xous: wip commit

printf works now, and we're getting the page table stuff set up.

Signed-off-by: Sean Cross <sean@xobs.io>

.vscode/settings.json

@@ -0,0 +1,23 @@
+{
+    "cSpell.words": [
+        "TXFULL",
+        "Uart",
+        "concat",
+        "ebss",
+        "edata",
+        "eheap",
+        "estack",
+        "etext",
+        "getc",
+        "mstatus",
+        "pagetable",
+        "putc",
+        "satp",
+        "sbss",
+        "sdata",
+        "sheap",
+        "sidata",
+        "sstack",
+        "stext"
+    ]
+}

src/debug.rs

@@ -0,0 +1,89 @@
+use core::fmt::{Error, Write};
+
+#[macro_export]
+macro_rules! print
+{
+	($($args:tt)+) => ({
+			use core::fmt::Write;
+			let _ = write!(crate::debug::DEFAULT_UART, $($args)+);
+	});
+}
+#[macro_export]
+macro_rules! println
+{
+	() => ({
+		print!("\r\n")
+	});
+	($fmt:expr) => ({
+		print!(concat!($fmt, "\r\n"))
+	});
+	($fmt:expr, $($args:tt)+) => ({
+		print!(concat!($fmt, "\r\n"), $($args)+)
+	});
+}
+
+pub struct Uart {
+    base: *mut usize,
+}
+
+pub const DEFAULT_UART: Uart = Uart {
+    base: 0xE000_1800 as *mut usize,
+};
+
+impl Uart {
+    // pub fn new(base_addr: usize) -> Uart {
+    //     Uart {
+    //         base: base_addr as *mut usize,
+    //     }
+    // }
+
+    pub fn enable_rx(self) {
+        unsafe {
+            self.base
+                .add(5)
+                .write_volatile(self.base.add(5).read_volatile() | 2)
+        };
+    }
+
+    pub fn putc(&self, c: u8) {
+        unsafe {
+            // Wait until TXFULL is `0`
+            while self.base.add(1).read_volatile() != 0 {
+                ()
+            }
+            self.base.add(0).write_volatile(c as usize)
+        };
+    }
+
+    pub fn getc(&self) -> Option<u8> {
+        unsafe {
+            // If EV_PENDING_RX is 1, return the pending character.
+            // Otherwise, return None.
+            match self.base.add(4).read_volatile() & 2 {
+                0 => None,
+                ack => {
+                    let c = Some(self.base.add(0).read_volatile() as u8);
+                    self.base.add(4).write_volatile(ack);
+                    c
+                }
+            }
+        }
+    }
+}
+
+pub fn irq(irq_number: usize) {
+    println!(
+        "Interrupt {}: Key pressed: {}",
+        irq_number,
+        DEFAULT_UART.getc().unwrap() as char
+    );
+}
+
+impl Write for Uart {
+    fn write_str(&mut self, s: &str) -> Result<(), Error> {
+        for c in s.bytes() {
+            self.putc(c);
+        }
+        Ok(())
+    }
+}

src/main.rs

@@ -2,6 +2,8 @@
 #![no_main]
 
 extern crate vexriscv;
+
+mod debug;
 mod definitions;
 mod irq;
 mod macros;
@@ -12,22 +14,16 @@ mod syscalls;
 pub use irq::sys_interrupt_claim;
 
 use core::panic::PanicInfo;
-use xous_kernel_riscv_rt::xous_kernel_entry;
-use vexriscv::register::{mcause, mstatus, mie, vmim, vmip};
 use mem::MemoryManager;
 use processtable::ProcessTable;
+use vexriscv::register::{mcause, mie, mstatus, vmim, vmip};
+use xous_kernel_riscv_rt::xous_kernel_entry;
 
 #[panic_handler]
 fn handle_panic(_arg: &PanicInfo) -> ! {
     loop {}
 }
 
-fn print_str(uart: *mut usize, s: &str) {
-    for c in s.bytes() {
-        unsafe { uart.write_volatile(c as usize) };
-    }
-}
-
 #[xous_kernel_entry]
 fn xous_main() -> ! {
     unsafe {
@@ -37,30 +33,21 @@ fn xous_main() -> ! {
         mie::set_mext();
         mstatus::set_mie(); // Enable CPU interrupts
     }
-    let mut mm = MemoryManager::new();
-    let mut pt = ProcessTable::new(&mut mm);
 
-    sys_interrupt_claim(2, |_| {
-        let uart_ptr = 0xE000_1800 as *mut usize;
-        print_str(uart_ptr, "hello, world!\r\n");
-        // Acknowledge the IRQ
-        unsafe {
-            uart_ptr.add(0).read_volatile();
+    let uart = debug::DEFAULT_UART;
+
+    // Enable "RX_EMPTY" interrupt
+    uart.enable_rx();
 
