From f13728c6e156f79f3b9286bcca9f3dcb4a22a285 Mon Sep 17 00:00:00 2001
From: Sebastian Zagrodzki <sebek@zagrodzki.net>
Date: Sun, 5 Feb 2017 16:20:58 +0100
Subject: [PATCH] Set the MaxIsoPacket field in the endpoint info if the
 endpoint is an isochronous endpoint. Use MaxIsoPacket as the iso packet size
 when preparing the iso transfer.

---
 usb/config.go | 19 +++++++++++++------
 usb/iso.go    |  8 +++-----
 2 files changed, 16 insertions(+), 11 deletions(-)

diff --git a/usb/config.go b/usb/config.go
index 9571174..62177e0 100644
--- a/usb/config.go
+++ b/usb/config.go
@@ -126,15 +126,22 @@ func newConfig(dev *C.libusb_device, cfg *C.struct_libusb_config_descriptor) Con
 			}
 			i.Endpoints = make([]EndpointInfo, 0, len(ends))
 			for _, end := range ends {
-				i.Endpoints = append(i.Endpoints, EndpointInfo{
+				ei := EndpointInfo{
 					Address:       uint8(end.bEndpointAddress),
 					Attributes:    uint8(end.bmAttributes),
 					MaxPacketSize: uint16(end.wMaxPacketSize),
-					//MaxIsoPacket:  uint32(C.libusb_get_max_iso_packet_size(dev, C.uchar(end.bEndpointAddress))),
-					PollInterval: uint8(end.bInterval),
-					RefreshRate:  uint8(end.bRefresh),
-					SynchAddress: uint8(end.bSynchAddress),
-				})
+					PollInterval:  uint8(end.bInterval),
+					RefreshRate:   uint8(end.bRefresh),
+					SynchAddress:  uint8(end.bSynchAddress),
+				}
+				if TransferType(ei.Attributes)&TRANSFER_TYPE_MASK == TRANSFER_TYPE_ISOCHRONOUS {
+					// bits 0-10 identify the packet size, bits 11-12 are the number of additional transactions per microframe.
+					// Don't use libusb_get_max_iso_packet_size, as it has a bug where it returns the same value
+					// regardless of alternative setting used, where different alternative settings might define different
+					// max packet sizes.
+					ei.MaxIsoPacket = uint32(end.wMaxPacketSize) & 0x07ff * (uint32(end.wMaxPacketSize)>>11&3 + 1)
+				}
+				i.Endpoints = append(i.Endpoints, ei)
 			}
 			descs = append(descs, i)
 		}
diff --git a/usb/iso.go b/usb/iso.go
index 3be4152..1044de3 100644
--- a/usb/iso.go
+++ b/usb/iso.go
@@ -37,10 +37,8 @@ func iso_callback(cptr unsafe.Pointer) {
 }
 
 func (end *endpoint) allocTransfer() *Transfer {
-	// Use libusb_get_max_iso_packet_size ?
 	const (
-		iso_packets = 8       // 128 // 242
-		packet_size = 2 * 960 // 1760
+		iso_packets = 8 // 128 // 242
 	)
 
 	xfer := C.libusb_alloc_transfer(C.int(iso_packets))
@@ -49,7 +47,7 @@ func (end *endpoint) allocTransfer() *Transfer {
 		return nil
 	}
 
-	buf := make([]byte, iso_packets*packet_size)
+	buf := make([]byte, iso_packets*end.EndpointInfo.MaxIsoPacket)
 	done := make(chan struct{}, 1)
 
 	xfer.dev_handle = end.Device.handle
@@ -60,7 +58,7 @@ func (end *endpoint) allocTransfer() *Transfer {
 	xfer.length = C.int(len(buf))
 	xfer.num_iso_packets = iso_packets
 
-	C.libusb_set_iso_packet_lengths(xfer, packet_size)
+	C.libusb_set_iso_packet_lengths(xfer, C.uint(end.EndpointInfo.MaxIsoPacket))
 	/*
 		pkts := *(*[]C.struct_libusb_packet_descriptor)(unsafe.Pointer(&reflect.SliceHeader{
 			Data: uintptr(unsafe.Pointer(&xfer.iso_packet_desc)),