feat: implement MMU core functionality

* feat: Implement a basic MMU configuration

* feat: Enhance MMU by separating sections and configuring permissions

* feat: Update MMU configuration and memory allocation functions

* fix: Level 3 translation fault

* docs: add code documentation

* fix: linter

* feat: map translation tables to kernel space

* feat: move el1 stack to kernel VA space

* feat: use virtual memory for heap allocation

* docs: update Readme

src/pi3/mod.rs

@@ -1,2 +1,3 @@
 pub mod mailbox;
 pub mod power_management;
+pub mod timer;

src/pi3/power_management.rs

@@ -3,7 +3,7 @@ use core::ptr::{read_volatile, write_volatile};
 use crate::PERIPHERAL_BASE;
 
 /// Power Management Base
-static PM_BASE: u32 = PERIPHERAL_BASE + 0x10_0000;
+static PM_BASE: u32 = PERIPHERAL_BASE as u32 + 0x10_0000;
 static PM_RSTC: u32 = PM_BASE + 0x1c;
 static PM_WDOG: u32 = PM_BASE + 0x24;
 
@@ -23,5 +23,6 @@ pub fn reboot_system() {
             PM_PASSWORD | (pm_rstc_val & PM_RSTC_WRCFG_CLR) | PM_RSTC_WRCFG_FULL_RESET,
         );
     }
+    #[allow(clippy::empty_loop)]
     loop {}
 }

src/pi3/timer.rs

@@ -0,0 +1,61 @@
+use core::{hint::spin_loop, ptr::read_volatile};
+
+const TIMER_CLOCK_LO: u32 = 0x3F00_3004;
+const TIMER_CLOCK_HI: u32 = 0x3F00_3008;
+
+fn read_timer_32() -> u32 {
+    unsafe { read_volatile(TIMER_CLOCK_LO as *const u32) }
+}
+
+fn read_timer_64() -> u64 {
+    loop {
+        let clock_hi1 = unsafe { read_volatile(TIMER_CLOCK_HI as *const u32) };
+        let clock_lo = unsafe { read_volatile(TIMER_CLOCK_LO as *const u32) };
+        let clock_hi2 = unsafe { read_volatile(TIMER_CLOCK_HI as *const u32) };
+
+        // account for roll over during read
+        if clock_hi1 == clock_hi2 {
+            return ((clock_hi1 as u64) << 32) | clock_lo as u64;
+        }
+    }
+}
+
+/// Sleep for `us` microseconds
+pub fn sleep_us(us: u64) {
+    if us < u32::MAX as u64 {
+        sleep_us_u32(us as u32);
+    } else {
+        sleep_us_u64(us);
+    }
+}
+
+fn sleep_us_u32(us: u32) {
+    let start = read_timer_32();
+    while read_timer_32().wrapping_sub(start) < us {
+        spin_loop();
+    }
+}
+
+fn sleep_us_u64(us: u64) {
+    let start = read_timer_64();
+    while read_timer_64().wrapping_sub(start) < us {
+        spin_loop();
+    }
+}
+
+/// Sleep for `ms` milliseconds
+pub fn sleep_ms(ms: u64) {
+    sleep_us(ms * 1_000);
+}
+
+/// Sleep for `s` seconds
+pub fn sleep_s(s: u64) {
+    sleep_ms(s * 1_000);
+}
+
+/// Wait for `count` operations to pass
+pub fn delay_nops(count: u32) {
+    for _ in 0..count {
+        spin_loop()
+    }
+}