------------------------------------------------------------------------------------------
++// OS interface implementations
++//--------------------------------------------------------------------------------------------------
++
 +impl interface::time::Timer for Timer {
 +    fn resolution(&self) -> Duration {
 +        Duration::from_nanos(NS_PER_S / (CNTFRQ_EL0.get() as u64))

08_timestamps/src/arch/aarch64/sync.rs

@@ -7,6 +7,10 @@
 use crate::interface;
 use core::cell::UnsafeCell;
 
+//--------------------------------------------------------------------------------------------------
+// Arch-public
+//--------------------------------------------------------------------------------------------------
+
 /// A pseudo-lock for teaching purposes.
 ///
 /// Used to introduce [interior mutability].
@@ -33,6 +37,10 @@ impl<T> NullLock<T> {
     }
 }
 
+//--------------------------------------------------------------------------------------------------
+// OS interface implementations
+//--------------------------------------------------------------------------------------------------
+
 impl<T> interface::sync::Mutex for &NullLock<T> {
     type Data = T;
 

08_timestamps/src/arch/aarch64/time.rs

@@ -10,8 +10,16 @@ use cortex_a::regs::*;
 
 const NS_PER_S: u64 = 1_000_000_000;
 
+//--------------------------------------------------------------------------------------------------
+// Arch-public
+//--------------------------------------------------------------------------------------------------
+
 pub struct Timer;
 
+//--------------------------------------------------------------------------------------------------
+// OS interface implementations
+//--------------------------------------------------------------------------------------------------
+
 impl interface::time::Timer for Timer {
     fn resolution(&self) -> Duration {
         Duration::from_nanos(NS_PER_S / (CNTFRQ_EL0.get() as u64))

09_hw_debug_JTAG/src/arch/aarch64/sync.rs

@@ -7,6 +7,10 @@
 use crate::interface;
 use core::cell::UnsafeCell;
 
+//--------------------------------------------------------------------------------------------------
+// Arch-public
+//--------------------------------------------------------------------------------------------------
+
 /// A pseudo-lock for teaching purposes.
 ///
 /// Used to introduce [interior mutability].
@@ -33,6 +37,10 @@ impl<T> NullLock<T> {
     }
 }
 
+//--------------------------------------------------------------------------------------------------
+// OS interface implementations
+//--------------------------------------------------------------------------------------------------
+
 impl<T> interface::sync::Mutex for &NullLock<T> {
     type Data = T;
 

09_hw_debug_JTAG/src/arch/aarch64/time.rs

@@ -10,8 +10,16 @@ use cortex_a::regs::*;
 
 const NS_PER_S: u64 = 1_000_000_000;
 
+//--------------------------------------------------------------------------------------------------
+// Arch-public
+//--------------------------------------------------------------------------------------------------
+
 pub struct Timer;
 
+//--------------------------------------------------------------------------------------------------
+// OS interface implementations
+//--------------------------------------------------------------------------------------------------
+
 impl interface::time::Timer for Timer {
     fn resolution(&self) -> Duration {
         Duration::from_nanos(NS_PER_S / (CNTFRQ_EL0.get() as u64))

10_privilege_level/README.md

@@ -213,7 +213,7 @@ make chainbot
 diff -uNr 09_hw_debug_JTAG/src/arch/aarch64/exception.rs 10_privilege_level/src/arch/aarch64/exception.rs
 --- 09_hw_debug_JTAG/src/arch/aarch64/exception.rs
 +++ 10_privilege_level/src/arch/aarch64/exception.rs
-@@ -0,0 +1,44 @@
+@@ -0,0 +1,48 @@
 +// SPDX-License-Identifier: MIT
 +//
 +// Copyright (c) 2018-2019 Andre Richter <andre.o.richter@gmail.com>
@@ -222,6 +222,10 @@ diff -uNr 09_hw_debug_JTAG/src/arch/aarch64/exception.rs 10_privilege_level/src/
 +
 +use cortex_a::regs::*;
 +
++//--------------------------------------------------------------------------------------------------
++// Arch-public
++//--------------------------------------------------------------------------------------------------
++
 +pub trait DaifField {
 +    fn daif_field() -> register::Field<u32, DAIF::Register>;
 +}
@@ -339,7 +343,7 @@ diff -uNr 09_hw_debug_JTAG/src/arch/aarch64.rs 10_privilege_level/src/arch/aarch
 +pub mod state {
 +    use cortex_a::regs::*;
 +
-+    /// The current privilege level.
++    /// The processing element's current privilege level.
 +    pub fn current_privilege_level() -> &'static str {
 +        let el = CurrentEL.read_as_enum(CurrentEL::EL);
 +        match el {