-            // Acknowledge the event
-            uart_ptr.add(4).write_volatile(3);
-        };
-    })
-    .unwrap();
+    println!("Starting up...");
+    sys_interrupt_claim(2, debug::irq).unwrap();
+
+    let mut mm = MemoryManager::new();
+    let mut _pt = ProcessTable::new(&mut mm);
 
-    // Enable interrupts
-    let uart_ptr = 0xE000_1800 as *mut usize;
-    unsafe { uart_ptr.add(4).write_volatile(3) };
-    unsafe { uart_ptr.add(5).write_volatile(3) };
-    print_str(uart_ptr, "greetings!\r\n");
 
     loop {
-        unsafe { vexriscv::asm::wfi() };
+        // unsafe { vexriscv::asm::wfi() };
     }
 }
 
@@ -69,7 +56,10 @@ pub fn trap_handler() {
     let mc = mcause::read();
     let irqs_pending = vmip::read();
 
-    if mc.is_exception() {}
+    if mc.is_exception() {
+        unsafe { vexriscv::asm::ebreak() };
+        loop {}
+    }
 
     if irqs_pending != 0 {
         irq::handle(irqs_pending);

src/mem.rs

@@ -1,4 +1,5 @@
-use crate::definitions::{XousError, XousPid, MemoryAddress};
+use crate::definitions::{MemoryAddress, XousError, XousPid};
+use crate::{print, println};
 use core::num::NonZeroUsize;
 use vexriscv::register::mstatus;
 
@@ -21,6 +22,7 @@ const FLASH_PAGE_COUNT: usize = FLASH_SIZE / PAGE_SIZE;
 const RAM_PAGE_COUNT: usize = RAM_SIZE / PAGE_SIZE;
 const IO_PAGE_COUNT: usize = IO_SIZE;
 const LCD_PAGE_COUNT: usize = LCD_SIZE / PAGE_SIZE;
+
 pub struct MemoryManager {
     flash: [XousPid; FLASH_PAGE_COUNT],
     ram: [XousPid; RAM_PAGE_COUNT],
@@ -28,6 +30,43 @@ pub struct MemoryManager {
     lcd: [XousPid; LCD_PAGE_COUNT],
 }
 
+impl core::fmt::Debug for MemoryManager {
+    fn fmt(&self, fmt: &mut core::fmt::Formatter) -> core::result::Result<(), core::fmt::Error> {
+        writeln!(fmt, "MemoryManager: ")?;
+        writeln!(
+            fmt,
+            "    flash: {:08x} .. {:08x} ({})",
+            FLASH_START,
+            FLASH_END,
+            self.flash.len()
+        )?;
+        writeln!(
+            fmt,
+            "    ram:   {:08x} .. {:08x} ({})",
+            RAM_START,
+            RAM_END,
+            self.ram.len()
+        )?;
+        writeln!(
+            fmt,
+            "    io:    {:08x} .. {:08x} ({})",
+            IO_START,
+            IO_END,
+            self.io.len()
+        )?;
+        writeln!(
+            fmt,
+            "    lcd:   {:08x} .. {:08x} ({})",
+            LCD_START,
+            LCD_END,
+            self.lcd.len()
+        )?;
+        Ok(())
+    }
+}
+
+/// A single RISC-V page table entry.  In order to resolve an address,
+/// we need two entries: the top level, followed by the lower level.
 struct PageTable {
     entries: [usize; 1024],
 }
@@ -59,6 +98,14 @@ extern "C" {
 
 use core::mem::transmute;
 
+/// Enable transmuting from pointers-to-addresses to addresses.
+/// This is required because the linker creates variables
+/// such as _stext that are located at specific offsets -- such
+/// as the start of the text section -- and their address is
+/// the actual piece of data we want.
+/// Rust really doesn't like going from addresses to values, so
+/// we transmute from one to the other in order to construct a
+/// range that we can loop through.
 macro_rules! mem_range {
     ( $s:expr, $e:expr ) => {{
         let start = unsafe { transmute::<&usize, usize>(&$s) };
@@ -67,7 +114,7 @@ macro_rules! mem_range {
     }}
 }
 
-/// Initialzie the memory map.
+/// Initialize the memory map.
 /// This will go through memory and map anything that the kernel is
 /// using to process 1, then allocate a pagetable for this process
 /// and place it at the usual offset.  The MMU will not be enabled yet,
@@ -80,54 +127,62 @@ impl MemoryManager {
             io: [0; IO_PAGE_COUNT],
             lcd: [0; LCD_PAGE_COUNT],
         };
+        println!("Created Memory Manager: {:?}", mm);
+
+        // Claim existing pages for PID 1, in preparation for turning on
+        // the MMU
+        unsafe { mstatus::clear_mie() };
+
+        let ranges = [
+            mem_range!(&_sbss, &_ebss),
+            mem_range!(&_sdata, &_edata),
+            mem_range!(&_estack, &_sstack), // NOTE: Stack is reversed
+            mem_range!(&_stext, &_etext),
+        ];
+        for range in &ranges {
+            for region in range.clone() {
+                mm.claim_page(region & !0xfff, 1)
+                    .expect("Unable to claim region for PID 1");
+            }
+        }
+
+        unsafe { mstatus::set_mie() };
 
