SchOS/kernel/gmmos/ps2.c

// SPDX-License-Identifier: GPL-2.0-or-later
//
// GMMOS's PS/2 keyboard: kernel/dev/kbd.c with everything but the keys taken
// out.
//
// No interrupt: the status port is polled. That also makes it immune to the
// IRQ 1 polarity quirk of some AMD laptops -- the ASUS TUF among them -- which
// is about how the interrupt is routed, and nothing here is routed. No
// /dev/input, no grab, no terminal chords. Scancode set 1, as the controller
// translates it, through the same keymap the console uses.

#include "core/types.h"
#include "arch/x86.h"
#include "core/defs.h"
#include "dev/kbd.h"
#include "dev/keymap.h"
#include "gmmos/gmmos.h"

// kbd.c's tables, which are static there. Hardware facts, so they are short.
static const uchar shiftcode[256] = {
  [0x1D] = CTL, [0x2A] = SHIFT, [0x36] = SHIFT, [0x38] = ALT,
  [0x9D] = CTL, [0xB8] = RALT,
};
static const uchar togglecode[256] = {
  [0x3A] = CAPSLOCK, [0x45] = NUMLOCK, [0x46] = SCROLLLOCK,
};

static uint shift;
static int  e0, e1skip;

// Bytes that arrived while a command was waiting for its answer. Setting the
// lights is a command, and a key pressed during it would otherwise be eaten.
static uchar held[16];
static int   nheld, iheld;

// A byte from the controller, or -1. A byte from the mouse is read too -- left
// in the buffer, it blocks every keyboard byte behind it -- and dropped.
static int
rd(void)
{
  uint st = inb(KBSTATP);
  if (!(st & KBS_DIB))
    return -1;
  uchar d = inb(KBDATAP);
  if (st & 0x20)
    return -1;
  return d;
}

static void
wr(uchar b)
{
  for (int i = 0; i < 10000; i++) {
    if (!(inb(KBSTATP) & 0x02)) {
      outb(KBDATAP, b);
      return;
    }
    microdelay(10);
  }
}

// Wait up to 20 ms for the keyboard's answer to a command, keeping anything
// else that arrives first.
static void
answer(void)
{
  for (int i = 0; i < 2000; i++) {
    int d = rd();
    if (d < 0) {
      microdelay(10);
      continue;
    }
    if (d == 0xFA || d == 0xFE)
      return;
    if (nheld < (int)sizeof(held))
      held[nheld++] = (uchar)d;
  }
}

static int
probe(void)
{
  // No controller decodes the port: every bit reads as one.
  if (inb(KBSTATP) == 0xFF)
    return 0;
  for (int i = 0; i < 64 && (inb(KBSTATP) & KBS_DIB); i++)
    (void)inb(KBDATAP);
  shift = 0;
  e0 = e1skip = 0;

  // A controller with no keyboard behind it -- a desktop with only USB ones
  // -- must not be offered as one: GMMOS would list keys that do nothing. So
  // ask the keyboard itself to echo, and wait 50 ms for it to.
  wr(0xEE);
  for (int i = 0; i < 5000; i++) {
    int d = rd();
    if (d == 0xEE)
      return 1;
    if (d < 0)
      microdelay(10);
  }
  return 0;
}

static void
leds(int on)
{
  wr(0xED);
  answer();
  wr(on ? 0x07 : 0x00);
  answer();
}

static int
poll(void)
{
  int d;

  if (iheld < nheld) {
    d = held[iheld++];
  } else {
    nheld = iheld = 0;
    d = rd();
  }
  if (d < 0)
    return 0;

  // Answers and self-test results, not keys.
  if (d == 0xFA || d == 0xFE || d == 0xAA || d == 0xEE || d == 0x00 || d == 0xFF)
    return 0;
  // Pause is E1 1D 45 E1 9D C5, and means nothing here. Read as keys, it
  // would be a Ctrl press and two Num Lock toggles.
  if (e1skip) {
    e1skip--;
    return 0;
  }
  if (d == 0xE1) {
    e1skip = 5;
    return 0;
  }
  if (d == 0xE0) {
    e0 = 1;
    return 0;
  }

  // As in kbdgetc: a release clears its modifier, a press with E0 before it
  // is looked up with the high bit set.
  if (d & 0x80) {
    d = e0 ? d : (d & 0x7F);
    shift &= ~shiftcode[d];
    e0 = 0;
    return 0;
  }
  if (e0) {
    d |= 0x80;
    e0 = 0;
  }
  shift |= shiftcode[d];
  shift ^= togglecode[d];

  return (int)keymap_lookup((uint)d, shift);
}

const struct gmmos_kbd gmmos_ps2 = {
  .name  = "PS/2",
  .probe = probe,
  .poll  = poll,
  .leds  = leds,
};