Update usb userland stuff to reflect hid changes in the kernel.

This adds the new program usbhidaction which can be used to assign actions
to events that occur on a uhid device.  For example, you can now make the
volume buttons on some newer keyboards actually do something.

2 files changed, 393 insertions, 153 deletions

diff --git a/usr.bin/usbhidctl/usbhid.c b/usr.bin/usbhidctl/usbhid.c
index 1751eb8d1ea..83dd7f7abf7 100644
--- a/usr.bin/usbhidctl/usbhid.c
+++ b/usr.bin/usbhidctl/usbhid.c
@@ -1,8 +1,8 @@
-/*	$OpenBSD: usbhid.c,v 1.3 2002/05/02 20:12:07 nate Exp $	*/
-/*      $NetBSD: usbhid.c,v 1.17 2001/03/28 03:17:42 simonb Exp $ */
+/*	$OpenBSD: usbhid.c,v 1.4 2002/05/10 00:09:17 nate Exp $	*/
+/*      $NetBSD: usbhid.c,v 1.22 2002/02/20 20:30:42 christos Exp $ */
 
 /*
- * Copyright (c) 2000 The NetBSD Foundation, Inc.
+ * Copyright (c) 2001 The NetBSD Foundation, Inc.
  * All rights reserved.
  *
  * This code is derived from software contributed to The NetBSD Foundation
@@ -53,14 +53,18 @@
 #include <unistd.h>
 #include <usbhid.h>
 
+/*
+ * Zero if not in a verbose mode.  Greater levels of verbosity
+ * are indicated by values larger than one.
+ */
+unsigned int verbose;
+
 /* Parser tokens */
 #define DELIM_USAGE '.'
 #define DELIM_PAGE ':'
 #define DELIM_SET '='
 
-/* Zero if not in a verbose mode.  Greater levels of verbosity are
-   indicated by values larger than one. */
-static unsigned int verbose;
+static int reportid;
 
 struct Susbvar {
 	/* Variable name, not NUL terminated */
@@ -77,6 +81,7 @@ struct Susbvar {
 #define MATCH_SHOWPAGENAME	(1 << 5)
 #define MATCH_SHOWNUMERIC	(1 << 6)
 #define MATCH_WRITABLE		(1 << 7)
+#define MATCH_SHOWVALUES	(1 << 8)
 	unsigned int mflags;
 
 	/* Workspace for hidmatch() */
@@ -108,11 +113,183 @@ static struct {
 #define REPORT_MAXVAL 2
 };
 
