From 1f25cc23da58a7ab8a9800a0a431d2f1bc49abd0 Mon Sep 17 00:00:00 2001
From: FyloZ <fylozdev@gmail.com>
Date: Sat, 21 Feb 2026 22:00:38 -0500
Subject: [PATCH] Basic UART communications

---
 .idea/editor.xml                             |  2 +-
 .idea/inspectionProfiles/Project_Default.xml |  6 ++
 src/kernel/common.h                          | 11 +++
 src/kernel/kernel.c                          | 44 ++---------
 src/kernel/riscv64/common.c                  | 21 +++++
 src/kernel/riscv64/qemu/syscon.c             |  3 +
 src/kernel/riscv64/qemu/uart.c               | 81 ++++++++++++++++++++
 src/kernel/uart.c                            |  3 -
 src/kernel/uart.h                            | 34 ++++++++
 9 files changed, 162 insertions(+), 43 deletions(-)
 create mode 100644 .idea/inspectionProfiles/Project_Default.xml
 create mode 100644 src/kernel/common.h
 create mode 100644 src/kernel/riscv64/common.c
 create mode 100644 src/kernel/riscv64/qemu/uart.c
 delete mode 100644 src/kernel/uart.c
 create mode 100644 src/kernel/uart.h

diff --git a/.idea/editor.xml b/.idea/editor.xml
index 8d0e15e..51e9788 100644
--- a/.idea/editor.xml
+++ b/.idea/editor.xml
@@ -139,7 +139,7 @@
     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppNotAllPathsReturnValue/@EntryIndexedValue" value="WARNING" type="string" />
     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppObjectMemberMightNotBeInitialized/@EntryIndexedValue" value="WARNING" type="string" />
     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppOutParameterMustBeWritten/@EntryIndexedValue" value="WARNING" type="string" />
-    <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppParameterMayBeConst/@EntryIndexedValue" value="HINT" type="string" />
+    <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppParameterMayBeConst/@EntryIndexedValue" value="DO_NOT_SHOW" type="string" />
     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppParameterMayBeConstPtrOrRef/@EntryIndexedValue" value="SUGGESTION" type="string" />
     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppParameterNamesMismatch/@EntryIndexedValue" value="HINT" type="string" />
     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppParameterNeverUsed/@EntryIndexedValue" value="HINT" type="string" />
diff --git a/.idea/inspectionProfiles/Project_Default.xml b/.idea/inspectionProfiles/Project_Default.xml
new file mode 100644
index 0000000..702845c
--- /dev/null
+++ b/.idea/inspectionProfiles/Project_Default.xml
@@ -0,0 +1,6 @@
+<component name="InspectionProjectProfileManager">
+  <profile version="1.0">
+    <option name="myName" value="Project Default" />
+    <inspection_tool class="CppParameterMayBeConst" enabled="false" level="HINT" enabled_by_default="false" />
+  </profile>
+</component>
\ No newline at end of file
diff --git a/src/kernel/common.h b/src/kernel/common.h
new file mode 100644
index 0000000..073ce89
--- /dev/null
+++ b/src/kernel/common.h
@@ -0,0 +1,11 @@
+#ifndef COMMON_H
+#define COMMON_H
+
+/**
+ * Sends a kernel panic message through the UART and hang the core.
+ * @param format The format of the message
+ * @param ... The parameters of the message
+ */
+void panic(const char *format, ...);
+
+#endif
\ No newline at end of file
diff --git a/src/kernel/kernel.c b/src/kernel/kernel.c
index 4088254..f783d72 100644
--- a/src/kernel/kernel.c
+++ b/src/kernel/kernel.c
@@ -1,46 +1,12 @@
-/*
- * =====================================================================================
- *
- *       Filename:  kernel.c
- *
- *    Description:  Kernel entry point 
- *
- *        Version:  1.0
- *        Created:  2026-02-16 10:13:30 PM
- *       Revision:  none
- *       Compiler:  gcc
- *
- *         Author:  William Nolin, 
- *
- * =====================================================================================
- */
-#include <stdint.h>
-#include <stddef.h>
-
 #include "syscon.h"
+#include "uart.h"
 
-unsigned char *uart = (unsigned char *)0x10000000;
-void putchar(char c) {
-	*uart = c;
-	return;
-}
- 
-void print(const char * str) {
-	while(*str != '\0') {
-		putchar(*str);
-		str++;
-	}
-	return;
-}
+#define ARCH "RISC-V 64"
  
 void kmain(void) {
-	power_off();
+	uart_init();
+	uart_printf("Hello world, %s!\n", ARCH);
 
