diff --git a/src/config.c b/src/config.c
index 8aecc61..dbfcb1a 100644
--- a/src/config.c
+++ b/src/config.c
@@ -7,6 +7,7 @@
 #include "scode.h"
 #include "log.h"
 
+/* command line options for UPIWIN */
 static const struct option long_options[] = {
   {"framebuffer", required_argument, 0, 'F'},
   {"help",        no_argument,       0, 'h'},
@@ -16,6 +17,7 @@ static const struct option long_options[] = {
 
 static const char *short_options = "F:hT:";
 
+/* printed to stdout when upiwin is executed with -h/--help option */
 static const char *helptext =
   "UPIWIN - Micro Pi Windows server program\n\n"
   "Usage: upiwin [options] scriptname [scriptargs]\n\n"
@@ -25,19 +27,20 @@ static const char *helptext =
   "  -T,--touchscreen - Specifies the touchscreen device name\n"
   "";
 
-#define EXITFUNCBLOCK_FUNCCOUNT 64
+#define EXITFUNCBLOCK_FUNCCOUNT 64  /* number of exit functions per function block */
 
+/* exit functions are stored in these data blocks */
 typedef struct tagEXITFUNCBLOCK
 {
-  struct tagEXITFUNCBLOCK *next;
-  int num_funcs;
-  PEXITFUNC funcs[EXITFUNCBLOCK_FUNCCOUNT];
+  struct tagEXITFUNCBLOCK *next;             /* chained in single linked list */
+  int num_funcs;                             /* number of functions this block contains */
+  PEXITFUNC funcs[EXITFUNCBLOCK_FUNCCOUNT];  /* pointers to functions */
 } EXITFUNCBLOCK, *PEXITFUNCBLOCK;
 
 /* The global configuration data */
 GLOBAL_CONFIG Gconfig;
 
-static PEXITFUNCBLOCK exitfuncs = NULL;
+static PEXITFUNCBLOCK exitfuncs = NULL;   /* pointer to head of exit function chain */
 
 static void run_exit_funcs(void)
 {
@@ -50,6 +53,7 @@ static void run_exit_funcs(void)
     exitfuncs = p->next;
     for (i = p->num_funcs - 1; i >= 0; i--)
     {
+      /* execute functions in LIFO order */
       ASSERT(p->funcs[i]);
       (*(p->funcs[i]))();
     }
@@ -59,6 +63,7 @@ static void run_exit_funcs(void)
 
 static void init_defaults(void)
 {
+  memset(&Gconfig, 0, sizeof(GLOBAL_CONFIG));
   Gconfig.framebuffer_device = "/dev/fb1";
   Gconfig.touchscreen_device = "/dev/input/touchscreen";
   Gconfig.button_debounce = 100;
@@ -79,7 +84,7 @@ static HRESULT parse_cmdline(int argc, char *argv[], GLOBAL_CONFIG *parsed)
       break;
     switch (c)
     {
-      case 'F':
+      case 'F':   /* frame buffer device name */
 	pstr = strdup(optarg);
 	if (!pstr)
 	{
@@ -91,11 +96,11 @@ static HRESULT parse_cmdline(int argc, char *argv[], GLOBAL_CONFIG *parsed)
 	parsed->framebuffer_device = pstr;
 	break;
 
-      case 'h':
+      case 'h':   /* show help */
 	help = TRUE;
 	break;
 
-      case 'T':
+      case 'T':   /* touchscreen device name */
 	pstr = strdup(optarg);
 	if (!pstr)
 	{
@@ -138,10 +143,16 @@ HRESULT Config_setup(int argc, char *argv[])
     Log(LFATAL, "Unable to set up exit function mechanism");
     return E_FAIL;
   }
+
+  /* set defaults */
   init_defaults();
+
+  /* evaluate command line */
   hr = parse_cmdline(argc, argv, &from_commandline);
   if (hr != S_OK)
     return hr;
+
+  /* command line overrides everything */
   overlay_config(&from_commandline);
   return S_OK;
 }
diff --git a/src/config.h b/src/config.h
index 3955d9c..e543bd4 100644
--- a/src/config.h
+++ b/src/config.h
@@ -5,14 +5,15 @@
 
 typedef void (*PEXITFUNC)(void);
 