+/*
+ * Extract 16-bit unsigned usage ID from a numeric string.  Returns -1
+ * if string failed to parse correctly.
+ */
+static int
+strtousage(const char *nptr, size_t nlen)
+{
+	char *endptr;
+	long result;
+	char numstr[16];
+
+	if (nlen >= sizeof(numstr) || !isdigit((unsigned char)*nptr))
+		return -1;
+
+	/*
+	 * We use strtol() here, but unfortunately strtol() requires a
+	 * NUL terminated string - which we don't have - at least not
+	 * officially.
+	 */
+	memcpy(numstr, nptr, nlen);
+	numstr[nlen] = '\0';
+
+	result = strtol(numstr, &endptr, 0);
+
+	if (result < 0 || result > 0xffff || endptr != &numstr[nlen])
+		return -1;
+
+	return result;
+}
+
+struct usagedata {
+	char const *page_name;
+	char const *usage_name;
+	size_t page_len;
+	size_t usage_len;
+	int isfinal;
+	u_int32_t usage_id;
+};
+
+/*
+ * Test a rule against the current usage data.  Returns -1 on no
+ * match, 0 on partial match and 1 on complete match.
+ */
+static int
+hidtestrule(struct Susbvar *var, struct usagedata *cache)
+{
+	char const *varname;
+	ssize_t matchindex, pagesplit;
+	size_t strind, varlen;
+	int numusage;
+	u_int32_t usage_id;
+
+	matchindex = var->matchindex;
+	varname = var->variable;
+	varlen = var->varlen;
+
+	usage_id = cache->usage_id;
+
+	/*
+	 * Parse the current variable name, locating the end of the
+	 * current 'usage', and possibly where the usage page name
+	 * ends.
+	 */
+	pagesplit = -1;
+	for (strind = matchindex; strind < varlen; strind++) {
+		if (varname[strind] == DELIM_USAGE)
+			break;
+		if (varname[strind] == DELIM_PAGE)
+			pagesplit = strind;
+	}
+
+	if (cache->isfinal && strind != varlen)
+		/*
+		 * Variable name is too long (hit delimiter instead of
+		 * end-of-variable).
+		 */
+		return -1;
+
+	if (pagesplit >= 0) {
+		/*
+		 * Page name was specified, determine whether it was
+		 * symbolic or numeric.  
+		 */
+		char const *strstart;
+		int numpage;
+
+		strstart = &varname[matchindex];
+
+		numpage = strtousage(strstart, pagesplit - matchindex);
+
+		if (numpage >= 0) {
+			/* Valid numeric */
+
+			if (numpage != HID_PAGE(usage_id))
+				/* Numeric didn't match page ID */
+				return -1;
+		} else {
+			/* Not a valid numeric */
+
+			/*
+			 * Load and cache the page name if and only if
+			 * it hasn't already been loaded (it's a
+			 * fairly expensive operation).
+			 */
+			if (cache->page_name == NULL) {
+				cache->page_name = hid_usage_page(HID_PAGE(usage_id));
+				cache->page_len = strlen(cache->page_name);
+			}
+
+			/*
+			 * Compare specified page name to actual page
+			 * name.
+			 */
+			if (cache->page_len !=
+			    (size_t)(pagesplit - matchindex) ||
+			    memcmp(cache->page_name,
+				   &varname[matchindex],
+				   cache->page_len) != 0)
+				/* Mismatch, page name wrong */
+				return -1;
+		}
+
+		/* Page matches, discard page name */
+		matchindex = pagesplit + 1;
+	}
+
+	numusage = strtousage(&varname[matchindex], strind - matchindex);
+
+	if (numusage >= 0) {
+		/* Valid numeric */
+
+		if (numusage != HID_USAGE(usage_id))
+			/* Numeric didn't match usage ID */
+			return -1;
+	} else {
+		/* Not a valid numeric */
+
+		/* Load and cache the usage name */
+		if (cache->usage_name == NULL) {
+			cache->usage_name = hid_usage_in_page(usage_id);
+			cache->usage_len = strlen(cache->usage_name);
+		}
+
+		/*
+		 * Compare specified usage name to actual usage name
+		 */
+		if (cache->usage_len != (size_t)(strind - matchindex) ||
+		    memcmp(cache->usage_name, &varname[matchindex],
+			   cache->usage_len) != 0)
+			/* Mismatch, usage name wrong */
+			return -1;
+	}
+
+	if (cache->isfinal)
+		/* Match */
+		return 1;
+
+	/*
+	 * Partial match: Move index past this usage string +
+	 * delimiter
+	 */
+	var->matchindex = strind + 1;
+
+	return 0;
+}
+
+/*
+ * hidmatch() determines whether the item specified in 'item', and
+ * nested within a heirarchy of collections specified in 'collist'
+ * matches any of the rules in the list 'varlist'.  Returns the
+ * matching rule on success, or NULL on no match.
+ */
 static struct Susbvar*
 hidmatch(u_int32_t const *collist, size_t collen, struct hid_item *item,
 	 struct Susbvar *varlist, size_t vlsize)
 {
-	size_t vlind, colind, vlactive;
+	size_t colind, vlactive, vlind;
 	int iscollection;
 
 	/*
@@ -161,96 +338,52 @@ hidmatch(u_int32_t const *collist, size_t collen, struct hid_item *item,
 		}
 	}
 
+	/*
+	 * Loop through each usage in the collection list, including
+	 * the 'item' itself on the final iteration.  For each usage,
+	 * test which variables named in the rule list are still
+	 * applicable - if any.
+	 */
 	for (colind = 0; vlactive > 0 && colind <= collen; colind++) {
-		char const *usage_name, *page_name;
-		size_t usage_len, page_len;
-		int final;
-		u_int32_t usage_id;
-
-		final = (colind == collen);
+		struct usagedata cache;
 
