run without lapic and ioapic, if they are not present

if no lapic available, use 8253pit for clock
now xv6 runs both on qemu (uniprocessor) and bochs (uniprocessor and MP)

8253pit.c

+#include "types.h"
+#include "x86.h"
+#include "defs.h"
+#include "traps.h"
+
+// Register definitions for the Intel
+// 8253/8254/82C54 Programmable Interval Timer (PIT).
+
+#define	IO_TIMER1	0x040		/* 8253 Timer #1 */
+#define	IO_TIMER2	0x048		/* 8253 Timer #2 (EISA only) */
+
+//
+// Frequency of all three count-down timers; (TIMER_FREQ/freq) is the
+// appropriate count to generate a frequency of freq hz.
+
+#define	TIMER_FREQ	1193182
+#define TIMER_DIV(x)	((TIMER_FREQ+(x)/2)/(x))
+
+#define	TIMER_CNTR0	(IO_TIMER1 + 0)	/* timer 0 counter port */
+#define	TIMER_CNTR1	(IO_TIMER1 + 1)	/* timer 1 counter port */
+#define	TIMER_CNTR2	(IO_TIMER1 + 2)	/* timer 2 counter port */
+#define	TIMER_MODE	(IO_TIMER1 + 3)	/* timer mode port */
+#define		TIMER_SEL0	0x00	/* select counter 0 */
+#define		TIMER_SEL1	0x40	/* select counter 1 */
+#define		TIMER_SEL2	0x80	/* select counter 2 */
+#define		TIMER_INTTC	0x00	/* mode 0, intr on terminal cnt */
+#define		TIMER_ONESHOT	0x02	/* mode 1, one shot */
+#define		TIMER_RATEGEN	0x04	/* mode 2, rate generator */
+#define		TIMER_SQWAVE	0x06	/* mode 3, square wave */
+#define		TIMER_SWSTROBE	0x08	/* mode 4, s/w triggered strobe */
+#define		TIMER_HWSTROBE	0x0a	/* mode 5, h/w triggered strobe */
+#define		TIMER_LATCH	0x00	/* latch counter for reading */
+#define		TIMER_LSB	0x10	/* r/w counter LSB */
+#define		TIMER_MSB	0x20	/* r/w counter MSB */
+#define		TIMER_16BIT	0x30	/* r/w counter 16 bits, LSB first */
+#define		TIMER_BCD	0x01	/* count in BCD */
+
+void
+pit8253_timerinit(void)
+{
+  // initialize 8253 clock to interrupt 100 times/sec
+  outb(TIMER_MODE, TIMER_SEL0 | TIMER_RATEGEN | TIMER_16BIT);
+  outb(IO_TIMER1, TIMER_DIV(100) % 256);
+  outb(IO_TIMER1, TIMER_DIV(100) / 256);
+  irq_setmask_8259A(irq_mask_8259A & ~(1<<IRQ_TIMER));
+}

Makefile

@@ -21,6 +21,7 @@ OBJS = \
 	vectors.o\
 	bio.o\
 	fs.o\
+	8253pit.o\
 
 # Cross-compiling (e.g., on Mac OS X)
 TOOLPREFIX = i386-jos-elf-

console.c

@@ -409,6 +409,7 @@ console_init()
   devsw[CONSOLE].d_write = console_write;
   devsw[CONSOLE].d_read = console_read;
 
+  irq_setmask_8259A(irq_mask_8259A & ~(1 << IRQ_KBD));
   ioapic_enable(IRQ_KBD, 0);
 
   use_console_lock = 1;

defs.h

@@ -49,9 +49,15 @@ int checkstring(uint);
 int putint(struct proc*, uint, int);
 
 // picirq.c
+extern ushort irq_mask_8259A;
 void pic_init(void);
+void irq_setmask_8259A(ushort);
+
+// 8253pit.c
+void pit8253_timerinit(void);
 
 // mp.c
+extern int ismp;
 void mp_init(void);
 void mp_startthem(void);
 int mp_bcpu(void);

ide.c

@@ -50,6 +50,7 @@ void
 ide_init(void)
 {
   initlock(&ide_lock, "ide");
+  irq_setmask_8259A(irq_mask_8259A & ~(1 << IRQ_IDE));
   ioapic_enable (IRQ_IDE, ncpu - 1);
   ide_wait_ready(0);
   disk_1_present = ide_probe_disk1();

ioapic.c

@@ -37,28 +37,30 @@ ioapic_init(void)
   uchar id;
   int i;
 
