uptime command and vga textmode scrolling

Makefile

@@ -19,7 +19,7 @@ ISO := Hazel.iso
 
 CFLAGS    := -ffreestanding -Wall -Wextra -Werror -I $(INCLUDEDIR) -I lib
 LDFLAGS   := -ffreestanding -nostdlib -lgcc -T kernel/kernel.ld
-QEMUFLAGS := -cdrom $(BUILDDIR)/$(ISO) -s -m 512M -serial stdio
+QEMUFLAGS := -cdrom $(BUILDDIR)/$(ISO) -s -m 512M -serial stdio -device virtio-gpu
 
 $(BUILDDIR)/$(KIMG): $(KOBJ) $(LOBJ)
 	$(CC) $^ -o $@ $(LDFLAGS)

include/kernel/acpi.h

@@ -111,8 +111,11 @@ typedef struct {
     struct GenericAddressStructure X_GPE1Block;
 } fadt_t;
 
+typedef _Bool bool;
+
 rsdp_t *acpi_find_rsdp();
 uint8_t acpi_checksum(void *s, int size);
 void *acpi_find_sdt(rsdt_t *rsdt, const char *sig);
+bool acpi_init();
 
 #endif

include/kernel/kernel.h

@@ -4,11 +4,17 @@
 #include <kernel/multiboot.h>
 #include <kernel/log.h>
 #include <kernel/task.h>
+#include <kernel/acpi.h>
 
 #define cpu_relax asm volatile ("pause" ::)
 #define CHECK_FLAG(x, n) (x & (1<<n))
 
+#define TRUE 1
+#define FALSE 0
+typedef _Bool bool;
+
 #define KERNEL_VMA 0xC0000000
+#define KERNEL_LMA 0x00010000
 
 typedef struct {
    multi_mmap_t *multi_mmap;
@@ -18,6 +24,7 @@ typedef struct {
    log_method_t log_method;
    uint64_t ticks;
    task_t *current_task;
+   rsdt_t *rsdt;
 } kernel_ctx_t;
 
 #define GDT_NULL 0

include/kernel/tty.h

@@ -0,0 +1,21 @@
+#ifndef HAZEL_TTY_H_
+#define HAZEL_TTY_H_
+
+#include <stdint.h>
+
+typedef enum {
+    DEV_COM1,
+    DEV_VGA_TXT,
+} dev_t;
+
+typedef struct {
+   dev_t dev;
+
+   uint8_t *output;
+   uint8_t *input;
+
+   uint32_t output_len;
+   uint32_t input_len;
+} tty_t;
+
+#endif

include/kernel/vga.h

@@ -0,0 +1,67 @@
+#ifndef HAZEL_VGA_H_
+#define HAZEL_VGA_H_
+
+
+#include <stdint.h>
+
+/*
+ * Location of the linear text buffer
+ * Used to directly modify text on screen
+ * 80 columns by 25 rows
+ */
+#define VGA_MEMORY_ADDR 0xb8000
+
+#define VGA_MAX_COLS 80
+#define VGA_MAX_ROWS 25
+
+#define CRTC_ADDR_PORT 0x3d4
+#define CRTC_DATA_PORT 0x3d5
+
+#define CRTC_CURSOR_LO_REGISTER 0x0f
+#define CRTC_CURSOR_HI_REGISTER 0x0e
+
+enum VGA_COLOR {
+    VGA_COLOR_BLACK = 0,
+    VGA_COLOR_BLUE = 1,
+    VGA_COLOR_GREEN = 2,
+    VGA_COLOR_CYAN = 3,
+    VGA_COLOR_RED = 4,
+    VGA_COLOR_MAGENTA = 5,
+    VGA_COLOR_BROWN = 6,
+    VGA_COLOR_LIGHT_GREY = 7,
+    VGA_COLOR_DARK_GREY = 8,
+    VGA_COLOR_LIGHT_BLUE = 9,
+    VGA_COLOR_LIGHT_GREEN = 10,
+    VGA_COLOR_LIGHT_CYAN = 11,
+    VGA_COLOR_LIGHT_RED = 12,
+    VGA_COLOR_LIGHT_MAGENTA = 13,
+    VGA_COLOR_LIGHT_BROWN = 14,
+    VGA_COLOR_WHITE = 15
+};
+
+/**
+ * @brief Gets the text-mode cursor's position.
+ *
+ * @return The position, not offset, of the cursor. Multiply this by two for the offset.
+ */
+uint16_t get_cursor_pos();
+
+
+/**
+ * @brief Sets the cursor's position in VGA text-mode.
+ *
+ * @param pos The position, not offset, of the cursor. Multiply by two for the offset.
+ */
+void set_cursor_pos(uint16_t pos);
+
+/**
+ * @brief Clears the screen in VGA text-mode by overwriting every character with a zero, then resets the cursor position.
+ */
+void clear_screen(void);
+
+void vga_putc(char c);
+void popchar();
+
+void set_color(enum VGA_COLOR col);
+
+#endif