-		if (final)
-			usage_id = item->usage;
+		cache.isfinal = (colind == collen);
+		if (cache.isfinal)
+			cache.usage_id = item->usage;
 		else
-			usage_id = collist[colind];
+			cache.usage_id = collist[colind];
 
-		usage_name = hid_usage_in_page(usage_id);
-		usage_len = strlen(usage_name);
-
-		page_name = NULL;
+		cache.usage_name = NULL;
+		cache.page_name = NULL;
 
+		/*
+		 * Loop through each rule, testing whether the rule is
+		 * still applicable or not.  For each rule,
+		 * 'matchindex' retains the current match state as an
+		 * index into the variable name string, or -1 if this
+		 * rule has been proven not to match.
+		 */
 		for (vlind = 0; vlind < vlsize; vlind++) {
-			ssize_t matchindex, pagesplit;
-			size_t varlen, strind;
-			char const *varname;
 			struct Susbvar *var;
+			int matchres;
 
 			var = &varlist[vlind];
 
-			matchindex = var->matchindex;
-			varname = var->variable;
-			varlen = var->varlen;
-
-			if (matchindex < 0)
+			if (var->matchindex < 0)
 				/* Mismatch at a previous level */
 				continue;
 
-			pagesplit = -1;
-			for (strind = matchindex; strind < varlen; strind++) {
-				if (varname[strind] == DELIM_USAGE)
-					break;
-				if (varname[strind] == DELIM_PAGE)
-					pagesplit = strind;
-			}
+			matchres = hidtestrule(var, &cache);
 
-			if (final && strind != varlen) {
-				/*
-				 * Variable name is too long (hit
-				 * delimiter instead of
-				 * end-of-variable)
-				 */
-				var->matchindex = -1;
-				vlactive--;
-				continue;
-			}
-
-			if (pagesplit >= 0) {
-				if (page_name == NULL) {
-					page_name = hid_usage_page(HID_PAGE(usage_id));
-					page_len = strlen(page_name);
-				}
-				if (page_len !=
-				    (size_t)(pagesplit - matchindex) ||
-				    memcmp(page_name, &varname[matchindex],
-					   page_len) != 0) {
-					/* Mismatch, page name wrong */
-					var->matchindex = -1;
-					vlactive--;
-					continue;
-				}
-
-				/* Page matches, discard page name */
-				matchindex = pagesplit + 1;
-			}
-
-			if (usage_len != strind - matchindex ||
-			    memcmp(usage_name, &varname[matchindex],
-				   usage_len) != 0) {
-				/* Mismatch, usage name wrong */
+			if (matchres < 0) {
+				/* Bad match */
 				var->matchindex = -1;
 				vlactive--;
 				continue;
-			}
-
-			if (final)
-				/* Match */
+			} else if (matchres > 0) {
+				/* Complete match */
 				return var;
-
-			/*
-			 * Partial match: Move index past this usage
-			 * string + delimiter
-			 */
-			var->matchindex = matchindex + usage_len + 1;
+			}
 		}
 	}
 
@@ -262,8 +395,7 @@ allocreport(struct Sreport *report, report_desc_t rd, int repindex)
 {
 	int reptsize;
 
-	reptsize = hid_report_size(rd, reptoparam[repindex].hid_kind,
-				   &report->report_id);
+	reptsize = hid_report_size(rd, reptoparam[repindex].hid_kind, reportid);
 	if (reptsize < 0)
 		errx(1, "Negative report size");
 	report->size = reptsize;
@@ -302,7 +434,8 @@ getreport(struct Sreport *report, int hidfd, report_desc_t rd, int repindex)
 
 		report->buffer->ucr_report = reptoparam[repindex].uhid_report;
 		if (ioctl(hidfd, USB_GET_REPORT, report->buffer) < 0)
-			err(1, "USB_GET_REPORT");
+			err(1, "USB_GET_REPORT (probably not supported by "
+			    "device)");
 	}
 }
 
