Initial commit: Schunix as it stands before the SchOS rename

An x86-64 operating system built from xv6, now largely rewritten: SMP,
a copy-on-write root filesystem (SchFS), PCI/USB/virtio drivers, a TTF
rasteriser, and a Linux-numbered syscall ABI.

No history before this point -- the tree was never under version control.
This commit exists so the rename that follows has something to undo to.

kernel/dev/uart.c

@@ -0,0 +1,95 @@
+// Intel 8250 serial port (UART).
+
+#include "types.h"
+#include "defs.h"
+#include "irq.h"
+#include "param.h"
+#include "traps.h"
+#include "spinlock.h"
+#include "sleeplock.h"
+#include "fs.h"
+#include "file.h"
+#include "mmu.h"
+#include "proc.h"
+#include "x86.h"
+
+#define COM1    0x3f8
+
+static int uart;    // is there a uart?
+
+void
+uartearlyinit(void)
+{
+  char *p;
+
+  // Turn off the FIFO
+  outb(COM1+2, 0);
+
+  // 9600 baud, 8 data bits, 1 stop bit, parity off.
+  outb(COM1+3, 0x80);    // Unlock divisor
+  outb(COM1+0, 115200/9600);
+  outb(COM1+1, 0);
+  outb(COM1+3, 0x03);    // Lock divisor, 8 data bits.
+  outb(COM1+4, 0);
+  outb(COM1+1, 0x01);    // Enable receive interrupts.
+
+  // If status is 0xFF, no serial port.
+  if(inb(COM1+5) == 0xFF)
+    return;
+  uart = 1;
+
+
+
+  // Announce that we're here.
+  for(p="Schunix UART...\n"; *p; p++)
+    uartputc(*p);
+}
+
+// irq.c hands every handler an opaque argument, because a driver with two
+// controllers needs to know which one interrupted. There is only one COM1.
+static void
+uart_irq(void *arg)
+{
+  (void)arg;
+  uartintr();
+}
+
+void
+uartinit(void)
+{
+  if(!uart)
+    return;
+
+  // Acknowledge pre-existing interrupt conditions;
+  // enable interrupts.
+  inb(COM1+2);
+  inb(COM1+0);
+  irq_register(IRQ_COM1, uart_irq, 0, "serial", 0);
+}
+void
+uartputc(int c)
+{
+  int i;
+
+  if(!uart)
+    return;
+  for(i = 0; i < 128 && !(inb(COM1+5) & 0x20); i++)
+    microdelay(10);
+  outb(COM1+0, c);
+}
+
+static int
+uartgetc(void)
+{
+  if(!uart)
+    return -1;
+  if(!(inb(COM1+5) & 0x01))
+    return -1;
+  return inb(COM1+0);
+}
+
+void
+uartintr(void)
+{
+  consoleintr(uartgetc);
+}