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uart.c

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+// Intel 8250 serial port (UART).
+
+#include "types.h"
+#include "defs.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 uartinit(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;
+
+    // Acknowledge pre-existing interrupt conditions;
+    // enable interrupts.
+    inb(COM1 + 2);
+    inb(COM1 + 0);
+    ioapicenable(IRQ_COM1, 0);
+
+    // Announce that we're here.
+    for (p = "xv6...\n"; *p; p++) {
+        uartputc(*p);
+    }
+}
+
+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);
+}