@@ -335,19 +468,30 @@ varop_display(struct hid_item *item, struct Susbvar *var,
 	      u_int32_t const *collist, size_t collen, u_char *buf)
 {
 	size_t colitem;
-
-	for (colitem = 0; colitem < collen; colitem++) {
+	int val, i;
+
+	for (i = 0; i < item->report_count; i++) {
+		for (colitem = 0; colitem < collen; colitem++) {
+			if (var->mflags & MATCH_SHOWPAGENAME)
+				printf("%s:",
+				    hid_usage_page(HID_PAGE(collist[colitem])));
+			printf("%s.", hid_usage_in_page(collist[colitem]));
+		}
 		if (var->mflags & MATCH_SHOWPAGENAME)
-			printf("%s:",
-			       hid_usage_page(HID_PAGE(collist[colitem])));
-		printf("%s.", hid_usage_in_page(collist[colitem]));
+			printf("%s:", hid_usage_page(HID_PAGE(item->usage)));
+		val = hid_get_data(buf, item);
+		item->pos += item->report_size;
+		if (item->usage_minimum != 0 || item->usage_maximum != 0) {
+			val += item->usage_minimum;
+			printf("%s=1", hid_usage_in_page(val));
+		} else {
+			printf("%s=%d%s", hid_usage_in_page(item->usage),
+			       val, item->flags & HIO_CONST ? " (const)" : "");
+		}
+		if (item->report_count > 1)
+			printf(" [%d]", i);
+		printf("\n");
 	}
-
-	if (var->mflags & MATCH_SHOWPAGENAME)
-		printf("%s:", hid_usage_page(HID_PAGE(item->usage)));
-	printf("%s=%d%s\n", hid_usage_in_page(item->usage),
-	       hid_get_data(buf, item),
-	       (item->flags & HIO_CONST) ? " (const)" : "");
 	return 0;
 }
 
@@ -362,12 +506,8 @@ varop_modify(struct hid_item *item, struct Susbvar *var,
 
 	hid_set_data(buf, item, dataval);
 
-	if (verbose >= 1)
-		/*
-		 * Allow displaying of set value in verbose mode.
-		 * This isn't particularly useful though, so don't
-		 * bother documenting it.
-		 */
+	if (var->mflags & MATCH_SHOWVALUES)
+		/* Display set value */
 		varop_display(item, var, collist, collen, buf);
 
 	return 1;
@@ -376,14 +516,28 @@ varop_modify(struct hid_item *item, struct Susbvar *var,
 static void
 reportitem(char const *label, struct hid_item const *item, unsigned int mflags)
 {
-	printf("%s size=%d count=%d page=%s usage=%s%s", label,
+	int isconst = item->flags & HIO_CONST,
+	    isvar = item->flags & HIO_VARIABLE;
+	printf("%s size=%d count=%d%s%s page=%s", label,
 	       item->report_size, item->report_count,
-	       hid_usage_page(HID_PAGE(item->usage)),
-	       hid_usage_in_page(item->usage),
-	       item->flags & HIO_CONST ? " Const" : "");
-	if (mflags & MATCH_SHOWNUMERIC)
-		printf(" (%u/0x%x)",
-		       HID_PAGE(item->usage), HID_USAGE(item->usage));
+	       isconst ? " Const" : "",
+	       !isvar && !isconst ? " Array" : "",
+	       hid_usage_page(HID_PAGE(item->usage)));
+	if (item->usage_minimum != 0 || item->usage_maximum != 0) {
+		printf(" usage=%s..%s", hid_usage_in_page(item->usage_minimum),
+		       hid_usage_in_page(item->usage_maximum));
+		if (mflags & MATCH_SHOWNUMERIC)
+			printf(" (%u:0x%x..%u:0x%x)",
+			       HID_PAGE(item->usage_minimum),
+			       HID_USAGE(item->usage_minimum),
+			       HID_PAGE(item->usage_maximum),
+			       HID_USAGE(item->usage_maximum));
+	} else {
+		printf(" usage=%s", hid_usage_in_page(item->usage));
+		if (mflags & MATCH_SHOWNUMERIC)
+			printf(" (%u:0x%x)",
+			       HID_PAGE(item->usage), HID_USAGE(item->usage));
+	}
 	printf(", logical range %d..%d",
 	       item->logical_minimum, item->logical_maximum);
 	if (item->physical_minimum != item->physical_maximum)
@@ -402,9 +556,14 @@ varop_report(struct hid_item *item, struct Susbvar *var,
 {
 	switch (item->kind) {
 	case hid_collection:
-		printf("Collection page=%s usage=%s\n",
+		printf("Collection page=%s usage=%s",
 		       hid_usage_page(HID_PAGE(item->usage)),
 		       hid_usage_in_page(item->usage));
+		if (var->mflags & MATCH_SHOWNUMERIC)
+			printf(" (%u:0x%x)\n",
+			       HID_PAGE(item->usage), HID_USAGE(item->usage));
+		else
+			printf("\n");
 		break;
 	case hid_endcollection:
 		printf("End collection\n");
@@ -426,13 +585,12 @@ varop_report(struct hid_item *item, struct Susbvar *var,
 static void
 devloop(int hidfd, report_desc_t rd, struct Susbvar *varlist, size_t vlsize)
 {
+	u_char *dbuf;
 	struct hid_data *hdata;
+	size_t collind, dlen;
 	struct hid_item hitem;
 	u_int32_t colls[128];
 	struct Sreport inreport;
-	size_t dlen;
-	u_char *dbuf;
-	size_t collind;
 
