Mike R / USBDevice

USB device stack, with KL25Z fixes for USB 3.0 hosts and sleep/resume interrupt handling

Dependents:   frdm_Slider_Keyboard idd_hw2_figlax_PanType idd_hw2_appachu_finger_chording idd_hw3_AngieWangAntonioDeLimaFernandesDanielLim_BladeSymphony ... more

Fork of USBDevice by mbed official

This is an overhauled version of the standard mbed USB device-side driver library, with bug fixes for KL25Z devices. It greatly improves reliability and stability of USB on the KL25Z, especially with devices using multiple endpoints concurrently.

I've had some nagging problems with the base mbed implementation for a long time, manifesting as occasional random disconnects that required rebooting the device. Recently (late 2015), I started implementing a USB device on the KL25Z that used multiple endpoints, and suddenly the nagging, occasional problems turned into frequent and predictable crashes. This forced me to delve into the USB stack and figure out what was really going on. Happily, the frequent crashes made it possible to track down and fix the problems. This new version is working very reliably in my testing - the random disconnects seem completely eradicated, even under very stressful conditions for the device.

Summary

• Overall stability improvements
• USB 3.0 host support
• Stalled endpoint fixes
• Sleep/resume notifications
• Smaller memory footprint
• General code cleanup

Update - 2/15/2016

My recent fixes introduced a new problem that made the initial connection fail most of the time on certain hosts. It's not clear if the common thread was a particular type of motherboard or USB chip set, or a specific version of Windows, or what, but several people ran into it. We tracked the problem down to the "stall" fixes in the earlier updates, which we now know weren't quite the right fixes after all. The latest update (2/15/2016) fixes this. It has new and improved "unstall" handling that so far works well with diverse hosts.

Race conditions and overall stability

The base mbed KL25Z implementation has a lot of problems with "race conditions" - timing problems that can happen when hardware interrupts occur at inopportune moments. The library shares a bunch of static variable data between interrupt handler context and regular application context. This isn't automatically a bad thing, but it does require careful coordination to make sure that the interrupt handler doesn't corrupt data that the other code was in the middle of updating when an interrupt occurs. The base mbed code, though, doesn't do any of the necessary coordination. This makes it kind of amazing that the base code worked at all for anyone, but I guess the interrupt rate is low enough in most applications that the glitch rate was below anyone's threshold to seriously investigate.

This overhaul adds the necessary coordination for the interrupt handlers to protect against these data corruptions. I think it's very solid now, and hopefully entirely free of the numerous race conditions in the old code. It's always hard to be certain that you've fixed every possible bug like this because they strike (effectively) at random, but I'm pretty confident: my test application was reliably able to trigger glitches in the base code in a matter of minutes, but the same application (with the overhauled library) now runs for days on end without dropping the connection.

Stalled endpoint fixes

USB has a standard way of handling communications errors called a "stall", which basically puts the connection into an error mode to let both sides know that they need to reset their internal states and sync up again. The original mbed version of the USB device library doesn't seem to have the necessary code to recover from this condition properly. The KL25Z hardware does some of the work, but it also seems to require the software to take some steps to "un-stall" the connection. (I keep saying "seems to" because the hardware reference material is very sketchy about all of this. Most of what I've figured out is from observing the device in action with a Windows host.) This new version adds code to do the necessary re-syncing and get the connection going again, automatically, and transparently to the user.

USB 3.0 Hosts

The original mbed code sometimes didn't work when connecting to hosts with USB 3.0 ports. This didn't affect every host, but it affected many of them. The common element seemed to be the Intel Haswell chip set on the host, but there may be other chip sets affected as well. In any case, the problem affected many PCs from the Windows 7 and 8 generation, as well as many Macs. It was possible to work around the problem by avoiding USB 3.0 ports - you could use a USB 2 port on the host, or plug a USB 2 hub between the host and device. But I wanted to just fix the problem and eliminate the need for such workarounds. This modified version of the library has such a fix, which so far has worked for everyone who's tried.

Sleep/resume notifications

This modified version also contains an innocuous change to the KL25Z USB HAL code to handle sleep and resume interrupts with calls to suspendStateChanged(). The original KL25Z code omitted these calls (and in fact didn't even enable the interrupts), but I think this was an unintentional oversight - the notifier function is part of the generic API, and other supported boards all implement it. I use this feature in my own application so that I can distinguish sleep mode from actual disconnects and handle the two conditions correctly.

