From 273ade90da6108435ba9827d88b3b2f245c98045 Mon Sep 17 00:00:00 2001
From: robertl <robertl>
Date: Sun, 23 Jul 2006 19:45:12 +0000
Subject: [PATCH] Correctly implement zero byte write after packet that's a
 multiple of frame size.

---
 jeeps/gpslibusb.c    |  4 ++++
 jeeps/gpsusbcommon.c | 12 ++++++++++++
 jeeps/gpsusbcommon.h |  1 +
 jeeps/gpsusbwin.c    | 10 ++--------
 4 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/jeeps/gpslibusb.c b/jeeps/gpslibusb.c
index dcaa8bd63..722635f21 100644
--- a/jeeps/gpslibusb.c
+++ b/jeeps/gpslibusb.c
@@ -54,6 +54,7 @@ typedef struct {
 static int gusb_intr_in_ep;
 static int gusb_bulk_out_ep;
 static int gusb_bulk_in_ep;
+static gusb_llops_t libusb_llops;
 
 static usb_dev_handle *udev;
 static void garmin_usb_scan(libusb_unit_data *, int);
@@ -71,6 +72,7 @@ gusb_libusb_send(const garmin_usb_packet *opkt, size_t sz)
 				usb_strerror());
 		}
 	}
+
 	return r;
 }
 
@@ -214,10 +216,12 @@ garmin_usb_start(struct usb_device *dev)
 		fatal("Claim interfaced failed: %s\n", usb_strerror());
 	}
 
+	libusb_llops.max_tx_size = dev->descriptor.bMaxPacketSize0;
 
 	for (i = 0; i < dev->config->interface->altsetting->bNumEndpoints; i++) {
 		struct usb_endpoint_descriptor * ep;
 		ep = &dev->config->interface->altsetting->endpoint[i];
+
 		switch (ep->bmAttributes & USB_ENDPOINT_TYPE_MASK) {
 #define EA(x) x & USB_ENDPOINT_ADDRESS_MASK
 			case USB_ENDPOINT_TYPE_BULK:
diff --git a/jeeps/gpsusbcommon.c b/jeeps/gpsusbcommon.c
index a75e90f1b..35ac8d684 100644
--- a/jeeps/gpsusbcommon.c
+++ b/jeeps/gpsusbcommon.c
@@ -170,6 +170,18 @@ gusb_cmd_send(const garmin_usb_packet *opkt, size_t sz)
 
 		GPS_Diag("(%-8s%s)\n", m1, m2 ? m2 : "");
         }
+	/*
+	 * Recursion, when used in a disciplined way, can be our friend.
+	 * 
+	 * The Garmin protocol requires that packets that are exactly
+	 * a multiple of the max tx size be followed by a zero length
+	 * packet.  Do that here so we can see it in debugging traces.
+	 */
+
+	if (sz && !(sz % gusb_llops->max_tx_size)) {
+		gusb_cmd_send(opkt, 0);
+	}
+
 	return (rv);
 }
 
diff --git a/jeeps/gpsusbcommon.h b/jeeps/gpsusbcommon.h
index 677e75789..b0865f5f0 100644
--- a/jeeps/gpsusbcommon.h
+++ b/jeeps/gpsusbcommon.h
@@ -32,6 +32,7 @@ typedef struct gusb_llops {
 	gusb_llop_get  llop_get_bulk;
 	gusb_llop_send llop_send;
 	gusb_llop_close llop_close;
+	int max_tx_size;
 } gusb_llops_t;
 
 /* Provided by the common code. */
diff --git a/jeeps/gpsusbwin.c b/jeeps/gpsusbwin.c
index 8e003ea44..d823738f0 100644
--- a/jeeps/gpsusbwin.c
+++ b/jeeps/gpsusbwin.c
@@ -72,7 +72,6 @@ gusb_win_get(garmin_usb_packet *ibuf, size_t sz)
 	DWORD rxed = GARMIN_USB_INTERRUPT_DATA_SIZE;
 	unsigned char *buf = (unsigned char *) &ibuf->dbuf;
 	int tsz=0;
-	unsigned char *obuf = buf;
 
 	while (sz) {
 		/* The driver wrongly (IMO) rejects reads smaller than 
@@ -118,13 +117,7 @@ gusb_win_send(const garmin_usb_packet *opkt, size_t sz)
 	WriteFile(usb_handle, obuf, sz, &rsz, NULL);
 
 	if (rsz != sz) {
-		fatal ("Error sending %d bytes.   Successfully sent %d\n", sz, rsz);
-	}
-
-	if (0 == sz % usb_tx_packet_size) {
-		DWORD sz2;
-		GPS_Diag("Writing padding buffer.\n");
-		WriteFile(usb_handle, 0, 0, &sz2, NULL);
+		fatal ("Error sending %d bytes.   Successfully sent %ld\n", sz, rsz);
 	}
 
 	return rsz;
@@ -177,6 +170,7 @@ HANDLE * garmin_usb_start(HDEVINFO* hdevinfo, SP_DEVICE_INTERFACE_DATA *infodata
 	    &size, NULL)) {
                 fatal("Couldn't get USB packet size.\n");
         }
+	win_llops.max_tx_size = usb_tx_packet_size;
 
 	gusb_syncup();
 
-- 
2.30.2