 	allocreport(&inreport, rd, REPORT_INPUT);
 
@@ -446,12 +604,14 @@ devloop(int hidfd, report_desc_t rd, struct Susbvar *varlist, size_t vlsize)
 		ssize_t readlen;
 
 		readlen = read(hidfd, dbuf, dlen);
-		if (readlen < 0 || dlen != (size_t)readlen)
-			err(1, "bad read %ld != %ld",
-			    (long)readlen, (long)dlen);
+		if (readlen < 0)
+			err(1, "Device read error");
+		if (dlen != (size_t)readlen)
+			errx(1, "Unexpected response length: %lu != %lu",
+			     (unsigned long)readlen, (unsigned long)dlen);
 
 		collind = 0;
-		hdata = hid_start_parse(rd, 1 << hid_input);
+		hdata = hid_start_parse(rd, 1 << hid_input, reportid);
 		if (hdata == NULL)
 			errx(1, "Failed to start parser");
 
@@ -476,6 +636,9 @@ devloop(int hidfd, report_desc_t rd, struct Susbvar *varlist, size_t vlsize)
 				errx(1, "Unexpected non-input item returned");
 			}
 
+			if (reportid != -1 && hitem.report_ID != reportid)
+				continue;
+
 			matchvar = hidmatch(colls, collind, &hitem,
 					    varlist, vlsize);
 
@@ -495,10 +658,9 @@ devshow(int hidfd, report_desc_t rd, struct Susbvar *varlist, size_t vlsize,
 	int kindset)
 {
 	struct hid_data *hdata;
+	size_t collind, repind, vlind;
 	struct hid_item hitem;
 	u_int32_t colls[128];
-	size_t collind, repind, vlind;
-
 	struct Sreport reports[REPORT_MAXVAL + 1];
 
 
@@ -509,9 +671,7 @@ devshow(int hidfd, report_desc_t rd, struct Susbvar *varlist, size_t vlsize,
 	}
 
 	collind = 0;
-	hdata = hid_start_parse(rd, kindset |
-				(1 << hid_collection) |
-				(1 << hid_endcollection));
+	hdata = hid_start_parse(rd, kindset, reportid);
 	if (hdata == NULL)
 		errx(1, "Failed to start parser");
 
@@ -519,6 +679,9 @@ devshow(int hidfd, report_desc_t rd, struct Susbvar *varlist, size_t vlsize,
 		struct Susbvar *matchvar;
 		int repindex;
 
+		if (verbose > 3)
+			printf("item: kind=%d repid=%d usage=0x%x\n",
+			       hitem.kind, hitem.report_ID, hitem.usage);
 		repindex = -1;
 		switch (hitem.kind) {
 		case hid_collection:
@@ -542,6 +705,9 @@ devshow(int hidfd, report_desc_t rd, struct Susbvar *varlist, size_t vlsize,
 			break;
 		}
 
