From f778d0ebb7a5b9095958cce741bf0fdcccc5641c Mon Sep 17 00:00:00 2001
From: Allen Aboytes <aaboytes@ucsc.edu>
Date: Fri, 19 Jan 2024 10:32:18 -0800
Subject: [PATCH] Handle RX interrupts from the UART

---
 src/kernel/src/arch/aarch64/interrupt.rs  |  5 ++++
 src/kernel/src/machine/arm/common/uart.rs | 13 ++++++++++
 src/kernel/src/machine/arm/virt/mod.rs    |  3 ++-
 src/kernel/src/machine/arm/virt/serial.rs | 31 +++++++++++++++++++++++
 4 files changed, 51 insertions(+), 1 deletion(-)

diff --git a/src/kernel/src/arch/aarch64/interrupt.rs b/src/kernel/src/arch/aarch64/interrupt.rs
index f0ba63ea..97e3c98d 100644
--- a/src/kernel/src/arch/aarch64/interrupt.rs
+++ b/src/kernel/src/arch/aarch64/interrupt.rs
@@ -16,6 +16,7 @@ use crate::{
     processor::current_processor,
 };
 use crate::machine::interrupt::INTERRUPT_CONTROLLER;
+use crate::machine::serial::{SERIAL_INT_ID, serial_interrupt_handler};
 
 use super::exception::{
     ExceptionContext, exception_handler, save_stack_pointer, restore_stack_pointer,
@@ -138,6 +139,10 @@ pub(super) fn irq_exception_handler(_ctx: &mut ExceptionContext) {
             // call timer interrupt handler
             cntp_interrupt_handler();
         },
+        _ if irq_number == *SERIAL_INT_ID => {
+            // call the serial interrupt handler
+            serial_interrupt_handler();
+        },
         _ => panic!("unknown irq number! {}", irq_number)
     }
     // signal the GIC that we have serviced the IRQ
diff --git a/src/kernel/src/machine/arm/common/uart.rs b/src/kernel/src/machine/arm/common/uart.rs
index a7970e58..c9c28f79 100644
--- a/src/kernel/src/machine/arm/common/uart.rs
+++ b/src/kernel/src/machine/arm/common/uart.rs
@@ -19,6 +19,7 @@ enum Registers {
     UARTLCR_H = 0x02C,
     UARTCR = 0x030,
     UARTIMSC = 0x038,
+    UARTICR = 0x044,
     UARTDMACR = 0x048,
 }
 
@@ -176,6 +177,18 @@ impl PL011 {
         }
     }
 
+    pub fn clear_rx_interrupt(&self) {
+        // The UARTICR Register is the interrupt clear register and is write-only. 
+        // On a write of 1, the corresponding interrupt is cleared. 
+        // A write of 0 has no effect. Table 3-17 lists the register bit assignments.
+        //
+        // We must write to Receive interrupt clear (RXIC) which is bit 4. This
+        // Clears the UARTRXINTR interrupt.
+        unsafe {
+            self.write_reg(Registers::UARTICR, (0b1 << 4) as u32);
+        }
+    }
+
     /// Write a value to a single register. Registers are 32-bits wide.
     unsafe fn write_reg(&self, register: Registers, value: u32) {
         let reg = (self.base + register as usize) as *mut u32;
diff --git a/src/kernel/src/machine/arm/virt/mod.rs b/src/kernel/src/machine/arm/virt/mod.rs
index a2fe57c9..8f0a4777 100644
--- a/src/kernel/src/machine/arm/virt/mod.rs
+++ b/src/kernel/src/machine/arm/virt/mod.rs
@@ -5,5 +5,6 @@ pub mod processor;
 pub mod serial;
 
 pub fn machine_post_init() {
-    // TODO: initialize uart with interrupts
+    // initialize uart with interrupts
+    serial::SERIAL.late_init();
 }
\ No newline at end of file
diff --git a/src/kernel/src/machine/arm/virt/serial.rs b/src/kernel/src/machine/arm/virt/serial.rs
index c76a253e..00c57eb4 100644
--- a/src/kernel/src/machine/arm/virt/serial.rs
+++ b/src/kernel/src/machine/arm/virt/serial.rs
@@ -7,6 +7,7 @@ use crate::memory::{PhysAddr, pagetables::{
     ContiguousProvider, MappingCursor, MappingSettings, Mapper,
     MappingFlags,
 }};
+use crate::interrupt::{Destination, TriggerMode};
 use crate::arch::memory::mmio::MMIO_ALLOCATOR;
 
 lazy_static! {
@@ -47,6 +48,12 @@ lazy_static! {
         serial_port.early_init(clock_freq as u32);
         serial_port
     };
+
+    pub static ref SERIAL_INT_ID: u32 = {
+        let int_num = crate::machine::info::get_uart_interrupt_num()
+            .expect("failed to decode UART interrupt number");
+        int_num
+    };
 }
 
 impl PL011 {
@@ -64,6 +71,22 @@ impl PL011 {
             self.init(clock_freq, BAUD);
         }
     }
+
+    /// intitialize the UART driver after the system has enabled interrupts
+    pub fn late_init(&self) {
+        // enable the rx side to use interrupts
+        unsafe {
+            self.enable_rx_interrupt();
+        }
+
+        crate::arch::set_interrupt(
+            *SERIAL_INT_ID,
+            false,
+            TriggerMode::Edge,
+            crate::interrupt::PinPolarity::ActiveHigh,
+            Destination::Bsp,
+        );
+    }
 }
 
 pub fn write(data: &[u8], _flags: crate::log::KernelConsoleWriteFlags) {
@@ -80,3 +103,11 @@ pub fn write(data: &[u8], _flags: crate::log::KernelConsoleWriteFlags) {
         }
     }
 }
+
+pub fn serial_interrupt_handler() {
+    let byte = SERIAL.rx_byte();
+    if let Some(x) = byte {
+        crate::log::push_input_byte(x);
+    }
+    SERIAL.clear_rx_interrupt();
+}