-  io = (struct ioapic*) IO_APIC_BASE;
-  l = ioapic_read(io, IOAPIC_VER);
-  nintr =  ((l & IOART_VER_MAXREDIR) >> MAXREDIRSHIFT) + 1;
-  id = ioapic_read(io, IOAPIC_ID) >> APIC_ID_SHIFT;
-  if(id != ioapic_id)
-    panic("ioapic_init: id isn't equal to ioapic_id\n");
-  for(i = 0; i < nintr; i++) {
-    // active-hi and edge-triggered for ISA interrupts
-    // Assume that pin 0 on the first I/O APIC is an ExtINT pin.
-    // Assume that pins 1-15 are ISA interrupts
-    l = ioapic_read(io, IOAPIC_REDTBL_LO(i));
-    l = l & ~IOART_INTMASK;  // allow INTs
-    l |= IOART_INTMSET;
-    l = l & ~IOART_INTPOL;   // active hi
-    l = l & ~IOART_TRGRMOD;  // edgee triggered
-    l = l & ~IOART_DELMOD;   // fixed
-    l = l & ~IOART_DESTMOD;  // physical mode
-    l = l | (IRQ_OFFSET + i); // vector
-    ioapic_write(io, IOAPIC_REDTBL_LO(i), l);
-    h = ioapic_read(io, IOAPIC_REDTBL_HI(i));
-    h &= ~IOART_DEST;
-    ioapic_write(io, IOAPIC_REDTBL_HI(i), h);
+  if (ismp) {
+    io = (struct ioapic*) IO_APIC_BASE;
+    l = ioapic_read(io, IOAPIC_VER);
+    nintr =  ((l & IOART_VER_MAXREDIR) >> MAXREDIRSHIFT) + 1;
+    id = ioapic_read(io, IOAPIC_ID) >> APIC_ID_SHIFT;
+    if(id != ioapic_id)
+      cprintf("ioapic_init: id isn't equal to ioapic_id; not a MP\n");
+    for(i = 0; i < nintr; i++) {
+      // active-hi and edge-triggered for ISA interrupts
+      // Assume that pin 0 on the first I/O APIC is an ExtINT pin.
+      // Assume that pins 1-15 are ISA interrupts
+      l = ioapic_read(io, IOAPIC_REDTBL_LO(i));
+      l = l & ~IOART_INTMASK;  // allow INTs
+      l |= IOART_INTMSET;
+      l = l & ~IOART_INTPOL;   // active hi
+      l = l & ~IOART_TRGRMOD;  // edgee triggered
+      l = l & ~IOART_DELMOD;   // fixed
+      l = l & ~IOART_DESTMOD;  // physical mode
+      l = l | (IRQ_OFFSET + i); // vector
+      ioapic_write(io, IOAPIC_REDTBL_LO(i), l);
+      h = ioapic_read(io, IOAPIC_REDTBL_HI(i));
+      h &= ~IOART_DEST;
+      ioapic_write(io, IOAPIC_REDTBL_HI(i), h);
+    }
   }
 }
 
@@ -67,13 +69,15 @@ ioapic_enable (int irq, int cpunum)
 {
   uint l, h;
   struct ioapic *io;
-
-  io = (struct ioapic*) IO_APIC_BASE;
-  l = ioapic_read(io, IOAPIC_REDTBL_LO(irq));
-  l = l & ~IOART_INTMASK;  // allow INTs
-  ioapic_write(io, IOAPIC_REDTBL_LO(irq), l);
-  h = ioapic_read(io, IOAPIC_REDTBL_HI(irq));
-  h &= ~IOART_DEST;
-  h |= (cpunum << APIC_ID_SHIFT);
-  ioapic_write(io, IOAPIC_REDTBL_HI(irq), h);
+  
+  if (ismp) {
+    io = (struct ioapic*) IO_APIC_BASE;
+    l = ioapic_read(io, IOAPIC_REDTBL_LO(irq));
+    l = l & ~IOART_INTMASK;  // allow INTs
+    ioapic_write(io, IOAPIC_REDTBL_LO(irq), l);
+    h = ioapic_read(io, IOAPIC_REDTBL_HI(irq));
+    h &= ~IOART_DEST;
+    h |= (cpunum << APIC_ID_SHIFT);
+    ioapic_write(io, IOAPIC_REDTBL_HI(irq), h);
+  }
 }