+		if (reportid != -1 && hitem.report_ID != reportid)
+			continue;
+
 		matchvar = hidmatch(colls, collind, &hitem, varlist, vlsize);
 
 		if (matchvar != NULL) {
@@ -609,13 +775,13 @@ usage(void)
 int
 main(int argc, char **argv)
 {
-	int hidfd;
-	report_desc_t repdesc;
-	char devnamebuf[PATH_MAX];
 	char const *dev;
-	int ch, wflag, aflag, nflag, rflag, lflag;
-	size_t varnum;
 	char const *table;
+	size_t varnum;
+	int aflag, lflag, nflag, rflag, wflag;
+	int ch, hidfd;
+	report_desc_t repdesc;
+	char devnamebuf[PATH_MAX];
 	struct Susbvar variables[128];
 
 	wflag = aflag = nflag = verbose = rflag = lflag = 0;
@@ -698,6 +864,14 @@ main(int argc, char **argv)
 			if (!wflag)
 				errx(2, "Must specify -w to set variables");
 			svar->mflags |= MATCH_WRITABLE;
+			if (verbose >= 1)
+				/*
+				 * Allow displaying of set value in
+				 * verbose mode.  This isn't
+				 * particularly useful though, so
+				 * don't bother documenting it.
+				 */
+				svar->mflags |= MATCH_SHOWVALUES;
 			svar->varlen = valuesep - name;
 			svar->value = valuesep + 1;
 			svar->opfunc = varop_modify;
@@ -770,6 +944,10 @@ main(int argc, char **argv)
 	if (hidfd < 0)
 		err(1, "%s", dev);
 
+	if (ioctl(hidfd, USB_GET_REPORT_ID, &reportid) < 0)
+		reportid = -1;
+	if (verbose > 1)
+		printf("report ID=%d\n", reportid);
 	repdesc = hid_get_report_desc(hidfd);
 	if (repdesc == 0)
 		errx(1, "USB_GET_REPORT_DESC");
@@ -788,31 +966,18 @@ main(int argc, char **argv)
 		1 << hid_output |
 		1 << hid_feature);
 
-#if 0
-	{
-		size_t repindex;
-		for (repindex = 0;
-		     repindex < (sizeof(reptoparam) / sizeof(*reptoparam));
-		     repindex++)
-			devshow(hidfd, repdesc, variables, varnum,
-				1 << reptoparam[repindex].hid_kind);
-	}
-#endif
-
 	if (rflag) {
 		/* Report mode trailer */
 		size_t repindex;
 		for (repindex = 0;
 		     repindex < (sizeof(reptoparam) / sizeof(*reptoparam));
 		     repindex++) {
-			int report_id, size;
+			int size;
 			size = hid_report_size(repdesc,
 					       reptoparam[repindex].hid_kind,
-					       &report_id);
-			size -= report_id != 0;
-			printf("Total %7s size %s%d bytes\n",
-			       reptoparam[repindex].name,
-			       report_id && size ? "1+" : "", size);
+					       reportid);
+			printf("Total %7s size %d bytes\n",
+			       reptoparam[repindex].name, size);
 		}
 	}
 
