From: Ben Pfaff <blp@cs.stanford.edu>
Date: Thu, 2 Sep 2004 23:27:56 +0000 (+0000)
Subject: Reorganization, comments.
X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?p=pintos-anon;a=commitdiff_plain;h=7180597203a54c08582b1bb092dc465ec1d26d7c

Reorganization, comments.
---

diff --git a/src/devices/serial.c b/src/devices/serial.c
index 8d1633f..e5b2fb7 100644
--- a/src/devices/serial.c
+++ b/src/devices/serial.c
@@ -4,23 +4,9 @@
 #include "io.h"
 #include "timer.h"
 
-static void
-set_serial (int bps, int bits, enum parity_type parity, int stop)
-{
-  int baud_base = 1843200 / 16;         /* Base rate of 16550A. */
-  uint16_t divisor = baud_base / bps;   /* Clock rate divisor. */
-    
-  /* Enable DLAB. */
-  outb (LCR_REG, make_lcr (bits, parity, stop, false, true));
-
-  /* Set baud rate. */
-  outb (LS_REG, divisor & 0xff);
-  outb (MS_REG, divisor >> 8);
-  
-  /* Reset DLAB. */
-  outb (LCR_REG, make_lcr (bits, parity, stop, false, false));
-}
+static void set_serial (int bps, int bits, enum parity_type parity, int stop);
 
+/* Initializes the serial port device. */
 void
 serial_init (void) 
 {
@@ -30,6 +16,7 @@ serial_init (void)
   outb (MCR_REG, 0);    /* Turn off output lines. */
 }
 
+/* Sends BYTE to the serial port. */
 void
 serial_outb (uint8_t byte) 
 {
@@ -37,3 +24,22 @@ serial_outb (uint8_t byte)
     continue;
   outb (THR_REG, byte);
 }
+
+/* Configures the first serial port for BPS bits per second,
+   BITS bits per byte, the given PARITY, and STOP stop bits. */
+static void
+set_serial (int bps, int bits, enum parity_type parity, int stop)
+{
+  int baud_base = 1843200 / 16;         /* Base rate of 16550A. */
+  uint16_t divisor = baud_base / bps;   /* Clock rate divisor. */
+    
+  /* Enable DLAB. */
+  outb (LCR_REG, make_lcr (bits, parity, stop, false, true));
+
+  /* Set baud rate. */
+  outb (LS_REG, divisor & 0xff);
+  outb (MS_REG, divisor >> 8);
+  
+  /* Reset DLAB. */
+  outb (LCR_REG, make_lcr (bits, parity, stop, false, false));
+}
diff --git a/src/devices/timer.c b/src/devices/timer.c
index 4271c73..d23bed3 100644
--- a/src/devices/timer.c
+++ b/src/devices/timer.c
@@ -7,14 +7,10 @@
 #error 8254 timer requires TIMER_FREQ >= 19
 #endif
 
+/* Number of timer ticks since OS booted. */
 static volatile int64_t ticks;
 
-static void
-irq20_timer (struct intr_frame *args UNUSED)
-{
-  ticks++;
-  intr_yield_on_return ();
-}
+static intr_handler_func timer_interrupt;
 
 /* Sets up the 8254 Programmable Interrupt Timer (PIT) to
    interrupt PIT_FREQ times per second, and registers the
@@ -30,9 +26,10 @@ timer_init (void)
   outb (0x40, count & 0xff);
   outb (0x40, count >> 8);
 
-  intr_register (0x20, 0, INTR_OFF, irq20_timer, "8254 Timer");
+  intr_register (0x20, 0, INTR_OFF, timer_interrupt, "8254 Timer");
 }
 
+/* Returns the number of timer ticks since the OS booted. */
 int64_t
 timer_ticks (void) 
 {
@@ -42,13 +39,15 @@ timer_ticks (void)
   return t;
 }
 
+/* Returns the number of timer ticks elapsed since THEN, which
+   should be a value once returned by timer_ticks(). */
 int64_t
 timer_elapsed (int64_t then) 
 {
   return timer_ticks () - then;
 }
 
-/* Suspends execution for approximately DURATION milliseconds. */
+/* Suspends execution for approximately MS milliseconds. */
 void
 timer_msleep (int64_t ms) 
 {
@@ -59,14 +58,26 @@ timer_msleep (int64_t ms)
     continue;
 }
 
+/* Suspends execution for approximately US microseconds.
+   Note: this is ridiculously inaccurate. */
 void
 timer_usleep (int64_t us) 
 {
   timer_msleep (us / 1000 + 1);
 }
 
+/* Suspends execution for approximately NS nanoseconds.
+   Note: this is ridiculously inaccurate. */
 void
 timer_nsleep (int64_t ns) 
 {
   timer_msleep (ns / 1000000 + 1);
 }
+
+/* Timer interrupt handler. */
+static void
+timer_interrupt (struct intr_frame *args UNUSED)
+{
+  ticks++;
+  intr_yield_on_return ();
+}
diff --git a/src/devices/vga.c b/src/devices/vga.c
index 28235af..fdddd91 100644
--- a/src/devices/vga.c
+++ b/src/devices/vga.c
@@ -5,86 +5,128 @@
 #include "lib.h"
 #include "mmu.h"
 