kernel/acpi.c

@@ -1,6 +1,8 @@
 #include <kernel/acpi.h>
 #include <kernel/kernel.h>
 
+extern kernel_ctx_t ctx;
+
 rsdp_t *acpi_find_rsdp() {
     char *ptr = (char *)(KERNEL_VMA + BIOS_START);
     const char sig[RSDP_SIG_LEN] = RSDP_SIG;
@@ -38,3 +40,38 @@ void *acpi_find_sdt(rsdt_t *rsdt, const char *sig) {
     
     return 0;
 }
+
+bool acpi_init() {
+    rsdp_t *rsdp = acpi_find_rsdp();
+    if (!rsdp) {
+        LOG("Invalid RSDP\n");
+        return FALSE; 
+    }
+    if (!acpi_checksum(rsdp, sizeof(rsdp_t))) { 
+        LOG("Invalid RSDP checksum\n");
+        return FALSE;
+    }
+
+    if (rsdp->Revision == 0) LOG("Using ACPI version 1.0\n")
+    else if (rsdp->Revision == 2) {
+        LOG("ACPI versions higher than 1.0 are not currently supported!\n");
+        return FALSE;
+    }
+
+    rsdt_t *rsdt = (rsdt_t *)(rsdp->RsdtAddress);
+    if (!rsdt) {
+        LOG("Invalid RSDT\n");
+        return FALSE; 
+    }
+    if (!acpi_checksum(rsdt, rsdt->hdr.Length)) { 
+        LOG("Invalid RSDT checksum\n");
+        return FALSE;
+    }
+    ctx.rsdt = rsdt;
+    LOG("RSDT is valid\n");
+
+    void *mcfg = acpi_find_sdt(rsdt, "MCFG");
+    if (!mcfg) LOG("PCIe not supported\n");
+
+    return TRUE;
+}

kernel/init.asm

@@ -280,11 +280,13 @@ boot_page_tab: times 1024 dd 0
 extern syscall_read
 extern syscall_write
 extern syscall_reboot
+extern syscall_uptime
 global syscall_table
 syscall_table:
     dd syscall_read
     dd syscall_write
     dd syscall_reboot
+    dd syscall_uptime
 
 section .bss
 align 16

kernel/kernel.c

@@ -10,6 +10,7 @@
 #include <kernel/ps2.h>
 #include <kernel/acpi.h>
 #include <kernel/pci.h>
+#include <kernel/vga.h>
 #include <stdint.h>
 
 kernel_ctx_t ctx = {0};
@@ -34,8 +35,11 @@ extern uint32_t boot_page_tab[1024];
 void syscall_write(stack_frame_t r) {
     uint32_t fd  = r.edi;
     uint8_t *buf = (uint8_t *)r.esi;
+    int len = r.edx;
     if (fd == FD_STDOUT) {
-        LOG("%s", buf);
+        for (int i = 0; i < len; i++) {
+            vga_putc(buf[i]);
+        }
     } 
 }
 
@@ -62,8 +66,10 @@ void syscall_reboot(stack_frame_t r) {
 }
 
 void syscall_uptime(stack_frame_t r) {
-    uint64_t *buf = (uint64_t *)r.esi;
+    uint32_t *low = (uint32_t *)r.esi;
-    *buf = ctx.ticks;
+    uint32_t *high = (uint32_t *)r.edi;
+    *low = (uint32_t)ctx.ticks;
+    *high = (uint32_t)(ctx.ticks >> 32);
 }
 
 void exception_handler(int_stack_frame_t r) {
@@ -76,15 +82,20 @@ void exception_handler(int_stack_frame_t r) {
     if (r.int_no == 0xe) {
         uint32_t cr2 = 0;
         asm volatile ("mov %%cr2, %0" : "=r" (cr2));
+        LOG("CR2:     0x%08X\n", cr2)
 