10_privilege_level/src/arch/aarch64.rs

@@ -108,7 +108,7 @@ pub fn wait_forever() -> ! {
 pub mod state {
     use cortex_a::regs::*;
 
-    /// The current privilege level.
+    /// The processing element's current privilege level.
     pub fn current_privilege_level() -> &'static str {
         let el = CurrentEL.read_as_enum(CurrentEL::EL);
         match el {

10_privilege_level/src/arch/aarch64/exception.rs

@@ -6,6 +6,10 @@
 
 use cortex_a::regs::*;
 
+//--------------------------------------------------------------------------------------------------
+// Arch-public
+//--------------------------------------------------------------------------------------------------
+
 pub trait DaifField {
     fn daif_field() -> register::Field<u32, DAIF::Register>;
 }

10_privilege_level/src/arch/aarch64/sync.rs

@@ -7,6 +7,10 @@
 use crate::interface;
 use core::cell::UnsafeCell;
 
+//--------------------------------------------------------------------------------------------------
+// Arch-public
+//--------------------------------------------------------------------------------------------------
+
 /// A pseudo-lock for teaching purposes.
 ///
 /// Used to introduce [interior mutability].
@@ -33,6 +37,10 @@ impl<T> NullLock<T> {
     }
 }
 
+//--------------------------------------------------------------------------------------------------
+// OS interface implementations
+//--------------------------------------------------------------------------------------------------
+
 impl<T> interface::sync::Mutex for &NullLock<T> {
     type Data = T;
 

10_privilege_level/src/arch/aarch64/time.rs

@@ -10,8 +10,16 @@ use cortex_a::regs::*;
 
 const NS_PER_S: u64 = 1_000_000_000;
 
+//--------------------------------------------------------------------------------------------------
+// Arch-public
+//--------------------------------------------------------------------------------------------------
+
 pub struct Timer;
 
+//--------------------------------------------------------------------------------------------------
+// OS interface implementations
+//--------------------------------------------------------------------------------------------------
+
 impl interface::time::Timer for Timer {
     fn resolution(&self) -> Duration {
         Duration::from_nanos(NS_PER_S / (CNTFRQ_EL0.get() as u64))