+/* global configuration data for UPIWIN */
 typedef struct tagGLOBAL_CONFIG {
-  PCSTR framebuffer_device;
-  PCSTR touchscreen_device;
-  UINT32 button_debounce;
-  UINT32 sys_mq_length;
+  PCSTR framebuffer_device;    /* name of frame buffer device */
+  PCSTR touchscreen_device;    /* name of touchscreen device */
+  UINT32 button_debounce;      /* minimum time between button up and next button down (ms) */
+  UINT32 sys_mq_length;        /* length of system message queue */
 } GLOBAL_CONFIG;
 
-extern GLOBAL_CONFIG Gconfig;
+extern GLOBAL_CONFIG Gconfig;  /* one global configuration to rule them all */
 
 extern HRESULT Config_setup(int argc, char *argv[]);
 extern HRESULT Config_exitfunc(PEXITFUNC pfn);
diff --git a/src/fbinit.c b/src/fbinit.c
index 24cbe7e..11bbcd3 100644
--- a/src/fbinit.c
+++ b/src/fbinit.c
@@ -16,12 +16,13 @@ extern uint8_t _binary_splash_bin_start[];
 extern uint8_t _binary_splash_bin_end;
 extern uint8_t _binary_splash_bin_size;
 
-static int fb_fd = -1;
+static int fb_fd = -1;   /* framebuffer file descriptor */
 
+/* frame buffer information */
 static FBINFO local_info;
 PCFBINFO Fb_Info = &local_info;
 
-UINT16 *Fb_Ptr = NULL;
+UINT16 *Fb_Ptr = NULL;   /* pointer to memory-mapped frame buffer */
 
 inline static UINT16 makemask(unsigned offset, unsigned length)
 {
@@ -30,12 +31,11 @@ inline static UINT16 makemask(unsigned offset, unsigned length)
 
 static void do_cleanup(void)
 {
-  /* additional cleanup here */
-  
+  /* black out the display */
   memset(Fb_Ptr, 0, local_info.screenbytes);
-  munmap((void *)Fb_Ptr, local_info.screenbytes);
-  Fb_Ptr = NULL;
   
+  munmap((void *)Fb_Ptr, local_info.screenbytes);
+  Fb_Ptr = NULL;  
   close(fb_fd);
   fb_fd = -1;
 }
@@ -50,10 +50,11 @@ HRESULT Fb_setup(void)
   if (fb_fd == -1)
   {
     hr = ERRNO_AS_SCODE;
-    Log(LFATAL, "Unable to open framebuffer (%08X)", hr);
+    Log(LFATAL, "Unable to open framebuffer device %s (%08X)", Gconfig.framebuffer_device, hr);
     return hr;
   }
 
+  /* fixed info is needed to get the memory parameters for the display */
   if (ioctl(fb_fd, FBIOGET_FSCREENINFO, &fixed))
   {
     hr = ERRNO_AS_SCODE;
@@ -64,6 +65,7 @@ HRESULT Fb_setup(void)
   local_info.linebytes = fixed.line_length;
   local_info.screenbytes = fixed.smem_len;
 
+  /* variable info is used to get scren geometry and color info */
   if (ioctl(fb_fd, FBIOGET_VSCREENINFO, &var))
   {
     hr = ERRNO_AS_SCODE;
@@ -100,8 +102,6 @@ HRESULT Fb_setup(void)
   /* display the splash screen */
   memcpy(Fb_Ptr, _binary_splash_bin_start, (size_t)(&_binary_splash_bin_size));
 
-  /* additional setup here */
-
   hr = Config_exitfunc(do_cleanup);
   if (FAILED(hr))
     do_cleanup();
diff --git a/src/fbinit.h b/src/fbinit.h
index 8638317..66e4f35 100644
--- a/src/fbinit.h
+++ b/src/fbinit.h
@@ -3,28 +3,29 @@
 
 #include "wintype.h"
 
+/* info about the frame buffer */
 typedef struct tagFBINFO {
-  UINT32 width;
-  UINT32 height;
-  UINT32 virtual_width;
-  UINT32 virtual_height;
-  UINT32 bpp;
-  UINT32 linebytes;
-  UINT32 screenbytes;
-  UINT16 red_offset;
-  UINT16 red_length;
-  UINT16 red_mask;
-  UINT16 green_offset;
-  UINT16 green_length;
-  UINT16 green_mask;
-  UINT16 blue_offset;
-  UINT16 blue_length;
-  UINT16 blue_mask;
+  UINT32 width;               /* screen width */
+  UINT32 height;              /* screen height */
+  UINT32 virtual_width;       /* virtual screen width */
+  UINT32 virtual_height;      /* virtual screen height */
+  UINT32 bpp;                 /* bits per pixel (16) */
+  UINT32 linebytes;           /* number of bytes per line */
+  UINT32 screenbytes;         /* number of bytes for the entire screen */
+  UINT16 red_offset;          /* offset of "red" bits within pixel word (11) */
+  UINT16 red_length;          /* number of "red" bits within pixel word (5) */
+  UINT16 red_mask;            /* mask for the "red" bits in a pixel word */
+  UINT16 green_offset;        /* offset of "green" bits within pixel word (5) */
+  UINT16 green_length;        /* number of "green" bits within pixel word (6) */
+  UINT16 green_mask;          /* mask for the "green" bits in a pixel word */
+  UINT16 blue_offset;         /* offset of "blue" bits within pixel word (0) */
+  UINT16 blue_length;         /* number of "blue" bits within pixel word (5) */
+  UINT16 blue_mask;           /* mask for the "blue" bits in a pixel word */
 } FBINFO;
 typedef const FBINFO * const PCFBINFO;
 