-static size_t vga_cols, vga_rows;
-static size_t vga_x, vga_y;
-static uint16_t *vga_base;
+/* VGA text screen support.  See [FREEVGA] for more information. */
 
-void
-vga_init (void)
-{
-  vga_cols = 80;
-  vga_rows = 25;
-  vga_base = (uint16_t *) ptov (0xb8000);
-  vga_cls ();
-}
+/* Number of columns and rows on the text display. */
+#define COL_CNT 80
+#define ROW_CNT 25
 
-void
-vga_cls (void)
-{
-  size_t i;
-  for (i = 0; i < vga_cols * vga_rows; i++)
-    vga_base[i] = 0x0700;
-  vga_x = vga_y = 0;
-}
+/* Current cursor position.  (0,0) is in the upper left corner of
+   the display. */
+static size_t cx, cy;
 
-static void
-vga_newline (void)
-{
-  vga_x = 0;
-  vga_y++;
-  if (vga_y >= vga_rows)
-    {
-      vga_y = vga_rows - 1;
-      memmove (vga_base, vga_base + vga_cols,
-               vga_cols * (vga_rows - 1) * 2);
-      memset (vga_base + vga_cols * (vga_rows - 1),
-              0, vga_cols * 2);
-    }
-}
+/* Attribute value for gray text on a black background. */
+#define GRAY_ON_BLACK 0x07
 
-static void
-move_cursor (void) 
+/* Framebuffer.  See [FREEVGA] under "VGA Text Mode Operation".
+   The character at (x,y) is fb[y][x][0].
+   The attribute at (x,y) is fb[y][x][1]. */
+static uint8_t (*fb)[COL_CNT][2];
+
+static void clear_row (size_t y);
+static void cls (void);
+static void newline (void);
+static void move_cursor (void);
+
+/* Initializes the VGA text display and clears the screen. */
+void
+vga_init (void)
 {
-  uint16_t cp = (vga_x + vga_cols * vga_y);
-  outw (0x3d4, 0x0e | (cp & 0xff00));
-  outw (0x3d4, 0x0f | (cp << 8));
+  fb = ptov (0xb8000);
+  cls ();
 }
 
+/* Writes C to the VGA text display, interpreting control
+   characters in the conventional ways. */
 void
 vga_putc (int c)
 {
   switch (c) 
     {
     case '\n':
-      vga_newline ();
+      newline ();
       break;
 
     case '\f':
-      vga_cls ();
+      cls ();
       break;
 
     case '\b':
-      if (vga_x > 0)
-        vga_x--;
+      if (cx > 0)
+        cx--;
       break;
       
     case '\r':
-      vga_x = 0;
+      cx = 0;
       break;
 
     case '\t':
-      vga_x = (vga_x + 8) / 8 * 8;
-      if (vga_x >= vga_cols)
-        vga_newline ();
+      cx = ROUND_UP (cx + 1, 8);
+      if (cx >= COL_CNT)
+        newline ();
       break;
       
     default:
-      vga_base[vga_x + vga_y * vga_cols] = 0x0700 | c;
-      vga_x++;
-      if (vga_x >= vga_cols)
-        vga_newline ();
+      fb[cy][cx][0] = c;
+      fb[cy][cx][1] = GRAY_ON_BLACK;
+      if (++cx >= COL_CNT)
+        newline ();
       break;
     }
 
+  /* Update cursor position. */
   move_cursor ();
 }
+
+/* Clears the screen and moves the cursor to the upper left. */
+static void
+cls (void)
+{
+  size_t y;
+
+  for (y = 0; y < ROW_CNT; y++)
+    clear_row (y);
+
+  cx = cy = 0;
+  move_cursor ();
+}
+
+/* Clears row Y to spaces. */
+static void
+clear_row (size_t y) 
+{
+  size_t x;
+
+  for (x = 0; x < COL_CNT; x++)
+    {
+      fb[y][x][0] = ' ';
+      fb[y][x][1] = GRAY_ON_BLACK;
+    }
+}
+
+/* Advances the cursor to the first column in the next line on
+   the screen.  If the cursor is already on the last line on the
+   screen, scrolls the screen upward one line. */
+static void
+newline (void)
+{
+  cx = 0;
+  cy++;
+  if (cy >= ROW_CNT)
+    {
+      cy = ROW_CNT - 1;
+      memmove (&fb[0], &fb[1], sizeof fb[0] * (ROW_CNT - 1));
+      clear_row (ROW_CNT - 1);
+    }
+}
+
+/* Moves the hardware cursor to (cx,cy). */
+static void
+move_cursor (void) 
+{
+  /* See [FREEVGA] under "Manipulating the Text-mode Cursor". */
+  uint16_t cp = cx + COL_CNT * cy;
+  outw (0x3d4, 0x0e | (cp & 0xff00));
+  outw (0x3d4, 0x0f | (cp << 8));
+}
+
diff --git a/src/devices/vga.h b/src/devices/vga.h
index a859dea..2221034 100644
--- a/src/devices/vga.h
+++ b/src/devices/vga.h
@@ -2,7 +2,6 @@
 #define HEADER_VGA_H 1
 
 void vga_init (void);
-void vga_cls (void);
 void vga_putc (int);
 
 #endif /* vga.h */