add some comments

find out the hard way why user and kernel must have separate segment descriptors

1 files changed, 12 insertions, 10 deletions

diff --git a/main.c b/main.c
index 8be66e3..a6088cb 100644
--- a/main.c
+++ b/main.c
@@ -16,13 +16,13 @@ main(void)
 {
   mpinit();        // collect info about this machine
   lapicinit(mpbcpu());
-  ksegment();
+  ksegment();      // set up segments
   picinit();       // interrupt controller
   ioapicinit();    // another interrupt controller
   consoleinit();   // I/O devices & their interrupts
   uartinit();      // serial port
-  pminit();        // physical memory for kernel
-  jkstack();       // Jump to mainc on a properly-allocated stack 
+  pminit();        // discover how much memory there is
+  jkstack();       // call mainc() on a properly-allocated stack 
 }
 
 void
@@ -41,7 +41,7 @@ void
 mainc(void)
 {
   cprintf("\ncpu%d: starting xv6\n\n", cpu->id);
-  kvmalloc();      // allocate the kernel page table
+  kvmalloc();      // initialze the kernel page table
   pinit();         // process table
   tvinit();        // trap vectors
   binit();         // buffer cache
@@ -57,8 +57,9 @@ mainc(void)
   mpmain();
 }
 
-// Bootstrap processor gets here after setting up the hardware.
-// Additional processors start here.
+// Common CPU setup code.
+// Bootstrap CPU comes here from mainc().
+// Other CPUs jump here from bootother.S.
 static void
 mpmain(void)
 {
@@ -66,11 +67,11 @@ mpmain(void)
     ksegment();
     lapicinit(cpunum());
   }
-  vminit();        // Run with paging on each processor
+  vminit();        // turn on paging
   cprintf("cpu%d: starting\n", cpu->id);
-  idtinit();
+  idtinit();       // load idt register
   xchg(&cpu->booted, 1);
-  scheduler();
+  scheduler();     // start running processes
 }
 
 static void
@@ -85,6 +86,7 @@ bootothers(void)
   // placed the start of bootother.S there.
   code = (uchar *) 0x7000;
   memmove(code, _binary_bootother_start, (uint)_binary_bootother_size);
+
   for(c = cpus; c < cpus+ncpu; c++){
     if(c == cpus+cpunum())  // We've started already.
       continue;
@@ -95,7 +97,7 @@ bootothers(void)
     *(void**)(code-8) = mpmain;
     lapicstartap(c->id, (uint)code);
 
-    // Wait for cpu to get through bootstrap.
+    // Wait for cpu to finish mpmain()
     while(c->booted == 0)
       ;
   }