lapic.c

@@ -105,17 +105,20 @@ lapic_write(int r, int data)
 void
 lapic_timerinit(void)
 {
-  lapic_write(LAPIC_TDCR, LAPIC_X1);
-  lapic_write(LAPIC_TIMER, LAPIC_CLKIN | LAPIC_PERIODIC |
-                           (IRQ_OFFSET + IRQ_TIMER));
-  lapic_write(LAPIC_TCCR, 10000000);
-  lapic_write(LAPIC_TICR, 10000000);
+  if (lapicaddr) {
+    lapic_write(LAPIC_TDCR, LAPIC_X1);
+    lapic_write(LAPIC_TIMER, LAPIC_CLKIN | LAPIC_PERIODIC |
+		(IRQ_OFFSET + IRQ_TIMER));
+    lapic_write(LAPIC_TCCR, 10000000);
+    lapic_write(LAPIC_TICR, 10000000);
+  }
 }
 
 void
 lapic_timerintr(void)
 {
-  lapic_write(LAPIC_EOI, 0);
+  if (lapicaddr) 
+    lapic_write(LAPIC_EOI, 0);
 }
 
 void
@@ -123,6 +126,9 @@ lapic_init(int c)
 {
   uint r, lvt;
 
+  if (lapicaddr == 0) 
+    return;
+
   lapic_write(LAPIC_DFR, 0xFFFFFFFF);    // Set dst format register
   r = (lapic_read(LAPIC_ID)>>24) & 0xFF; // Read APIC ID
   lapic_write(LAPIC_LDR, (1<<r)<<24);    // Set logical dst register to r
@@ -155,25 +161,32 @@ lapic_init(int c)
 void
 lapic_enableintr(void)
 {
-  lapic_write(LAPIC_TPR, 0);
+  if (lapicaddr)
+    lapic_write(LAPIC_TPR, 0);
 }
 
 void
 lapic_disableintr(void)
 {
-  lapic_write(LAPIC_TPR, 0xFF);
+  if (lapicaddr)
+    lapic_write(LAPIC_TPR, 0xFF);
 }
 
 void
 lapic_eoi(void)
 {
-  lapic_write(LAPIC_EOI, 0);
+  if (lapicaddr)
+    lapic_write(LAPIC_EOI, 0);
 }
 
 int
 cpu(void)
 {
-  int x = (lapic_read(LAPIC_ID)>>24) & 0xFF;
+  int x;
+  if (lapicaddr) 
+    x = (lapic_read(LAPIC_ID)>>24) & 0xFF;
+  else 
+    x = 0;
   return x;
 }
 

main.c

@@ -71,8 +71,11 @@ main0(void)
   // start other CPUs
   mp_startthem();
 
-  // turn on timer and enable interrupts on the local APIC
-  lapic_timerinit();
+  // turn on timer
+  if (ismp) lapic_timerinit();
+  else pit8253_timerinit();
+
+  // enable interrupts on the local APIC
   lapic_enableintr();
 
   // Enable interrupts on this processor.

mp.c

@@ -30,6 +30,7 @@ static char *buses[] = {
 };
 
 struct cpu cpus[NCPU];
+int ismp;
 int ncpu;
 uchar ioapic_id;
 
@@ -124,8 +125,11 @@ mp_init(void)
   uchar byte;
 
   ncpu = 0;
-  if((r = mp_detect()) != 0)
+  if((r = mp_detect()) != 0) {
     return;
+  }
+
+  ismp = 1;
 
   // Run through the table saving information needed for starting
   // application processors and initialising any I/O APICs. The table
@@ -165,7 +169,7 @@ mp_init(void)
       p += sizeof(struct mpie);
       continue;
     default:
-      cprintf("mpinit: unknown PCMP type 0x%x (e-p 0x%x)\n", *p, e-p);
+      cprintf("mp_init: unknown PCMP type 0x%x (e-p 0x%x)\n", *p, e-p);
       while(p < e){
         cprintf("%uX ", *p);
         p++;

picirq.c

@@ -11,9 +11,9 @@
 
 // Current IRQ mask.
 // Initial IRQ mask has interrupt 2 enabled (for slave 8259A).
-static ushort irq_mask_8259A = 0xFFFF & ~(1<<IRQ_SLAVE);
+ushort irq_mask_8259A = 0xFFFF & ~(1<<IRQ_SLAVE);
 
-static void
+void
 irq_setmask_8259A(ushort mask)
 {
   irq_mask_8259A = mask;

runoff.list

@@ -60,3 +60,4 @@ lapic.c
 ioapic.c
 picirq.c
 console.c
+8253pit.c
\ No newline at end of file

traps.h

@@ -27,8 +27,8 @@
 
 #define IRQ_OFFSET      32      // IRQ 0 corresponds to int IRQ_OFFSET
 
+#define IRQ_TIMER        0
 #define IRQ_KBD          1
 #define IRQ_IDE         14
-#define IRQ_TIMER       18
 #define IRQ_ERROR       19
 #define IRQ_SPURIOUS    31