11_virtual_memory/README.md

@@ -262,10 +262,23 @@ make chainbot
 ## Diff to previous
 ```diff
 
+diff -uNr 10_privilege_level/Makefile 11_virtual_memory/Makefile
+--- 10_privilege_level/Makefile
++++ 11_virtual_memory/Makefile
+@@ -17,7 +17,7 @@
+ 	OPENOCD_ARG = -f /openocd/tcl/interface/ftdi/olimex-arm-usb-tiny-h.cfg -f /openocd/rpi3.cfg
+ 	JTAG_BOOT_IMAGE = jtag_boot_rpi3.img
+ 	LINKER_FILE = src/bsp/rpi/link.ld
+-	RUSTC_MISC_ARGS = -C target-cpu=cortex-a53
++	RUSTC_MISC_ARGS = -C target-cpu=cortex-a53 -C llvm-args=-ffixed-x18
+ else ifeq ($(BSP),rpi4)
+ 	TARGET = aarch64-unknown-none-softfloat
+ 	OUTPUT = kernel8.img
+
 diff -uNr 10_privilege_level/src/arch/aarch64/mmu.rs 11_virtual_memory/src/arch/aarch64/mmu.rs
 --- 10_privilege_level/src/arch/aarch64/mmu.rs
 +++ 11_virtual_memory/src/arch/aarch64/mmu.rs
-@@ -0,0 +1,309 @@
+@@ -0,0 +1,316 @@
 +// SPDX-License-Identifier: MIT
 +//
 +// Copyright (c) 2018-2019 Andre Richter <andre.o.richter@gmail.com>
@@ -275,7 +288,7 @@ diff -uNr 10_privilege_level/src/arch/aarch64/mmu.rs 11_virtual_memory/src/arch/
 +//! Static page tables, compiled on boot; Everything 64 KiB granule.
 +
 +use crate::{
-+    bsp,
++    bsp, interface,
 +    memory::{AccessPermissions, AttributeFields, MemAttributes},
 +};
 +use core::convert;
@@ -511,10 +524,7 @@ diff -uNr 10_privilege_level/src/arch/aarch64/mmu.rs 11_virtual_memory/src/arch/
 +            let virt_addr = (l2_nr << FIVETWELVE_MIB_SHIFT) + (l3_nr << SIXTYFOUR_KIB_SHIFT);
 +
 +            let (output_addr, attribute_fields) =
-+                match bsp::virt_mem_layout().get_virt_addr_properties(virt_addr) {
-+                    Err(string) => return Err(string),
-+                    Ok((a, b)) => (a, b),
-+                };
++                bsp::virt_mem_layout().get_virt_addr_properties(virt_addr)?;
 +
 +            *l3_entry = PageDescriptor::new(output_addr, attribute_fields).into();
 +        }
@@ -538,42 +548,52 @@ diff -uNr 10_privilege_level/src/arch/aarch64/mmu.rs 11_virtual_memory/src/arch/
 +    );
 +}
 +
-+/// Compile the page tables from the `BSP`-supplied `virt_mem_layout()`.
-+///
-+/// # Safety
-+///
-+/// - User must ensure that the hardware supports the paremeters being set here.
-+pub unsafe fn init() -> Result<(), &'static str> {
-+    // Fail early if translation granule is not supported. Both RPis support it, though.
-+    if !ID_AA64MMFR0_EL1.matches_all(ID_AA64MMFR0_EL1::TGran64::Supported) {
-+        return Err("64 KiB translation granule not supported");
-+    }
++//--------------------------------------------------------------------------------------------------
++// Arch-public
++//--------------------------------------------------------------------------------------------------
 +
-+    // Prepare the memory attribute indirection register.
-+    set_up_mair();
++pub struct MMU;
 +
-+    // Populate page tables.
-+    if let Err(string) = populate_pt_entries() {
-+        return Err(string);
-+    }
++//--------------------------------------------------------------------------------------------------
++// OS interface implementations
++//--------------------------------------------------------------------------------------------------
 +
-+    // Set the "Translation Table Base Register".
-+    TTBR0_EL1.set_baddr(TABLES.lvl2.base_addr_u64());
++impl interface::mm::MMU for MMU {
++    /// Compile the page tables from the `BSP`-supplied `virt_mem_layout()`.
++    ///
++    /// # Safety
++    ///
++    /// - User must ensure that the hardware supports the paremeters being set here.
++    unsafe fn init(&self) -> Result<(), &'static str> {
++        // Fail early if translation granule is not supported. Both RPis support it, though.
++        if !ID_AA64MMFR0_EL1.matches_all(ID_AA64MMFR0_EL1::TGran64::Supported) {
++            return Err("64 KiB translation granule not supported");
++        }
 +
-+    configure_translation_control();
++        // Prepare the memory attribute indirection register.
++        set_up_mair();
 +
-+    // Switch the MMU on.
-+    //
-+    // First, force all previous changes to be seen before the MMU is enabled.
-+    barrier::isb(barrier::SY);
++        // Populate page tables.
++        populate_pt_entries()?;
 +
-+    // Enable the MMU and turn on data and instruction caching.
-+    SCTLR_EL1.modify(SCTLR_EL1::M::Enable + SCTLR_EL1::C::Cacheable + SCTLR_EL1::I::Cacheable);
