From 92ac3931ec7c2ee7746d38499edd9179c943c5ac Mon Sep 17 00:00:00 2001
From: Richard Qin <richard.qin.x@gmail.com>
Date: Tue, 21 Apr 2026 23:20:56 +0800
Subject: feat: add initial implementation of PLIC and UART drivers

---
 na/drivers/plic.cc | 24 ++++++++++++++++++++++++
 na/drivers/uart.cc | 44 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 68 insertions(+)
 create mode 100644 na/drivers/plic.cc
 create mode 100644 na/drivers/uart.cc

diff --git a/na/drivers/plic.cc b/na/drivers/plic.cc
new file mode 100644
index 0000000..f640a2a
--- /dev/null
+++ b/na/drivers/plic.cc
@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* Copyright (C) 2026 Richard Qin */
+
+/*
+ * plic.cc — Platform-Level Interrupt Controller stub
+ */
+
+#include <lume/fdt.h>
+#include <lume/vmm.h>
+#include <arch/config.h>
+
+void plic_init() {
+    /* 
+     * In a fully implemented driver, we would discover the PLIC base 
+     * and size via FDT. For now, we map the default QEMU virt PLIC.
+     */
+    uint64 plic_pa = arch::kDefaultPlicPA;
+    /* QEMU virt PLIC is 0x4000000 in size */
+    vmm_map_kernel_mmio(plic_pa, 0x4000000);
+}
+
+void plic_init_ap() {
+    /* AP per-CPU init */
+}
diff --git a/na/drivers/uart.cc b/na/drivers/uart.cc
new file mode 100644
index 0000000..802e88d
--- /dev/null
+++ b/na/drivers/uart.cc
@@ -0,0 +1,44 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* Copyright (C) 2026 Richard Qin */
+
+/*
+ * uart.cc — 16550a UART driver (early console)
+ *
+ * Implements the early UART output mapping required by panic and kernel_main.
+ */
+
+#include <lume/console.h>
+#include <lume/fdt.h>
+#include <lume/vmm.h>
+#include <lume/addr.h>
+#include <arch/config.h>
+
+static uint64 g_uart_pa = arch::kDefaultUartPA;
+
+extern "C" void early_putc(char c) {
+    if (!g_uart_pa) return;
+    volatile auto* uart = reinterpret_cast<volatile uint8*>(pa_to_va(g_uart_pa));
+    *uart = static_cast<uint8>(c);
+}
+
+extern "C" void early_puts(const char* s) {
+    while (*s) early_putc(*s++);
+}
+
+void console_early_init(uint64 fdt_paddr) {
+    uint64 pa = 0;
+    FdtManager::early_scan_uart(fdt_paddr, &pa);
+    if (pa != 0) {
+        g_uart_pa = pa;
+    }
+}
+
+void console_init() {
+    /*
+     * Once vmm_init() activates the new page table, the 1GB identity map is dropped.
+     * The UART must be explicitly registered into the active page table.
+     */
+    if (g_uart_pa != 0) {
+        vmm_map_kernel_mmio(g_uart_pa, 0x1000);
+    }
+}
-- 
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