diff --git a/usr.bin/usbhidctl/usbhidctl.1 b/usr.bin/usbhidctl/usbhidctl.1
index b7b2ec48efa..87f92e51a1a 100644
--- a/usr.bin/usbhidctl/usbhidctl.1
+++ b/usr.bin/usbhidctl/usbhidctl.1
@@ -1,7 +1,7 @@
-.\" $OpenBSD: usbhidctl.1,v 1.3 2001/12/30 07:24:07 pvalchev Exp $
-.\" $NetBSD: usbhidctl.1,v 1.10 2000/09/24 02:27:12 augustss Exp $
+.\" $OpenBSD: usbhidctl.1,v 1.4 2002/05/10 00:09:17 nate Exp $
+.\" $NetBSD: usbhidctl.1,v 1.14 2001/12/28 17:49:32 augustss Exp $
 .\"
-.\" Copyright (c) 2000 The NetBSD Foundation, Inc.
+.\" Copyright (c) 2001 The NetBSD Foundation, Inc.
 .\" All rights reserved.
 .\"
 .\" This code is derived from software contributed to The NetBSD Foundation
@@ -70,8 +70,8 @@
 .Op Ar item=value ...
 .Sh DESCRIPTION
 .Nm
-can be used to dump or modify the state of a USB HID (Human Interface Device).
-If a list of items is present on the command line, then
+can be used to output or modify the state of a USB HID (Human Interface
+Device).  If a list of items is present on the command line, then
 .Nm
 prints the current value of those items for the specified device.  If the
 .Fl w
@@ -83,6 +83,7 @@ The options are as follows:
 .Bl -tag -width Ds
 .It Fl a
 Show all items and their current values.
+This option fails if the device does not support the GET_REPORT command.
 .It Fl f Ar device
 Specify a path name for the device to operate on.  If
 .Ar device
@@ -94,9 +95,10 @@ An absolute path is taken to be the literal device pathname.
 Loop and dump the device data every time it changes.  Only 'input' items are
 displayed in this mode.
 .It Fl n
-Suppress printing of the item name when querying specific item values.
+Suppress printing of the item name when querying specific items.  Only output
+the current value.
 .It Fl r
-Dump the report descriptor.
+Dump the USB HID report descriptor.
 .It Fl t Ar table
 Specify a path name for the HID usage table file.
 .It Fl v
@@ -108,18 +110,91 @@ option.
 .Sh FILES
 .Pa /usr/share/misc/usb_hid_usages
 The default HID usage table.
+.Sh SYNTAX
+.Nm
+parses the names of items specified on the command line against the human
+interface items reported by the USB device.  Each human interface item is
+mapped from its native form to a human readable name, using the HID usage
+table file.  Command line items are compared with the generated item names,
+and the USB HID device is operated on when a match is found.
+.Pp
+Each human interface item is named by the
+.Qq page
+it appears in, the
+.Qq usage
+within that page, and the list of
+.Qq collections
+containing the item.  Each collection in turn is also identified by page, and
+the usage within that page.
+.Pp
+On the
+.Nm
+command line the page name is separated from the usage name with the character
+.Cm So : Sc .
+The collections are separated by the character
+.Cm So . Sc .
+.Pp
+As an alternative notation in items on the command line, the native numeric
+value for the page name or usage can be used instead of the full human
+readable page name or usage name.  Numeric values can be specified in decimal,
+octal or hexadecimal.
+.Sh EXAMPLES
+On a standard USB mouse the item
+.Dl Generic_Desktop:Mouse.Generic_Desktop:Pointer.Button:Button_2
+reflects the current status of button 2.  The
+.Qq button 2
+item is encapsulated within two collections, the
+.Qq Mouse
+collection in the
+.Qq Generic Desktop
+page, and the
+.Qq Pointer
+collection in the
+.Qq Generic Desktop
+page.  The item itself is the usage
+.Qq Button_2
+in the
+.Qq Button
+page.
+.Pp
+An item can generally be named by omitting one or more of the page names.  For
+example the
+.Qq button 2
+item would usually just be referred to on the command line as:
+.Dl usbhidctl -f /dev/mouse Mouse.Pointer.Button_2
+.Pp
+Items can also be named by referring to parts of the item name with the
+numeric representation of the native HID usage identifiers.  This is most
+useful when items are missing from the HID usage table.  The page identifier
+for the
+.Qq Generic Desktop
+page is 1, and the usage identifier for the usage
+.Qq Button_2
+is 2, so the following can be used to refer to the
+.Qq button 2
+item:
+.Dl usbhidctl -f /dev/mouse 1:Mouse.1:Pointer.Button:2
+.Pp
+Devices with human interface outputs can be manipulated with the
+.Fl w
+option.  For example, some USB mice have a Light Emitting Diode under software
+control as usage 2 under page 0xffff, in the
+.Qq Mouse
+collection.  The following can be used to switch this LED off:
+.Dl usbhidctl -f /dev/mouse -w Mouse.0xffff:2=0
 .Sh SEE ALSO
+.Xr usbhidaction 1 ,
 .Xr usbhid 3 ,
 .Xr uhid 4 ,
 .Xr usb 4
-.Sh AUTHOR
-David Sainty <David.Sainty@dtsp.co.nz>
 .Sh HISTORY
 The
 .Nm
 command first appeared in
 .Ox 3.0 .
+.Sh AUTHORS
+.An David Sainty Aq David.Sainty@dtsp.co.nz
 .Sh BUGS
-Some USB HID devices report multiple items with exactly the same description.
-The current naming scheme does not provide the means to specify which of the
-identically named items you are referring to.
+Some USB HID devices report multiple items with exactly the same usage
+identifiers.  The current naming scheme does not provide the means to specify
+which of a set of identically named items you are referring to.