From 4f14d8d1e594bdf45e36a035f6c3fd4ca959711e Mon Sep 17 00:00:00 2001
From: Frans Kaashoek <kaashoek@mit.edu>
Date: Wed, 9 Aug 2017 07:43:06 -0400
Subject: [PATCH] Commit to running on an SMP (perhaps with only 1 core).
 Remove most code from picirq.c and remove timer.c completely.  Update
 runoff.list.

---
 Makefile    |  1 -
 console.c   |  1 -
 ide.c       |  1 -
 ioapic.c    |  6 -----
 main.c      |  4 +--
 mp.c        | 13 +++-------
 picirq.c    | 70 +----------------------------------------------------
 runoff.list |  2 --
 timer.c     | 32 ------------------------
 uart.c      |  1 -
 10 files changed, 6 insertions(+), 125 deletions(-)
 delete mode 100644 timer.c

diff --git a/Makefile b/Makefile
index c6159fe1ed..06eea5d291 100644
--- a/Makefile
+++ b/Makefile
@@ -22,7 +22,6 @@ OBJS = \
 	syscall.o\
 	sysfile.o\
 	sysproc.o\
-	timer.o\
 	trapasm.o\
 	trap.o\
 	uart.o\
diff --git a/console.c b/console.c
index ca00a5fa6a..a280d2ba60 100644
--- a/console.c
+++ b/console.c
@@ -294,7 +294,6 @@ consoleinit(void)
   devsw[CONSOLE].read = consoleread;
   cons.locking = 1;
 
-  picenable(IRQ_KBD);
   ioapicenable(IRQ_KBD, 0);
 }
 
diff --git a/ide.c b/ide.c
index 881fe0dce3..b4c0b1f771 100644
--- a/ide.c
+++ b/ide.c
@@ -53,7 +53,6 @@ ideinit(void)
   int i;
 
   initlock(&idelock, "ide");
-  picenable(IRQ_IDE);
   ioapicenable(IRQ_IDE, ncpu - 1);
   idewait(0);
 
diff --git a/ioapic.c b/ioapic.c
index 0e9116f9a5..cb0f015c6b 100644
--- a/ioapic.c
+++ b/ioapic.c
@@ -50,9 +50,6 @@ ioapicinit(void)
 {
   int i, id, maxintr;
 
-  if(!ismp)
-    return;
-
   ioapic = (volatile struct ioapic*)IOAPIC;
   maxintr = (ioapicread(REG_VER) >> 16) & 0xFF;
   id = ioapicread(REG_ID) >> 24;
@@ -70,9 +67,6 @@ ioapicinit(void)
 void
 ioapicenable(int irq, int cpunum)
 {
-  if(!ismp)
-    return;
-
   // Mark interrupt edge-triggered, active high,
   // enabled, and routed to the given cpunum,
   // which happens to be that cpu's APIC ID.
diff --git a/main.c b/main.c
index e5b7d6453e..6bdeab4e03 100644
--- a/main.c
+++ b/main.c
@@ -22,7 +22,7 @@ main(void)
   mpinit();        // detect other processors
   lapicinit();     // interrupt controller
   seginit();       // segment descriptors
-  picinit();       // another interrupt controller
+  picinit();       // disable pic
   ioapicinit();    // another interrupt controller
   consoleinit();   // console hardware
   uartinit();      // serial port
@@ -31,8 +31,6 @@ main(void)
   binit();         // buffer cache
   fileinit();      // file table
   ideinit();       // disk 
-  if(!ismp)
-    timerinit();   // uniprocessor timer
   startothers();   // start other processors
   kinit2(P2V(4*1024*1024), P2V(PHYSTOP)); // must come after startothers()
   userinit();      // first user process
diff --git a/mp.c b/mp.c
index ade8930b37..79bb0ada4d 100644
--- a/mp.c
+++ b/mp.c
@@ -12,7 +12,6 @@
 #include "proc.h"
 
 struct cpu cpus[NCPU];
-int ismp;
 int ncpu;
 uchar ioapicid;
 
@@ -93,13 +92,14 @@ void
 mpinit(void)
 {
   uchar *p, *e;
+  int ismp;
   struct mp *mp;
   struct mpconf *conf;
   struct mpproc *proc;
   struct mpioapic *ioapic;
 
   if((conf = mpconfig(&mp)) == 0)
-    return;
+    panic("Expect to run on an SMP");
   ismp = 1;
   lapic = (uint*)conf->lapicaddr;
   for(p=(uchar*)(conf+1), e=(uchar*)conf+conf->length; p<e; ){
@@ -127,13 +127,8 @@ mpinit(void)
       break;
     }
   }
-  if(!ismp){
-    // Didn't like what we found; fall back to no MP.
-    ncpu = 1;
-    lapic = 0;
-    ioapicid = 0;
-    return;
-  }
+  if(!ismp)
+    panic("Didn't find a suitable machine");
 
   if(mp->imcrp){
     // Bochs doesn't support IMCR, so this doesn't run on Bochs.
diff --git a/picirq.c b/picirq.c
index 69785a7a32..e26957f041 100644
--- a/picirq.c
+++ b/picirq.c
@@ -1,5 +1,3 @@
-// Intel 8259A programmable interrupt controllers.
-
 #include "types.h"
 #include "x86.h"
 #include "traps.h"
@@ -8,79 +6,13 @@
 #define IO_PIC1         0x20    // Master (IRQs 0-7)
 #define IO_PIC2         0xA0    // Slave (IRQs 8-15)
 
