Record networking and DMA development progress

Add the current OS source tree, build scripts, system image layout, and development notes covering DMA page allocation, e1000 bring-up, net API dispatch, and DHCP work in progress.

CODE/UTSM/arch/x86_64/serial.c

@@ -0,0 +1,45 @@
+#include <utsm/types.h>
+
+void outb(u16 port, u8 value);
+u8 inb(u16 port);
+
+#define COM1 0x3F8
+
+static int serial_ready(void) {
+    return (inb(COM1 + 5) & 0x20) != 0;
+}
+
+static int serial_wait_ready(void) {
+    for (u64 spin = 0; spin < 1000000ULL; spin++) {
+        if (serial_ready()) {
+            return 1;
+        }
+    }
+    return 0;
+}
+
+void serial_init(void) {
+    outb(COM1 + 1, 0x00);
+    outb(COM1 + 3, 0x80);
+    outb(COM1 + 0, 0x03);
+    outb(COM1 + 1, 0x00);
+    outb(COM1 + 3, 0x03);
+    outb(COM1 + 2, 0xC7);
+    outb(COM1 + 4, 0x0B);
+}
+
+void serial_putc(char c) {
+    if (c == '\n') {
+        serial_putc('\r');
+    }
+    if (!serial_wait_ready()) {
+        return;
+    }
+    outb(COM1, (u8)c);
+}
+
+void serial_write(const char *s) {
+    while (*s) {
+        serial_putc(*s++);
+    }
+}