Basic documentation

README.md

@@ -3,3 +3,13 @@
 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/)
+
+## Features
+
+- Delay and sleep ✓
+- UART ✓
+- GPIOs ✓
+- GPIO Interrupts ✓
+- Frame Buffer
+- MMU
+- Basic Terminal over UART

src/main.rs

@@ -12,7 +12,7 @@ use nova::{
     peripherals::{
         gpio::{
             gpio_get_state, gpio_high, gpio_low, gpio_pull_up, set_falling_edge_detect,
-            set_gpio_state, GPIOState,
+            set_gpio_function, GPIOFunction,
         },
         uart::{print, uart_init},
     },
@@ -49,7 +49,7 @@ pub extern "C" fn main() -> ! {
     enable_uart();
 
     // Set ACT Led to Outout
-    let _ = set_gpio_state(21, GPIOState::Output);
+    let _ = set_gpio_function(21, GPIOFunction::Output);
 
     print_current_el_str();
 
@@ -72,7 +72,7 @@ pub extern "C" fn kernel_main() -> ! {
 
     // Set GPIO 26 to Input
     enable_irq_source(nova::irq_interrupt::IRQState::GpioInt0); //26 is on the first GPIO bank
-    let _ = set_gpio_state(26, GPIOState::Input);
+    let _ = set_gpio_function(26, GPIOFunction::Input);
     gpio_pull_up(26);
     set_falling_edge_detect(26, true);
 
@@ -112,8 +112,8 @@ pub fn get_current_el() -> u64 {
 fn enable_uart() {
     uart_init();
     // Set GPIO Pins to UART
-    let _ = set_gpio_state(14, GPIOState::Alternative0);
+    let _ = set_gpio_function(14, GPIOFunction::Alternative0);
-    let _ = set_gpio_state(15, GPIOState::Alternative0);
+    let _ = set_gpio_function(15, GPIOFunction::Alternative0);
 }
 
 fn print_current_el_str() {

src/peripherals/gpio.rs

@@ -1,6 +1,5 @@
 use core::ptr::{read_volatile, write_volatile};
 use core::result::Result;
-use core::result::Result::Err;
 use core::result::Result::Ok;
 
 use crate::timer::delay_nops;
@@ -15,7 +14,7 @@ const GPREN_BASE: u32 = 0x3F20_004C;
 const GPFEN_BASE: u32 = 0x3F20_0058;
 
 #[repr(u32)]
-pub enum GPIOState {
+pub enum GPIOFunction {
     Input = 0b000,
     Output = 0b001,
     Alternative0 = 0b100,
@@ -26,11 +25,8 @@ pub enum GPIOState {
     Alternative5 = 0b010,
 }
 
-pub fn set_gpio_state(gpio: u8, state: GPIOState) -> Result<(), &'static str> {
+/// Set the function of the GPIO pin
-    if gpio > 53 {
+pub fn set_gpio_function(gpio: u8, state: GPIOFunction) -> Result<(), &'static str> {
-        return Err("GPIO out of range");
-    }
-
     let register_index = gpio / 10;
     let register_offset = (gpio % 10) * 3;
     let register_addr = GPFSEL_BASE + (register_index as u32 * 4);
@@ -47,6 +43,9 @@ pub fn set_gpio_state(gpio: u8, state: GPIOState) -> Result<(), &'static str> {
     Ok(())
 }
 
+/// Set the GPIO to high
+///
+/// Should be used when GPIO function is set to `OUTPUT` via `set_gpio_function`
 pub fn gpio_high(gpio: u8) -> Result<(), &'static str> {
     unsafe {
         let register_index = gpio / 32;
@@ -58,6 +57,9 @@ pub fn gpio_high(gpio: u8) -> Result<(), &'static str> {
     Ok(())
 }
 
+/// Set the GPIO to low
+///
+/// Should be used when GPIO function is set to `OUTPUT` via `set_gpio_function`
 pub fn gpio_low(gpio: u8) -> Result<(), &'static str> {
     unsafe {
         let register_index = gpio / 32;
@@ -69,6 +71,7 @@ pub fn gpio_low(gpio: u8) -> Result<(), &'static str> {
     Ok(())
 }
 
+/// Read the current GPIO power state
 pub fn gpio_get_state(gpio: u8) -> u8 {
     unsafe {
         let register_index = gpio / 32;
@@ -80,10 +83,16 @@ pub fn gpio_get_state(gpio: u8) -> u8 {
     }
 }
 
+/// Pull GPIO up
+///
+/// Should be used when GPIO function is set to `INPUT` via `set_gpio_function`
 pub fn gpio_pull_up(gpio: u8) {
     gpio_pull_up_down(gpio, 0b10);
 }
 
+/// Pull GPIO down
+///
+/// Should be used when GPIO function is set to `INPUT` via `set_gpio_function`
 pub fn gpio_pull_down(gpio: u8) {
     gpio_pull_up_down(gpio, 0b01);
 }
@@ -115,20 +124,31 @@ fn gpio_pull_up_down(gpio: u8, val: u32) {
     }
 }
 
-pub fn read_falling_edge_detect(gpio: u8) -> u32 {
+/// Get the current status if falling edge detection is set
+pub fn read_falling_edge_detect(gpio: u8) -> bool {
     unsafe {
-        // Determine GPLEN Register
         let register_addr = GPFEN_BASE + 4 * (gpio as u32 / 32);
         let register_offset = gpio % 32;
 
         let current = read_volatile(register_addr as *const u32);
-        return (current >> register_offset) & 0b1;
+        ((current >> register_offset) & 0b1) != 0
     }
 }
 
+/// Get the current status if falling edge detection is set
+pub fn read_rising_edge_detect(gpio: u8) -> bool {
+    unsafe {
+        let register_addr = GPREN_BASE + 4 * (gpio as u32 / 32);
+        let register_offset = gpio % 32;
+
+        let current = read_volatile(register_addr as *const u32);
+        ((current >> register_offset) & 0b1) != 0
+    }
+}
+
+/// Enables falling edge detection
 pub fn set_falling_edge_detect(gpio: u8, enable: bool) {
     unsafe {
-        // Determine GPLEN Register
         let register_addr = GPFEN_BASE + 4 * (gpio as u32 / 32);
         let register_offset = gpio % 32;
 
@@ -144,9 +164,9 @@ pub fn set_falling_edge_detect(gpio: u8, enable: bool) {
     }
 }
 
+/// Enables rising edge detection
 pub fn set_rising_edge_detect(gpio: u8, enable: bool) {
     unsafe {
-        // Determine GPHEN Register
         let register_addr = GPREN_BASE + 4 * (gpio as u32 / 32);
         let register_offset = gpio % 32;