-#define IRQ_SLAVE       2       // IRQ at which slave connects to master
-
-// Current IRQ mask.
-// Initial IRQ mask has interrupt 2 enabled (for slave 8259A).
-static ushort irqmask = 0xFFFF & ~(1<<IRQ_SLAVE);
-
-static void
-picsetmask(ushort mask)
-{
-  irqmask = mask;
-  outb(IO_PIC1+1, mask);
-  outb(IO_PIC2+1, mask >> 8);
-}
-
-void
-picenable(int irq)
-{
-  picsetmask(irqmask & ~(1<<irq));
-}
-
-// Initialize the 8259A interrupt controllers.
+// Don't use the 8259A interrupt controllers.  Xv6 assumes SMP hardware.
 void
 picinit(void)
 {
   // mask all interrupts
   outb(IO_PIC1+1, 0xFF);
   outb(IO_PIC2+1, 0xFF);
-
-  // Set up master (8259A-1)
-
-  // ICW1:  0001g0hi
-  //    g:  0 = edge triggering, 1 = level triggering
-  //    h:  0 = cascaded PICs, 1 = master only
-  //    i:  0 = no ICW4, 1 = ICW4 required
-  outb(IO_PIC1, 0x11);
-
-  // ICW2:  Vector offset
-  outb(IO_PIC1+1, T_IRQ0);
-
-  // ICW3:  (master PIC) bit mask of IR lines connected to slaves
-  //        (slave PIC) 3-bit # of slave's connection to master
-  outb(IO_PIC1+1, 1<<IRQ_SLAVE);
-
-  // ICW4:  000nbmap
-  //    n:  1 = special fully nested mode
-  //    b:  1 = buffered mode
-  //    m:  0 = slave PIC, 1 = master PIC
-  //      (ignored when b is 0, as the master/slave role
-  //      can be hardwired).
-  //    a:  1 = Automatic EOI mode
-  //    p:  0 = MCS-80/85 mode, 1 = intel x86 mode
-  outb(IO_PIC1+1, 0x3);
-
-  // Set up slave (8259A-2)
-  outb(IO_PIC2, 0x11);                  // ICW1
-  outb(IO_PIC2+1, T_IRQ0 + 8);      // ICW2
-  outb(IO_PIC2+1, IRQ_SLAVE);           // ICW3
-  // NB Automatic EOI mode doesn't tend to work on the slave.
-  // Linux source code says it's "to be investigated".
-  outb(IO_PIC2+1, 0x3);                 // ICW4
-
-  // OCW3:  0ef01prs
-  //   ef:  0x = NOP, 10 = clear specific mask, 11 = set specific mask
-  //    p:  0 = no polling, 1 = polling mode
-  //   rs:  0x = NOP, 10 = read IRR, 11 = read ISR
-  outb(IO_PIC1, 0x68);             // clear specific mask
-  outb(IO_PIC1, 0x0a);             // read IRR by default
-
-  outb(IO_PIC2, 0x68);             // OCW3
-  outb(IO_PIC2, 0x0a);             // OCW3
-
-  if(irqmask != 0xFFFF)
-    picsetmask(irqmask);
 }
 
 //PAGEBREAK!
diff --git a/runoff.list b/runoff.list
index 3db70720a5..02d1b6522f 100644
--- a/runoff.list
+++ b/runoff.list
@@ -60,11 +60,9 @@ mp.h
 mp.c
 lapic.c
 ioapic.c
-picirq.c
 kbd.h
 kbd.c
 console.c
-timer.c
 uart.c
 
 # user-level
diff --git a/timer.c b/timer.c
deleted file mode 100644
index 8df75a98df..0000000000
--- a/timer.c
+++ /dev/null
@@ -1,32 +0,0 @@
-// Intel 8253/8254/82C54 Programmable Interval Timer (PIT).
-// Only used on uniprocessors;
-// SMP machines use the local APIC timer.
-
-#include "types.h"
-#include "defs.h"
-#include "traps.h"
-#include "x86.h"
-
-#define IO_TIMER1       0x040           // 8253 Timer #1
-
-// 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_MODE      (IO_TIMER1 + 3) // timer mode port
-#define TIMER_SEL0      0x00    // select counter 0
-#define TIMER_RATEGEN   0x04    // mode 2, rate generator
-#define TIMER_16BIT     0x30    // r/w counter 16 bits, LSB first
-
-void
-timerinit(void)
-{
-  // 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);
-  picenable(IRQ_TIMER);
-}
diff --git a/uart.c b/uart.c
index 84da397b73..b8946da2e4 100644
--- a/uart.c
+++ b/uart.c
@@ -41,7 +41,6 @@ uartinit(void)
   // enable interrupts.
   inb(COM1+2);
   inb(COM1+0);
-  picenable(IRQ_COM1);
   ioapicenable(IRQ_COM1, 0);
 
   // Announce that we're here.