fix: backspace behavior

kernel/core/kmain.c

@@ -2,30 +2,157 @@
  *
  * Called once from the stage-2 entry stub after the CPU is in 64-bit long
  * mode with a valid stack, zeroed BSS and identity-mapped memory. Runs at
- * Ring 0 (CPL 0) interrupts disabled. Installs the exception IDT first
+ * Ring 0 (CPL 0) with IF=0 on entry under the stage-2 GDT (CS 0x18);
- * so from then on a fault prints diagnostics instead of triple-faulting.
+ * `-mno-red-zone` keeps IRQ pushes off the red zone so interrupt frames
- * It never returns; on return the caller halts the CPU.
+ * are safe. Installs the exception IDT first so from then on a fault
+ * prints diagnostics instead of triple-faulting. `sti` runs exactly once
+ * after every device is programmed; the main loop keeps IF=1 and sleeps
+ * in `hlt` (which wakes on each IRQ) — never `cli`-parks, or timer ticks
+ * and keystrokes would stop. It never returns; on return the caller halts.
  */
 
+#include <stdint.h>
+
 #include "console.h"
 #include "idt.h"
+#include "keyboard.h"
+#include "pic.h"
+#include "pit.h"
+#include "serial.h"
 
 /* A value that only comes out right if the CPU truly executes 64-bit
  * arithmetic: every nibble survives the shifts above 32 bits. */
 #define PROOF_VALUE 0x0123456789ABCDEFULL
 
+/* Print an unsigned decimal via console_putchar (no libc printf). */
+static void print_dec(uint64_t v)
+{
+    char buf[20];
+    int n = 0;
+
+    if (v == 0) {
+        console_putchar('0');
+        return;
+    }
+    while (v != 0 && n < (int)sizeof(buf)) {
+        buf[n++] = (char)('0' + (v % 10U));
+        v /= 10U;
+    }
+    while (n > 0) {
+        n--;
+        console_putchar(buf[n]);
+    }
+}
+
+/* Mirror one echoed keystroke to COM1 when the UART looks present. */
+static void serial_echo(char c, int ok)
+{
+    char tmp[2];
+
+    if (ok == 0) {
+        return;
+    }
+    if (c == '\b') {
+        /* Erase on a serial terminal: back, blank, back. */
+        serial_puts("\b \b");
+    } else if (c == '\n') {
+        serial_puts("\r\n");
+    } else {
+        tmp[0] = c;
+        tmp[1] = '\0';
+        serial_puts(tmp);
+    }
+}
+
 void kmain(void)
 {
+    int serial_present;
+    uint64_t last_uptime;
+
     console_clear();
     console_puts("Hello World from Nadir Kernel !\n");
     console_puts("Running C code in 64-bit long mode (Ring 0).\n");
+
+    /* WHY this order: pic_remap must precede idt_install_irqs so IRQ
+     * gates land on valid remapped vectors 32-47 (pre-remap they would
+     * overlap CPU exceptions 0-15 and a tick would look like a fault);
+     * devices (serial/PIT/keyboard) are programmed before sti so no IRQ
+     * fires into a half-wired handler; pic_remap masks everything and
+     * each device opts in via pic_unmask, so stray lines stay silent. */
     idt_init();
     console_puts("IDT installed (vectors 0-31).\n");
+
+    pic_remap();
+    console_puts("PIC remapped (IRQ 0-15 -> vectors 32-47, masked).\n");
+
+    idt_install_irqs();
+    console_puts("IRQ gates installed (vectors 32-47).\n");
+
+    serial_init();
+    serial_present = serial_ok();
+    console_puts("Serial COM1 38400 8N1 ready.\n");
+    if (serial_present != 0) {
+        serial_puts("Hello World from Nadir Kernel !\n");
+        serial_puts("Serial COM1 38400 8N1 ready.\n");
+    }
+
+    pit_init();
+    console_puts("PIT 100Hz on IRQ0 ready.\n");
+    if (serial_present != 0) {
+        serial_puts("PIT 100Hz on IRQ0 ready.\n");
+    }
+
+    keyboard_init();
+    console_puts("Keyboard PS/2 IRQ1 ready.\n");
+    if (serial_present != 0) {
+        serial_puts("Keyboard PS/2 IRQ1 ready.\n");
+    }
+
+    /* Explicit opt-in for the two live lines; idempotent even though
+     * keyboard_init already unmasked IRQ1. */
+    pic_unmask(0);
+    pic_unmask(1);
+
+    __asm__ volatile("sti");
+    console_puts("Interrupts enabled (IRQs 0-1).\n");
+    if (serial_present != 0) {
+        serial_puts("Interrupts enabled (IRQs 0-1).\n");
+    }
+
     console_puts("64-bit proof value: ");
     console_puthex64(PROOF_VALUE);
-    console_puts("\nHalting.\n");
+    console_puts("\nHalting in hlt loop (timer + keyboard live).\n");
 
+    /* Main loop: hlt sleeps until the next IRQ (IF=1 throughout), then
+     * one poll pass prints uptime ~1/s and drains echoed keys. */
+    last_uptime = 0;
     for (;;) {
+        uint64_t now;
+
         __asm__ volatile("hlt");
+        now = pit_ticks();
+        if ((now - last_uptime) >= 100U) {
+            uint64_t secs = now / 100U;
+            uint64_t tenths = (now / 10U) % 10U;
+
+            last_uptime = now;
+            console_puts("uptime ");
+            print_dec(secs);
+            console_puts(".");
+            print_dec(tenths);
+            console_puts("s (ticks ");
+            console_puthex64(now);
+            console_puts(")\n");
+            if (serial_present != 0) {
+                serial_puts("uptime (see VGA for value)\n");
+            }
+        }
+        while (keyboard_has_key() != 0) {
+            char c = keyboard_dequeue();
+
+            /* console_putchar erases on '\b' and wraps on '\n'. */
+            console_putchar(c);
+            serial_echo(c, serial_present);
+        }
     }
 }