-extern PCFBINFO Fb_Info;
-extern UINT16 *Fb_Ptr;
+extern PCFBINFO Fb_Info;     /* pointer to screen information */
+extern UINT16 *Fb_Ptr;       /* pointer to memory-mapped screen buffer */
 
 extern HRESULT Fb_setup(void);
 extern void Fb_clear(void);
diff --git a/src/fbprimitive.c b/src/fbprimitive.c
index 805dcd4..f434226 100644
--- a/src/fbprimitive.c
+++ b/src/fbprimitive.c
@@ -25,6 +25,7 @@ void Fb_line(INT32 x1, INT32 y1, INT32 x2, INT32 y2, UINT16 color, BOOL xor)
   INT32 dx = x2 - x1;
   INT32 dy = y2 - y1;
 
+  /* uses Bresenham's line algorithm with fixed-point arithmetic */
   if (ABS(dx) < ABS(dy))
   {
     if (y1 > y2)
diff --git a/src/fbprimitive.h b/src/fbprimitive.h
index fddd6c8..8f0ea8e 100644
--- a/src/fbprimitive.h
+++ b/src/fbprimitive.h
@@ -3,6 +3,7 @@
 
 #include "wintype.h"
 
+/* Some predefined "primitive" color values */
 #define FBPRIMCLR_BLACK   0x0000
 #define FBPRIMCLR_RED     0xF800
 #define FBPRIMCLR_GREEN   0x07E0
diff --git a/src/gpio.c b/src/gpio.c
index b4e8758..dfe0710 100644
--- a/src/gpio.c
+++ b/src/gpio.c
@@ -5,13 +5,14 @@
 #include "scode.h"
 #include "gpio.h"
 
+/* GPIO lines used by various peripheral devices */
 #define GLINE_BUTTON1   17
 #define GLINE_BUTTON2   22
 #define GLINE_BUTTON3   23
 #define GLINE_BUTTON4   27
 #define GLINE_BACKLIGHT 18
 
-#define PWM_BACKLIGHT   0
+#define PWM_BACKLIGHT   0   /* PWM channel used for backlight */
 
 static void do_cleanup(void)
 {
diff --git a/src/gpio.h b/src/gpio.h
index 24c7398..707393a 100644
--- a/src/gpio.h
+++ b/src/gpio.h
@@ -3,14 +3,15 @@
 
 #include "wintype.h"
 
-#define GPIO_BUTTON_COUNT  4
+#define GPIO_BUTTON_COUNT  4           /* number of GPIO buttons we have */
 
+/* state flags for the GPIO buttons */
 #define GRB_STATE_BUTTON1  (1 << 0)
 #define GRB_STATE_BUTTON2  (1 << 1)
 #define GRB_STATE_BUTTON3  (1 << 2)
 #define GRB_STATE_BUTTON4  (1 << 3)
 
-#define GSB_BACKLIGHT_MAX   1023
+#define GSB_BACKLIGHT_MAX   1023       /* maximum level for backlight */
 
 extern HRESULT Gpio_setup(void);
 extern UINT32 Gpio_read_buttons(void);
diff --git a/src/log.c b/src/log.c
index 81afc30..e6ab3c6 100644
--- a/src/log.c
+++ b/src/log.c
@@ -4,8 +4,11 @@
 #include <sys/time.h>
 #include "log.h"
 
+/* string equivalents to the severity values */
 static const char *severities[] = { "FATAL", "ERROR", "WARN ", "INFO ", "DEBUG" };
 