         mm
     }
 
     /// Allocate a single page to the given process.
+    /// Ensures the page is zeroed out prior to handing it over to
+    /// the specified process.
     pub fn alloc_page(&mut self, pid: XousPid) -> Result<MemoryAddress, XousError> {
         // Go through all RAM pages looking for a free page.
         // Optimization: start from the previous address.
+        println!("Allocating page for PID {}", pid);
         for index in 0..RAM_PAGE_COUNT {
+            println!("    Checking {:08x}...", index * PAGE_SIZE + RAM_START);
             if self.ram[index] == 0 {
                 self.ram[index] = pid;
                 let page_addr = (index * PAGE_SIZE + RAM_START) as *mut u32;
                 // Zero-out the page
                 unsafe {
-                    for i in 0..PAGE_SIZE/4 {
+                    for i in 0..PAGE_SIZE / 4 {
                         *page_addr.add(i) = 0;
                     }
                 }
                 let new_page = unsafe { transmute::<*mut u32, usize>(page_addr) };
+                println!("    Page {:08x} is free", new_page);
                 return Ok(NonZeroUsize::new(new_page).unwrap());
             }
         }
         Err(XousError::OutOfMemory)
     }
 
-    /// Create an identity mapping, copying the kernel to itself
-    pub fn create_identity(&mut self, satp: MemoryAddress, pid: XousPid) -> Result<(), XousError> {
-        let pt = unsafe { transmute::<MemoryAddress, &mut PageTable>(satp) };
+    // /// Create an identity mapping, copying the kernel to itself
+    // pub fn create_identity(&mut self, pid: XousPid) -> Result<(), XousError> {
+    //     let pt = unsafe { transmute::<MemoryAddress, &mut PageTable>(satp) };
 
-        unsafe { mstatus::clear_mie() };
-
-        let ranges = [
-            mem_range!(&_sbss, &_ebss),
-            mem_range!(&_sdata, &_edata),
-            mem_range!(&_estack, &_sstack), // NOTE: Stack is reversed
-            mem_range!(&_stext, &_etext),
-        ];
-        for range in &ranges {
-            for region in range.clone() {
-                self.map_page(pt, pid)?;
-                self.claim_page(region & !0xfff, 1)?;
-            }
-        }
-
-        unsafe { mstatus::set_mie() };
-
-        Err(XousError::OutOfMemory)
-    }
+    //     Err(XousError::OutOfMemory)
+    // }
 
     fn map_page(&mut self, satp: &mut PageTable, pid: XousPid) -> Result<(), XousError> {
         Err(XousError::OutOfMemory)
@@ -153,14 +208,11 @@ impl MemoryManager {
         }
 
         match addr {
-            FLASH_START..=FLASH_END => {
-                claim_page_inner(&mut self.flash, addr - FLASH_START, pid)
-            }
+            FLASH_START..=FLASH_END => claim_page_inner(&mut self.flash, addr - FLASH_START, pid),
             RAM_START..=RAM_END => claim_page_inner(&mut self.ram, addr - RAM_START, pid),
             IO_START..=IO_END => claim_page_inner(&mut self.io, addr - IO_START, pid),
             LCD_START..=LCD_END => claim_page_inner(&mut self.lcd, addr - LCD_START, pid),
             _ => Err(XousError::BadAddress),
         }
     }
-
 }

src/processtable.rs

@@ -1,6 +1,6 @@
 use crate::definitions::{XousError, XousPid, MemoryAddress};
 use crate::mem::MemoryManager;
-use crate::filled_array;
+use crate::{filled_array, println, print};
 
 const MAX_PROCESS_COUNT: usize = 256;
 
@@ -8,6 +8,12 @@ struct Process {
     satp: Option<MemoryAddress>,
 }
 
+impl core::fmt::Debug for Process {
+    fn fmt(&self, fmt: &mut core::fmt::Formatter) -> core::result::Result<(), core::fmt::Error> {
+        write!(fmt, "Process (satp: 0x{:08x})", match self.satp { Some(s) => s.get(), None => 0 })
+    }
+}
+
 pub struct ProcessTable {
     processes: [Process; MAX_PROCESS_COUNT],
 }
@@ -19,8 +25,9 @@ impl ProcessTable {
         };
 
         // Allocate a root page table for PID 1
+        // mm.create_identity(1).expect("Unable to create identity mapping");
         pt.processes[1].satp = Some(mm.alloc_page(1).unwrap());
-        mm.create_identity(pt.processes[1].satp.unwrap(), 1).expect("Unable to create identity mapping");
+        println!("PID 1: {:?}", pt.processes[1]);
         pt
     }
 }