-        if ((boot_page_dir[PAGE_DIR_INDEX(cr2)] & 0xFFFFF000) == 0) {
+        uint32_t cr3 = 0;
+        asm volatile ("mov %%cr3, %0" : "=r" (cr3));
+        uint32_t *page_dir = (uint32_t *)(KERNEL_VMA + cr3);
+
+        if ((page_dir[PAGE_DIR_INDEX(cr2)] & 0xFFFFF000) == 0) {
             LOG("Creating new page table\n");
             uint32_t *page_tab = mmap_find_first_free_block();
             if (!page_tab) for (;;) {}
             page_tab[PAGE_TAB_INDEX(cr2)] = (cr2 & 0xFFFFF000) | 7;
-            boot_page_dir[PAGE_DIR_INDEX(cr2)] = ((uint32_t)page_tab - KERNEL_VMA) | 7;
+            page_dir[PAGE_DIR_INDEX(cr2)] = ((uint32_t)page_tab - KERNEL_VMA) | 7;
         } else {
-            uint32_t *page_tab = (uint32_t *)(KERNEL_VMA + (boot_page_dir[PAGE_DIR_INDEX(cr2)] & 0xFFFFF000)); 
+            uint32_t *page_tab = (uint32_t *)(KERNEL_VMA + (page_dir[PAGE_DIR_INDEX(cr2)] & 0xFFFFF000)); 
             page_tab[PAGE_TAB_INDEX(cr2)] = (cr2 & 0xFFFFF000) | 7;
         }
     }
@@ -100,7 +111,7 @@ void idt_init(void) {
     for (int i = 0; i < 32; i++) {
         idt_encode_entry(idt, i, isr_stub_table[i], GDT_SEGMENT_SELECTOR(GDT_KERNEL_CODE, RING0), TRAP_GATE_32 | INT_RING0 | INT_PRESENT);
     }
-    idt_encode_entry(idt, 32, (uint32_t)pit_isr, GDT_SEGMENT_SELECTOR(GDT_KERNEL_CODE, RING0), TRAP_GATE_32 | INT_RING0 | INT_PRESENT);
+    idt_encode_entry(idt, 0x20, (uint32_t)pit_isr, GDT_SEGMENT_SELECTOR(GDT_KERNEL_CODE, RING0), TRAP_GATE_32 | INT_RING0 | INT_PRESENT);
     idt_encode_entry(idt, 0x21, (uint32_t)ps2_isr, GDT_SEGMENT_SELECTOR(GDT_KERNEL_CODE, RING0), TRAP_GATE_32 | INT_RING0 | INT_PRESENT);
     idt_encode_entry(idt, 0x80, (uint32_t)syscall_isr, GDT_SEGMENT_SELECTOR(GDT_USER_CODE, RING3), TRAP_GATE_32 | INT_RING3 | INT_PRESENT);
 
@@ -110,6 +121,7 @@ void idt_init(void) {
     asm volatile ("lidt %0" :: "m"(idtr));
 }
 
+
 void kernel(multiboot_info_t *info) {
     if (!CHECK_FLAG(info->flags, 3))  goto halt;   // Modules
     if (!CHECK_FLAG(info->flags, 6))  goto halt;   // Memory map
@@ -125,23 +137,8 @@ void kernel(multiboot_info_t *info) {
     if (!mmap_init()) goto halt;
     LOG("%d bytes of RAM detected\nCreated a %d byte large physical memory map at 0x%08X\n", ctx.mmap_size*BLOCK_SIZE*8, ctx.mmap_size, (uint32_t)ctx.mmap);
 
-    rsdp_t *rsdp = acpi_find_rsdp();
+    clear_screen();
-    if (!rsdp) goto halt;
+    acpi_init();
-    if (!acpi_checksum(rsdp, sizeof(rsdp_t))) goto halt;
-
-    if (rsdp->Revision == 0) LOG("Using ACPI version 1.0\n")
-    else if (rsdp->Revision == 2) {
-        LOG("ACPI versions higher than 1.0 are not currently supported!\n");
-        goto halt;
-    }
-
-    rsdt_t *rsdt = (rsdt_t *)(rsdp->RsdtAddress);
-    if (!rsdt) goto halt;
-    if (!acpi_checksum(rsdt, rsdt->hdr.Length)) goto halt;
-    LOG("RSDT is valid\n");
-
-    void *mcfg = acpi_find_sdt(rsdt, "MCFG");
-    if (!mcfg) LOG("PCIe not supported\n");
 