++        // Set the "Translation Table Base Register".
++        TTBR0_EL1.set_baddr(TABLES.lvl2.base_addr_u64());
 +
-+    // Force MMU init to complete before next instruction
-+    barrier::isb(barrier::SY);
++        configure_translation_control();
 +
-+    Ok(())
++        // Switch the MMU on.
++        //
++        // First, force all previous changes to be seen before the MMU is enabled.
++        barrier::isb(barrier::SY);
++
++        // Enable the MMU and turn on data and instruction caching.
++        SCTLR_EL1.modify(SCTLR_EL1::M::Enable + SCTLR_EL1::C::Cacheable + SCTLR_EL1::I::Cacheable);
++
++        // Force MMU init to complete before next instruction
++        barrier::isb(barrier::SY);
++
++        Ok(())
++    }
 +}
 
 diff -uNr 10_privilege_level/src/arch/aarch64.rs 11_virtual_memory/src/arch/aarch64.rs
@@ -583,10 +603,27 @@ diff -uNr 10_privilege_level/src/arch/aarch64.rs 11_virtual_memory/src/arch/aarc
  //! AArch64.
 
  mod exception;
-+pub mod mmu;
++mod mmu;
  pub mod sync;
  mod time;
 
+@@ -77,6 +78,7 @@
+ //--------------------------------------------------------------------------------------------------
+
+ static TIMER: time::Timer = time::Timer;
++static MMU: mmu::MMU = mmu::MMU;
+
+ //--------------------------------------------------------------------------------------------------
+ // Implementation of the kernel's architecture abstraction code
+@@ -136,3 +138,8 @@
+         println!("      FIQ:    {}", to_mask_str(exception::is_masked::<FIQ>()));
+     }
+ }
++
++/// Return a reference to an `interface::mm::MMU` implementation.
++pub fn mmu() -> &'static impl interface::mm::MMU {
++    &MMU
++}
 
 diff -uNr 10_privilege_level/src/bsp/rpi/link.ld 11_virtual_memory/src/bsp/rpi/link.ld
 --- 10_privilege_level/src/bsp/rpi/link.ld
@@ -637,7 +674,7 @@ diff -uNr 10_privilege_level/src/bsp/rpi/memory_map.rs 11_virtual_memory/src/bsp
 diff -uNr 10_privilege_level/src/bsp/rpi/virt_mem_layout.rs 11_virtual_memory/src/bsp/rpi/virt_mem_layout.rs
 --- 10_privilege_level/src/bsp/rpi/virt_mem_layout.rs
 +++ 11_virtual_memory/src/bsp/rpi/virt_mem_layout.rs
-@@ -0,0 +1,78 @@
+@@ -0,0 +1,82 @@
 +// SPDX-License-Identifier: MIT
 +//
 +// Copyright (c) 2018-2019 Andre Richter <andre.o.richter@gmail.com>
@@ -651,6 +688,10 @@ diff -uNr 10_privilege_level/src/bsp/rpi/virt_mem_layout.rs 11_virtual_memory/sr
 +use crate::memory::*;
 +use core::ops::RangeInclusive;
 +
++//--------------------------------------------------------------------------------------------------
++// BSP-public
++//--------------------------------------------------------------------------------------------------
++
 +pub const NUM_MEM_RANGES: usize = 3;
 +
 +pub static LAYOUT: KernelVirtualLayout<{ NUM_MEM_RANGES }> = KernelVirtualLayout::new(
@@ -760,6 +801,22 @@ diff -uNr 10_privilege_level/src/bsp.rs 11_virtual_memory/src/bsp.rs
  #[cfg(any(feature = "bsp_rpi3", feature = "bsp_rpi4"))]
  mod rpi;
 
+diff -uNr 10_privilege_level/src/interface.rs 11_virtual_memory/src/interface.rs
+--- 10_privilege_level/src/interface.rs
++++ 11_virtual_memory/src/interface.rs
+@@ -127,3 +127,11 @@
+         fn spin_for(&self, duration: Duration);
+     }
+ }
++
++/// Memory Management interfaces.
++pub mod mm {
++    pub trait MMU {
++        /// Called by the kernel early during init.
++        unsafe fn init(&self) -> Result<(), &'static str>;
++    }
++}
+
 diff -uNr 10_privilege_level/src/main.rs 11_virtual_memory/src/main.rs
 --- 10_privilege_level/src/main.rs
 +++ 11_virtual_memory/src/main.rs
@@ -780,7 +837,7 @@ diff -uNr 10_privilege_level/src/main.rs 11_virtual_memory/src/main.rs
  mod panic_wait;
  mod print;
 
-@@ -46,8 +49,16 @@
+@@ -46,8 +49,18 @@
  /// # Safety
  ///
  /// - Only a single core must be active and running this function.
@@ -791,14 +848,16 @@ diff -uNr 10_privilege_level/src/main.rs 11_virtual_memory/src/main.rs
 +///         drivers (which currently employ NullLocks instead of spinlocks), will fail to work on
 +///         the RPi SoCs.
  unsafe fn kernel_init() -> ! {
-+    if let Err(string) = arch::mmu::init() {
++    use interface::mm::MMU;
++
++    if let Err(string) = arch::mmu().init() {
 +        panic!("MMU: {}", string);
 +    }
 +
      for i in bsp::device_drivers().iter() {
          if let Err(()) = i.init() {
              panic!("Error loading driver: {}", i.compatible())