Smaller memory footprint

The base mbed version of the code allocates twice as much memory for USB buffers as it really needed to. It looks like the original developers intended to implement the KL25Z USB hardware's built-in double-buffering mechanism, but they ultimately abandoned that effort. But they left in the double memory allocation. This version removes that and allocates only what's actually needed. The USB buffers aren't that big (128 bytes per endpoint), so this doesn't save a ton of memory, but even a little memory is pretty precious on this machine given that it only has 16K.

(I did look into adding the double-buffering support that the original developers abandoned, but after some experimentation I decided they were right to skip it. It just doesn't seem to mesh well with the design of the rest of the mbed USB code. I think it would take a major rewrite to make it work, and it doesn't seem worth the effort given that most applications don't need it - it would only benefit applications that are moving so much data through USB that they're pushing the limits of the CPU. And even for those, I think it would be a lot simpler to build a purely software-based buffer rotation mechanism.)

General code cleanup

The KL25Z HAL code in this version has greatly expanded commentary and a lot of general cleanup. Some of the hardware constants were given the wrong symbolic names (e.g., EVEN and ODD were reversed), and many were just missing (written as hard-coded numbers without explanation). I fixed the misnomers and added symbolic names for formerly anonymous numbers. Hopefully the next person who has to overhaul this code will at least have an easier time understanding what I thought I was doing!

/* Copyright (c) 2010-2011 mbed.org, MIT License
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* substantial portions of the Software.
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* BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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*/

#ifndef USBAUDIO_TYPES_H
#define USBAUDIO_TYPES_H


#define DEFAULT_CONFIGURATION (1)

// Audio Request Codes
#define REQUEST_SET_CUR     0x01
#define REQUEST_GET_CUR     0x81
#define REQUEST_SET_MIN     0x02
#define REQUEST_GET_MIN     0x82
#define REQUEST_SET_MAX     0x03
#define REQUEST_GET_MAX     0x83
#define REQUEST_SET_RES     0x04
#define REQUEST_GET_RES     0x84

#define MUTE_CONTROL        0x01
#define VOLUME_CONTROL      0x02


// Audio Descriptor Sizes
#define CONTROL_INTERFACE_DESCRIPTOR_LENGTH       0x09
#define STREAMING_INTERFACE_DESCRIPTOR_LENGTH     0x07
#define INPUT_TERMINAL_DESCRIPTOR_LENGTH          0x0C
#define OUTPUT_TERMINAL_DESCRIPTOR_LENGTH         0x09
#define FEATURE_UNIT_DESCRIPTOR_LENGTH            0x09
#define STREAMING_ENDPOINT_DESCRIPTOR_LENGTH      0x07

// Audio Format Type Descriptor Sizes
#define FORMAT_TYPE_I_DESCRIPTOR_LENGTH   0x0b

#define AUDIO_CLASS                       0x01
#define SUBCLASS_AUDIOCONTROL             0x01
#define SUBCLASS_AUDIOSTREAMING           0x02

// Audio Descriptor Types
#define INTERFACE_DESCRIPTOR_TYPE         0x24
#define ENDPOINT_DESCRIPTOR_TYPE          0x25

// Audio Control Interface Descriptor Subtypes
#define CONTROL_HEADER                    0x01
#define CONTROL_INPUT_TERMINAL            0x02
#define CONTROL_OUTPUT_TERMINAL           0x03
#define CONTROL_FEATURE_UNIT              0x06

// USB Terminal Types
#define TERMINAL_USB_STREAMING            0x0101

// Predefined Audio Channel Configuration Bits
// Mono
#define CHANNEL_M                         0x0000
#define CHANNEL_L                         0x0001  /* Left Front */
#define CHANNEL_R                         0x0002  /* Right Front */

// Feature Unit Control Bits
#define CONTROL_MUTE                      0x0001
#define CONTROL_VOLUME                    0x0002

// Input Terminal Types
#define TERMINAL_MICROPHONE               0x0201

// Output Terminal Types
#define TERMINAL_SPEAKER                  0x0301
#define TERMINAL_HEADPHONES               0x0302

// Audio Streaming Interface Descriptor Subtypes
#define STREAMING_GENERAL                 0x01
#define STREAMING_FORMAT_TYPE             0x02

// Audio Data Format Type I Codes
#define FORMAT_PCM                        0x0001

// Audio Format Types
#define FORMAT_TYPE_I                     0x01

// Audio Endpoint Descriptor Subtypes
#define ENDPOINT_GENERAL                  0x01

#endif