     for (int i = 0; i < 256; i++) {
         for (int j = 0; j < 32; j++) {
@@ -150,7 +147,7 @@ void kernel(multiboot_info_t *info) {
                 uint8_t class = (uint8_t)(w >> 8);
                 uint8_t subclass = (uint8_t)w;
                 if (class == 0xFF) continue;
-                LOG("Class: %04X | Subclass: %04X\n", class, subclass);
+                LOG("PCI Class: %04X | Subclass: %04X\n", class, subclass);
             }
         }
     }
@@ -180,31 +177,6 @@ void kernel(multiboot_info_t *info) {
     tss.ss = tss.ds = tss.es = tss.fs = tss.gs = GDT_SEGMENT_SELECTOR(GDT_USER_DATA, RING3);
     flush_tss(GDT_SEGMENT_SELECTOR(5, RING3));
 
-    /*
-       task_t task1 = {0};
-       task_t task2 = {0};
-       task1.cr3 = (uint32_t)boot_page_dir - KERNEL_VMA;
-       task1.next = (uint32_t *)&task2;
-       ctx.current_task = &task1;
-
-       uint32_t *stack = mmap_find_first_free_block();
-       asm volatile ("mov %%esp, %0" : "=r" (task1.esp));
-       stack[1023] = 0x207;
-       stack[1022] = 0x8;
-       stack[1021] = (uint32_t)test;
-       stack[1020] = 0xDEADBEEF;
-       stack[1019] = 0xDEADBEEF;
-       stack[1018] = 0xDEADBEEF;
-       stack[1017] = 0xDEADBEEF;
-       stack[1016] = 0xDEADBEEF;
-       stack[1015] = 0xDEADBEEF;
-       stack[1014] = 0xDEADBEEF;
-       stack[1013] = 0xDEADBEEF;
-       task2.esp = (uint32_t)stack + (0x1000 - 44);
-       task2.cr3 = (uint32_t)boot_page_dir - KERNEL_VMA;
-       task2.next = 0;
-       */
-
     multi_mod_t *init = (multi_mod_t *)(info->moduleaddress + KERNEL_VMA);
     elf_t *elf = (elf_t *)(init->mod_start+KERNEL_VMA);
     task_t task = {0};

kernel/log.c

@@ -1,6 +1,7 @@
 #include <kernel/log.h>
 #include <kernel/kernel.h>
 #include <kernel/serial.h>
+#include <kernel/vga.h>
 
 extern kernel_ctx_t ctx;
 

kernel/ps2.c

@@ -2,6 +2,7 @@
 #include <kernel/io.h>
 #include <kernel/pic.h>
 #include <kernel/mem.h>
+#include <kernel/vga.h>
 
 extern kernel_ctx_t ctx;
 char shell_buffer[512] = {0};
@@ -52,7 +53,11 @@ void ps2_init() {
 
 void push_stdin(const char c) {
     ctx.current_task->stdin[ctx.current_task->stdin_len++] = c;
-    _putchar(c);
+    vga_putc(c);
+}
+
+void pop_stdin() {
+    ctx.current_task->stdin[--ctx.current_task->stdin_len] = 0;
 }
 
 void ps2_handler() {
@@ -100,11 +105,10 @@ void ps2_handler() {
             push_stdin('=');
             break;
         case KBD_BACKSPACE:
-            /*
+            if (ctx.current_task->stdin_len > 0) {
-               if (shell_index > 0) {
+                popchar();
-            //popchar();
+                pop_stdin();
-            shell_buffer[--shell_index] = 0;
+            }
-            }*/
             break;
         case KBD_TAB:
             break;

kernel/task.c

@@ -10,23 +10,8 @@ int task_init(task_t *task, elf_t *elf) {
 
     if (!elf) return 0;
     uint8_t *s = (uint8_t *)mmap_find_first_free_block();
-    /*
-       memset(s, 0, 0x1000);
-       int idx = 0;
-    // Loop section header to find ALLOC sections then allocate them
-    for (int i = 0; i < elf->e_shnum; i++) {
-    section_t *sec = (section_t *)((uint32_t)elf + elf->e_shoff + i*elf->e_shentsize);
-    if (!(sec->sh_flags & 0x2)) continue;
-    if (!sec->sh_addr) continue;
-    idx += sec->sh_offset;
-    memcpy(s + idx, (void *)((uint32_t)elf + sec->sh_offset), sec->sh_offset);
-    LOG("%d\n", sec->sh_offset);
-    }
-    */
     memcpy(s, elf, 0x1000);
 