-@@ -67,6 +78,9 @@
+@@ -67,6 +80,9 @@
 
      println!("Booting on: {}", bsp::board_name());
 
@@ -808,7 +867,7 @@ diff -uNr 10_privilege_level/src/main.rs 11_virtual_memory/src/main.rs
      println!(
          "Current privilege level: {}",
          arch::state::current_privilege_level()
-@@ -87,6 +101,13 @@
+@@ -87,6 +103,13 @@
      println!("Timer test, spinning for 1 second");
      arch::timer().spin_for(Duration::from_secs(1));
 

11_virtual_memory/src/arch/aarch64.rs

@@ -5,7 +5,7 @@
 //! AArch64.
 
 mod exception;
-pub mod mmu;
+mod mmu;
 pub mod sync;
 mod time;
 
@@ -78,6 +78,7 @@ unsafe fn el2_to_el1_transition() -> ! {
 //--------------------------------------------------------------------------------------------------
 
 static TIMER: time::Timer = time::Timer;
+static MMU: mmu::MMU = mmu::MMU;
 
 //--------------------------------------------------------------------------------------------------
 // Implementation of the kernel's architecture abstraction code
@@ -109,7 +110,7 @@ pub fn wait_forever() -> ! {
 pub mod state {
     use cortex_a::regs::*;
 
-    /// The current privilege level.
+    /// The processing element's current privilege level.
     pub fn current_privilege_level() -> &'static str {
         let el = CurrentEL.read_as_enum(CurrentEL::EL);
         match el {
@@ -137,3 +138,8 @@ pub mod state {
         println!("      FIQ:    {}", to_mask_str(exception::is_masked::<FIQ>()));
     }
 }
+
+/// Return a reference to an `interface::mm::MMU` implementation.
+pub fn mmu() -> &'static impl interface::mm::MMU {
+    &MMU
+}

11_virtual_memory/src/arch/aarch64/exception.rs

@@ -6,6 +6,10 @@
 
 use cortex_a::regs::*;
 
+//--------------------------------------------------------------------------------------------------
+// Arch-public
+//--------------------------------------------------------------------------------------------------
+
 pub trait DaifField {
     fn daif_field() -> register::Field<u32, DAIF::Register>;
 }

11_virtual_memory/src/arch/aarch64/mmu.rs

@@ -7,7 +7,7 @@
 //! Static page tables, compiled on boot; Everything 64 KiB granule.
 
 use crate::{
-    bsp,
+    bsp, interface,
     memory::{AccessPermissions, AttributeFields, MemAttributes},
 };
 use core::convert;
@@ -243,10 +243,7 @@ unsafe fn populate_pt_entries() -> Result<(), &'static str> {
             let virt_addr = (l2_nr << FIVETWELVE_MIB_SHIFT) + (l3_nr << SIXTYFOUR_KIB_SHIFT);
 
             let (output_addr, attribute_fields) =
-                match bsp::virt_mem_layout().get_virt_addr_properties(virt_addr) {
-                    Err(string) => return Err(string),
-                    Ok((a, b)) => (a, b),
-                };
+                bsp::virt_mem_layout().get_virt_addr_properties(virt_addr)?;
 
             *l3_entry = PageDescriptor::new(output_addr, attribute_fields).into();
         }
@@ -270,40 +267,50 @@ fn configure_translation_control() {
     );
 }
 
-/// Compile the page tables from the `BSP`-supplied `virt_mem_layout()`.
-///
-/// # Safety
-///
-/// - User must ensure that the hardware supports the paremeters being set here.
-pub unsafe fn init() -> Result<(), &'static str> {
-    // Fail early if translation granule is not supported. Both RPis support it, though.
-    if !ID_AA64MMFR0_EL1.matches_all(ID_AA64MMFR0_EL1::TGran64::Supported) {
-        return Err("64 KiB translation granule not supported");
-    }
+//--------------------------------------------------------------------------------------------------
+// Arch-public
+//--------------------------------------------------------------------------------------------------
+
+pub struct MMU;
+
+//--------------------------------------------------------------------------------------------------
+// OS interface implementations
+//--------------------------------------------------------------------------------------------------
+
+impl interface::mm::MMU for MMU {
+    /// Compile the page tables from the `BSP`-supplied `virt_mem_layout()`.
+    ///
+    /// # Safety
+    ///
+    /// - User must ensure that the hardware supports the paremeters being set here.
+    unsafe fn init(&self) -> Result<(), &'static str> {
+        // Fail early if translation granule is not supported. Both RPis support it, though.
+        if !ID_AA64MMFR0_EL1.matches_all(ID_AA64MMFR0_EL1::TGran64::Supported) {