+static FILE *logfile = stdout;  /* log file pointer */
+
 void Log(int level, const char *format, ...)
 {
   va_list argp;
@@ -21,7 +24,7 @@ void Log(int level, const char *format, ...)
   gettimeofday(&tv, NULL);
   localtime_r(&(tv.tv_sec), &tm);
   strftime(timestamp, 32, "%F %T", &tm);
-  printf("%s.%06u %s %s\n", timestamp, tv.tv_usec, severities[level], buf);
+  fprintf(logfile, "%s.%06u %s %s\n", timestamp, tv.tv_usec, severities[level], buf);
 }
 
 void Log_assert_failed(const char *test, const char *file, int line)
diff --git a/src/log.h b/src/log.h
index 82145f5..a0871ca 100644
--- a/src/log.h
+++ b/src/log.h
@@ -1,18 +1,21 @@
 #ifndef __LOG_H_INCLUDED
 #define __LOG_H_INCLUDED
 
-#define LFATAL 0
-#define LERROR 1
-#define LWARN  2
-#define LINFO  3
-#define LDEBUG 4
+/* Logging level severities */
+#define LFATAL 0    /* fatal error */
+#define LERROR 1    /* error */
+#define LWARN  2    /* warning */
+#define LINFO  3    /* information */
+#define LDEBUG 4    /* debugging */
 
 extern void Log(int level, const char *format, ...);
 extern void Log_assert_failed(const char *test, const char *file, int line);
 
+/* Current file name definitions for assert macros */
 #define THIS_FILE __FILE__
 #define DECLARE_THIS_FILE() static const char THIS_FILE[] = __FILE__
 
+/* Assert macros */
 #ifdef DEBUG_ASSERT
 #define ASSERT(x)  ((x) ? (void)0 : Log_assert_failed(#x, THIS_FILE, __LINE__))
 #define VERIFY(x)  ASSERT(x)
diff --git a/src/main.c b/src/main.c
index 459ae84..7bdd267 100644
--- a/src/main.c
+++ b/src/main.c
@@ -35,6 +35,7 @@ int main(int argc, char *argv[])
   MSG msg;
   char *tmp;
 
+  /* initialization sequence */
   Time_init();
   hr = Config_setup(argc, argv);
   if (FAILED(hr))
@@ -48,7 +49,7 @@ int main(int argc, char *argv[])
   if (FAILED(Sys_enable_input()))
     return EXIT_FAILURE;
   Log(LINFO, "Pausing at startup.");
-  sleep(5); /* wait to show off splash screen */
+  sleep(3); /* wait to show off splash screen */
 
   Fb_clear();
   /* temporary drawing here */
diff --git a/src/msg_queue.h b/src/msg_queue.h
index 1ba3626..10c49ae 100644
--- a/src/msg_queue.h
+++ b/src/msg_queue.h
@@ -1,22 +1,25 @@
 #ifndef __MSG_QUEUE_H_INCLUDED
 #define __MSG_QUEUE_H_INCLUDED
 
+#include <pthread.h>
 #include "wintype.h"
 #include "msg.h"
 
+/* internal structure of a message queue */
 typedef struct tagMSG_QUEUE {
-  struct tagMSG_QUEUE *next;
-  PMSG startbound;
-  PMSG endbound;
-  PMSG head;
-  PMSG tail;
-  UINT32 nentries;
-  pthread_mutex_t mutex;
-  MSG messagestore[0];
+  struct tagMSG_QUEUE *next;    /* allow us to be in a singly-linked list */
+  PMSG startbound;              /* start boundary for message buffer */
+  PMSG endbound;                /* end boundary for message buffer */
+  PMSG head;                    /* head pointer of message queue */
+  PMSG tail;                    /* tail pointer of message queue */
+  UINT32 nentries;              /* number of entries possible in message buffer */
+  pthread_mutex_t mutex;        /* controls access to queue from multiple threads */
+  MSG messagestore[0];          /* message buffer */
 } MSG_QUEUE, *PMSG_QUEUE;
 
-#define PEEK_REMOVE   0x0001
-#define PEEK_NOREMOVE 0x0000
+/* flags to Mq_peek */
+#define PEEK_REMOVE   0x0001    /* remove message if found */
+#define PEEK_NOREMOVE 0x0000    /* do not remove message if found */
 
 extern PMSG_QUEUE Mq_alloc(UINT32 nentries);
 extern void Mq_destroy(PMSG_QUEUE queue);
diff --git a/src/sysinput.c b/src/sysinput.c
index dcec699..530489c 100644
--- a/src/sysinput.c
+++ b/src/sysinput.c
@@ -13,20 +13,22 @@
 #include "gpio.h"
 #include "time_func.h"
 