-    //section_t *text = elf_find_section(elf, ".text");
-    //if (!text) return 0;
     task->eip = elf->e_entry;
     // Allocate a page for a stack
     task->esp = (uint32_t)mmap_find_first_free_block() + 0x1000;
@@ -47,16 +32,7 @@ int task_init(task_t *task, elf_t *elf) {
         else page_dir[i] = 6;
     }
     // Map the ELF image to its specified entry
-    // This will cause problems if the ELF image is larger than 4 MiB so I need to fix this
-    //page_dir[PAGE_DIR_INDEX(elf->e_entry)] = ((uint32_t)page_tab - KERNEL_VMA) | 7;
     page_dir[PAGE_DIR_INDEX(elf->e_entry)] = ((uint32_t)page_tab - KERNEL_VMA) | 7;
-
-    /*
-       uint32_t elf_phys = (uint32_t)s - KERNEL_VMA;
-       for (int i = 0; i < 1024; i++) {
-       page_tab[i] = (elf_phys + 0x1000*i) | 7;
-       }
-       */
     page_tab[PAGE_TAB_INDEX(elf->e_entry)] = ((uint32_t)s - KERNEL_VMA) | 7;
 
     return 1;

kernel/tty.c

@@ -0,0 +1,14 @@
+#include <kernel/serial.h>
+#include <kernel/tty.h>
+
+void tty_putc(tty_t *tty, char c) {
+    switch (tty->dev) {
+        case DEV_COM1:
+            serial_putc(COM1, c);
+            break;
+        case DEV_VGA_TXT:
+            break;
+        default:
+            break;
+    }
+}

kernel/vga.c

@@ -0,0 +1,98 @@
+/**
+ * @file vga.c
+ * @brief Basic functions for interacting with the CRTC controller in VGA text-mode.
+ * @author rami
+ * @version 0.1
+ * @date 2024-02-03
+ */
+
+#include <kernel/vga.h>
+#include <kernel/io.h>
+#include <kernel/log.h>
+#include <kernel/mem.h>
+
+enum VGA_COLOR vga_color = VGA_COLOR_WHITE;
+
+uint16_t get_cursor_pos() {
+    uint16_t pos = 0;
+
+    /* Tell CRTC controller we want the low cursor position */
+    outb(CRTC_ADDR_PORT, CRTC_CURSOR_LO_REGISTER);
+    /* Read it through the data port */
+    pos = inb(CRTC_DATA_PORT);
+    
+    /* Repeat with high position */
+    outb(CRTC_ADDR_PORT, CRTC_CURSOR_HI_REGISTER);
+    uint16_t hi_pos = 0;
+    hi_pos = inb(CRTC_DATA_PORT);
+    pos |= hi_pos << 8;
+
+    return pos;
+}
+
+void set_cursor_pos(uint16_t pos) {
+    /* Tell CRTC controller we want the low cursor position */
+    outb(CRTC_ADDR_PORT, CRTC_CURSOR_LO_REGISTER);
+    outb(CRTC_DATA_PORT, (uint8_t)(pos & 0xFF));
+    /* Repeat with high position */
+    outb(CRTC_ADDR_PORT, CRTC_CURSOR_HI_REGISTER);
+    outb(CRTC_DATA_PORT, (uint8_t)((pos >> 8) & 0xFF));
+}
+
+void clear_screen(void) {
+    char *video_memory = (char *)VGA_MEMORY_ADDR;
+    for (int i = 0; i < VGA_MAX_COLS * VGA_MAX_ROWS; i++) {
+       video_memory[i * 2] = 0;
+    }
+
+    set_cursor_pos(0);
+}
+
+void vga_putc(char character) {
+    uint16_t pos = get_cursor_pos();
+
+    if (pos == VGA_MAX_COLS * VGA_MAX_ROWS) {
+        if (character != '\n') {
+            // Move video memory up one row
+            memcpy((char*)VGA_MEMORY_ADDR, (char *)(VGA_MEMORY_ADDR + VGA_MAX_COLS*2), VGA_MAX_COLS * (VGA_MAX_ROWS - 1) * 2);
+            // Clear last row
+            for (int i = 0; i < VGA_MAX_COLS*2; i+=2) {
+                ((char *)(VGA_MEMORY_ADDR + VGA_MAX_COLS*(VGA_MAX_ROWS - 1)*2))[i] = 0;
+                ((char *)(VGA_MEMORY_ADDR + VGA_MAX_COLS*(VGA_MAX_ROWS - 1)*2))[i+1] = 0x0f;
+            }
+            pos = VGA_MAX_COLS * (VGA_MAX_ROWS - 1);
+        } else {
+            // Move video memory up two rows
+            memcpy((char*)VGA_MEMORY_ADDR, (char *)(VGA_MEMORY_ADDR + VGA_MAX_COLS*2*2), VGA_MAX_COLS * (VGA_MAX_ROWS - 2) * 2);
+            // Clear last 2 rows
+            for (int i = 0; i < VGA_MAX_COLS*2*2; i+=2) {
+                ((char *)(VGA_MEMORY_ADDR + VGA_MAX_COLS*(VGA_MAX_ROWS - 2)*2))[i] = 0;
+                ((char *)(VGA_MEMORY_ADDR + VGA_MAX_COLS*(VGA_MAX_ROWS - 2)*2))[i+1] = 0x0f;
+            }
+            pos = VGA_MAX_COLS * (VGA_MAX_ROWS - 2);
+        }
+    }
+
+    char *video_memory = (char *)VGA_MEMORY_ADDR + pos * 2;
+
+    if (character == '\n') {
+        uint16_t next_line = VGA_MAX_COLS * (pos / VGA_MAX_COLS + 1);
+        set_cursor_pos(next_line);
+    } else {
+        video_memory[0] = character;
+        video_memory[1] = vga_color;
+        set_cursor_pos(pos + 1);
+    }
+}
+
+void popchar() {
+    uint16_t pos = get_cursor_pos();
+    if (pos == 0) return;
+    char *video_memory = (char *)(VGA_MEMORY_ADDR + (pos - 1) * 2);
+    video_memory[0] = 0;
+    set_cursor_pos(pos - 1);
+}
+
+void set_color(enum VGA_COLOR col) {
+    vga_color = col;
+}