+            return Err("64 KiB translation granule not supported");
+        }
 
-    // Prepare the memory attribute indirection register.
-    set_up_mair();
+        // Prepare the memory attribute indirection register.
+        set_up_mair();
 
-    // Populate page tables.
-    if let Err(string) = populate_pt_entries() {
-        return Err(string);
-    }
+        // Populate page tables.
+        populate_pt_entries()?;
 
-    // Set the "Translation Table Base Register".
-    TTBR0_EL1.set_baddr(TABLES.lvl2.base_addr_u64());
+        // Set the "Translation Table Base Register".
+        TTBR0_EL1.set_baddr(TABLES.lvl2.base_addr_u64());
 
-    configure_translation_control();
+        configure_translation_control();
 
-    // Switch the MMU on.
-    //
-    // First, force all previous changes to be seen before the MMU is enabled.
-    barrier::isb(barrier::SY);
+        // Switch the MMU on.
+        //
+        // First, force all previous changes to be seen before the MMU is enabled.
+        barrier::isb(barrier::SY);
 
-    // Enable the MMU and turn on data and instruction caching.
-    SCTLR_EL1.modify(SCTLR_EL1::M::Enable + SCTLR_EL1::C::Cacheable + SCTLR_EL1::I::Cacheable);
+        // Enable the MMU and turn on data and instruction caching.
+        SCTLR_EL1.modify(SCTLR_EL1::M::Enable + SCTLR_EL1::C::Cacheable + SCTLR_EL1::I::Cacheable);
 
-    // Force MMU init to complete before next instruction
-    barrier::isb(barrier::SY);
+        // Force MMU init to complete before next instruction
+        barrier::isb(barrier::SY);
 
-    Ok(())
+        Ok(())
+    }
 }

11_virtual_memory/src/arch/aarch64/sync.rs

@@ -7,6 +7,10 @@
 use crate::interface;
 use core::cell::UnsafeCell;
 
+//--------------------------------------------------------------------------------------------------
+// Arch-public
+//--------------------------------------------------------------------------------------------------
+
 /// A pseudo-lock for teaching purposes.
 ///
 /// Used to introduce [interior mutability].
@@ -33,6 +37,10 @@ impl<T> NullLock<T> {
     }
 }
 
+//--------------------------------------------------------------------------------------------------
+// OS interface implementations
+//--------------------------------------------------------------------------------------------------
+
 impl<T> interface::sync::Mutex for &NullLock<T> {
     type Data = T;
 

11_virtual_memory/src/arch/aarch64/time.rs

@@ -10,8 +10,16 @@ use cortex_a::regs::*;
 
 const NS_PER_S: u64 = 1_000_000_000;
 
+//--------------------------------------------------------------------------------------------------
+// Arch-public
+//--------------------------------------------------------------------------------------------------
+
 pub struct Timer;
 
+//--------------------------------------------------------------------------------------------------
+// OS interface implementations
+//--------------------------------------------------------------------------------------------------
+
 impl interface::time::Timer for Timer {
     fn resolution(&self) -> Duration {
         Duration::from_nanos(NS_PER_S / (CNTFRQ_EL0.get() as u64))

11_virtual_memory/src/bsp/rpi/virt_mem_layout.rs

@@ -11,6 +11,10 @@ use super::memory_map;
 use crate::memory::*;
 use core::ops::RangeInclusive;
 
+//--------------------------------------------------------------------------------------------------
+// BSP-public
+//--------------------------------------------------------------------------------------------------
+
 pub const NUM_MEM_RANGES: usize = 3;
 
 pub static LAYOUT: KernelVirtualLayout<{ NUM_MEM_RANGES }> = KernelVirtualLayout::new(

11_virtual_memory/src/interface.rs

@@ -127,3 +127,11 @@ pub mod time {
         fn spin_for(&self, duration: Duration);
     }
 }
+
+/// Memory Management interfaces.
+pub mod mm {
+    pub trait MMU {
+        /// Called by the kernel early during init.
+        unsafe fn init(&self) -> Result<(), &'static str>;
+    }
+}

11_virtual_memory/src/main.rs

@@ -55,7 +55,9 @@ mod print;
 ///         drivers (which currently employ NullLocks instead of spinlocks), will fail to work on
 ///         the RPi SoCs.
 unsafe fn kernel_init() -> ! {
-    if let Err(string) = arch::mmu::init() {
+    use interface::mm::MMU;
+
+    if let Err(string) = arch::mmu().init() {
         panic!("MMU: {}", string);
     }