-	// print("Hello world!\r\n");
-	// while(1) {
-	// 	// Read input from the UART
-	// 	putchar(*uart);
-	// }
-	// return;
+	power_off();
 }
 
diff --git a/src/kernel/riscv64/common.c b/src/kernel/riscv64/common.c
new file mode 100644
index 0000000..0621732
--- /dev/null
+++ b/src/kernel/riscv64/common.c
@@ -0,0 +1,21 @@
+#include "../common.h"
+
+#include <stdarg.h>
+
+#include "../uart.h"
+
+void panic(const char *format, ...) {
+    uart_puts("Kernel panic!");
+    uart_puts("Reason:");
+
+    va_list args = nullptr;
+    va_start(args, format);
+
+    // Print the reason
+    uart_vprintf(format, args);
+
+    va_end(args);
+
+    // Hang
+    asm volatile("wfi");
+}
diff --git a/src/kernel/riscv64/qemu/syscon.c b/src/kernel/riscv64/qemu/syscon.c
index 2515271..82633d2 100644
--- a/src/kernel/riscv64/qemu/syscon.c
+++ b/src/kernel/riscv64/qemu/syscon.c
@@ -1,13 +1,16 @@
 #include <stdint.h>
 #include "../../syscon.h"
+#include "../../uart.h"
 
 // QEMU exposes a syscon-compatible device at address 0x1000000
 #define SYSCON_ADDR 0x100000
 
 void power_off() {
+    uart_puts("Power off requested");
     *(uint32_t *) SYSCON_ADDR = 0x5555;
 }
 
 void reboot() {
+    uart_puts("Reboot requested");
     *(uint32_t *) SYSCON_ADDR = 0x7777;
 }
diff --git a/src/kernel/riscv64/qemu/uart.c b/src/kernel/riscv64/qemu/uart.c
new file mode 100644
index 0000000..3056318
--- /dev/null
+++ b/src/kernel/riscv64/qemu/uart.c
@@ -0,0 +1,81 @@
+#include <stdint.h>
+#include "../../uart.h"
+
+// QEMU emulates the NS16550A UART
+// The UART is memory mapped at 0x1000000
+#define UART_ADDR 0x10000000
+
+void uart_init() {
+    volatile uint8_t *ptr = (uint8_t *) UART_ADDR;
+
+    // Set the word length to 8 bits
+    ptr[3] = 0b11;
+
+    // Enable FIFO
+    ptr[2] = 0b1;
+
+    // Enable receiver buffer interrupts
+    ptr[1] = 0b1;
+
+    // For real hardware, we would need to set a baud rate
+}
+
+void uart_putchar(const char c) {
+    *(uint8_t *) UART_ADDR = c;
+}
+
+static void uart_print(const char *str) {
+    while (*str) {
+        uart_putchar(*str);
+        str++;
+    }
+}
+
+void uart_puts(const char *line) {
+    uart_print(line);
+    uart_putchar('\n');
+}
+
+// Basic implementation of printf  supporting the following formats:
+//  - c: Character
+//  - s: String of characters
+//  - %: Literal '%'
+void uart_vprintf(const char *restrict format, va_list args) {
+    while (*format) {
+        if (*format == '%') {
+            // Ignore this character as it indicates the format of a parameter
+            format++;
+            if (!*format) {
+                // There is nothing after '%'
+                return;
+            }
+
+            switch (*format) {
+                case 'c': // Character
+                    uart_putchar(va_arg(args, int));
+                    break;
+                case 's': // String
+                    uart_print(va_arg(args, char*));
+                    break;
+                case '%': // Literal '%'
+                    uart_putchar('%');
+                    break;
+                default: // Unsupported format
+                    uart_putchar('%');
+                    uart_putchar(*format);
+                    break;
+            }
+        } else {
+            uart_putchar(*format);
+        }
+
+        format++;
+    }
+}
+
+void uart_printf(const char *restrict format, ...) {
+    va_list args = nullptr;
+    va_start(args, format);
+    uart_vprintf(format, args);
+    va_end(args);
+}
diff --git a/src/kernel/uart.c b/src/kernel/uart.c
deleted file mode 100644
index 21d8258..0000000
--- a/src/kernel/uart.c
+++ /dev/null
@@ -1,3 +0,0 @@
-//
-// Created by william on 2026-02-21.
-//
\ No newline at end of file
diff --git a/src/kernel/uart.h b/src/kernel/uart.h
new file mode 100644
index 0000000..d554399
--- /dev/null
+++ b/src/kernel/uart.h
@@ -0,0 +1,34 @@
+#ifndef UART_H
+#define UART_H
+#include <stdarg.h>
+
+/** Initializes a UART device. */
+void uart_init();
+
+/**
+ * Sends a character to the UART.
+ * @param c The character to put
+ */
+void uart_putchar(char c);
+
+/**
+ * Sends a line to the UART.
+ * @param line The line to put
+ */
+void uart_puts(const char *line);
+
+/**
+ * Sends a string to the UART following a format.
+ * @param format The format of the string
+ * @param args The parameters of the string
+ */
+void uart_vprintf(const char *restrict format, va_list args);
+
+/**
+ * Sends a string to the UART following a format.
+ * @param format The format of the string
+ * @param ... The parameters of the string
+ */
+void uart_printf(const char *restrict format, ...);
+
+#endif
\ No newline at end of file