user/shell.c

@@ -1,14 +1,36 @@
 #include "../lib/strcmp.h"
 
+int strlen(const char *str) {
+    const char *s;
+    for (s = str; *s; s++)
+        ;
+
+    return s - str;
+}
+
+void putc(const char c) {
+    asm volatile (
+	    "movl $1, %%eax\n\t"
+	    "movl $1, %%edi\n\t"
+	    "movl %0, %%esi\n\t"
+	    "movl $1, %%edx\n\t"
+	    "int $0x80"
+	    : 
+	    : "r"(&c)
+	    : "%eax", "%edi", "%esi", "%edx"
+	    );
+}
+
 void puts(const char *str) {
     asm volatile (
 	    "movl $1, %%eax\n\t"
 	    "movl $1, %%edi\n\t"
 	    "movl %0, %%esi\n\t"
+	    "movl %1, %%edx\n\t"
 	    "int $0x80"
 	    : 
-	    : "r"(str) 
+	    : "r"(str), "r"(strlen(str))
-	    : "%eax", "%edi", "%esi"
+	    : "%eax", "%edi", "%esi", "%edx"
 	    );
 }
 
@@ -32,18 +54,50 @@ void reboot() {
 	    );
 }
 
+uint64_t uptime() {
+    uint32_t low = 0;
+    uint32_t high = 0;
+    asm volatile (
+	    "movl $3, %%eax\n\t"
+	    "movl %0, %%esi\n\t"
+	    "movl %1, %%edi\n\t"
+	    "int $0x80"
+	    : 
+	    : "r" (&low), "r" (&high)
+	    : "eax", "esi"
+	    );
+
+    return (uint64_t)low | ((uint64_t)high << 32);
+}
+
 extern char *buf;
 
+void print_int(int num){
+    if (num < 0)
+    {
+       putc('-');
+       num = -num;
+    }
+
+    if (num > 9) print_int(num/10);
+
+    putc(('0'+ (num%10)));
+ }
+
 void _start() {
     char buf1[256] = {0};
     puts("Welcome to the Hazel user shell!\n");
     while (1) {
-	puts("> ");
+	puts("$ ");
 	read(0, buf1, 256);
         if (!strcmp(buf1, "SKIBIDI")) {
             puts("dop dop yes yes!\n");
         } else if (!strcmp(buf1, "REBOOT")) {
             reboot();
+        } else if (!strcmp(buf1, "UPTIME")) {
+            uint64_t ticks = uptime();
+            print_int(ticks);
+            puts("\n");
         }
         else {
             puts("unknown command!\n");