-#define INPUT_EVENT_BATCH 16
+#define INPUT_EVENT_BATCH 16   /* number of events to retrieve from touchscreen at once */
 
-PMSG_QUEUE Sys_Queue = NULL;
+PMSG_QUEUE Sys_Queue = NULL;   /* system message queue */
+static int ts_fd = 0;          /* file descriptor for touchscreen */
 
-static pthread_t ithread;
-static volatile sig_atomic_t running = 1;
-static int ts_fd = 0;
+static pthread_t ithread;                    /* input thread handle */
+static volatile sig_atomic_t running = 1;    /* "running" flag for input thread */
 
-static UINT32 last_bstate = 0;
-static TIMESTAMP button_event_ok[GPIO_BUTTON_COUNT];
+/* Local data for poll_buttons() */
+static UINT32 last_bstate = 0;                        /* previous button state */
+static TIMESTAMP button_event_ok[GPIO_BUTTON_COUNT];  /* timestamps to debounce events */
 
-static UINT_PTR touch_x = 0;
-static UINT_PTR touch_y = 0;
-static UINT32 touch_nextmsg = WM_TOUCHMOVE;
+/* Local data for poll_touchscreen() */
+static UINT_PTR touch_x = 0;                  /* X coordinate to send with next message */
+static UINT_PTR touch_y = 0;                  /* Y coordinate to send with next message */
+static UINT32 touch_nextmsg = WM_TOUCHMOVE;   /* identifier of next message to send */
 
 static void poll_buttons(void)
 {
@@ -44,9 +46,10 @@ static void poll_buttons(void)
     for (attr = 1, mask = GRB_STATE_BUTTON1; attr <= GPIO_BUTTON_COUNT; attr++, mask <<= 1)
     {
       if (now < button_event_ok[attr - 1])
-	continue;
+	continue;  /* this is a "contact bounce" event, don't bother */
       if (up & mask)
       {
+	/* reset contact bounce timer - only seems to happen after button releases */
 	button_event_ok[attr - 1] = now + Gconfig.button_debounce;
 	Mq_post1(Sys_Queue, 0, WM_HWBUTTONUP, attr);
       }
@@ -75,10 +78,12 @@ static void poll_touchscreen(void)
     Log(LERROR, "Unexpected end of file reading from touchscreen device");
     return;
   }
+  
   nev = nb / sizeof(struct input_event);
   xerrno = nev * sizeof(struct input_event);
   if (nb > xerrno)
     Log(LERROR, "read %d bytes from touchscreen but we can only use %d", nb, xerrno);
+  
   for (i=0; i<nev; i++)
   {
     switch (buffer[i].type)
@@ -111,6 +116,7 @@ static void poll_touchscreen(void)
 
 static void *input_thread(void *arg)
 {
+  /* clear all state at startup */
   last_bstate = 0;
   memset(button_event_ok, 0, GPIO_BUTTON_COUNT * sizeof(TIMESTAMP));
   touch_x = touch_y = 0;
@@ -151,7 +157,7 @@ HRESULT Sys_enable_input(void)
   {
     rc = ERRNO_AS_SCODE;
     Mq_destroy(Sys_Queue);
-    Log(LFATAL, "Unable to open touchscreen device (%08X).", rc);
+    Log(LFATAL, "Unable to open touchscreen device %s (%08X).", Gconfig.touchscreen_device, rc);
     return rc;
   }
   
diff --git a/src/time_func.c b/src/time_func.c
index 8bdda09..f7603ff 100644
--- a/src/time_func.c
+++ b/src/time_func.c
@@ -2,7 +2,7 @@
 #include <sys/time.h>
 #include "time_func.h"
 
-static TIMESTAMP start_timestamp = 0;
+static TIMESTAMP start_timestamp = 0;  /* time since epoch at start of run */
 
 TIMESTAMP Time_since_epoch(void)
 {
diff --git a/src/wintype.h b/src/wintype.h
index 96c3645..34bdf50 100644
--- a/src/wintype.h
+++ b/src/wintype.h
@@ -32,7 +32,7 @@
 #define INT64_BITS  64
 #define UINT64_BITS 64
 
-#define LOG_PTRSIZE 2    /* log2(sizeof(void *)) */
+#define LOG_PTRSIZE     2   /* log2(sizeof(void *)) */
 
 #define LOG_INTSIZE     2   /* log2(sizeof(int)) */
 #define LOG_UINTSIZE    2   /* log2(sizeof(UINT32)) */