Chapter 2 - USBX Device Stack Installation

Host Considerations

Computer Type

Embedded development is usually performed on Windows PC or Unix host computers. After the application is compiled, linked, and located on the host, it is downloaded to the target hardware for execution.

Download Interfaces

Usually the target download is done over an RS-232 serial interface, although parallel interfaces, USB, and Ethernet are becoming more popular. See the development tool documentation for available options.

Debugging Tools

Debugging is done typically over the same link as the program image download. A variety of debuggers exist, ranging from small monitor programs running on the target through Background Debug Monitor (BDM) and In-Circuit Emulator (ICE) tools. The ICE tool provides the most robust debugging of actual target hardware.

Required Hard Disk Space

The source code for USBX is delivered in ASCII format and requires approximately 500 KBytes of space on the host computer’s hard disk.

Target Considerations

USBX requires between 24 KBytes and 64 KBytes of Read Only Memory (ROM) on the target in host mode. The amount of memory required is dependent on the type of controller used and the USB classes linked to USBX. Another 32 KBytes of the target’s Random Access Memory (RAM) are required for USBX global data structures and memory pool. This memory pool can also be adjusted depending on the expected number of devices on the USB and the type of USB controller. The USBX device side requires roughly 10-12 K of ROM depending on the type of device controller. The RAM memory usage depends on the type of class emulated by the device.

USBX also relies on ThreadX semaphores, mutexes, and threads for multiple thread protection, and I/O suspension and periodic processing for monitoring the USB bus topology.

Product Distribution

USBX can be obtained from our public source code repository at https://github.com/eclipse-threadx/usbx/.

The following is a list of several important files in the repository.

ux_api.h: This C header file contains all system equates, data structures, and service prototypes.
ux_port.h: This C header file contains all development-tool-specific data definitions and structures.
ux.lib: This is the binary version of the USBX C library. It is distributed with the standard package.
demo_usbx.c: The C file containing a simple USBX demo

All filenames are in lower-case. This naming convention makes it easier to convert the commands to Unix development platforms.

USBX Installation

USBX is installed by cloning the GitHub repository to your local machine. The following is typical syntax for creating a clone of the USBX repository on your PC:

    git clone https://github.com/eclipse-threadx/usbx

Alternatively you can download a copy of the repository using the download button on the GitHub main page.

You will also find instructions for building the USBX library on the front page of the online repository.

The following general instructions apply to virtually any installation:

Use the same directory in which you previously installed ThreadX on the host hard drive. All USBX names are unique and will not interfere with the previous USBX installation.
Add a call to ux_system_initialize at or near the beginning of tx_application_define. This is where the USBX resources are initialized.
Add a call to ux_device_stack_initialize.
Add one or more calls to initialize the required USBX classes (either host and/or devices classes)
Add one or more calls to initialize the device controller available in the system.

It may be required to modify the tx_low_level_initialize.c file to add low-level hardware initialization and interrupt vector routing. This is specific to the hardware platform and will not be discussed here.

Compile application source code and link with the USBX and ThreadX run time libraries (FileX and/or NetX Duo may also be required if the USB storage class and/or USB network classes are to be compiled in), ux.a (or ux.lib) and tx.a (or tx.lib). The resulting can be downloaded to the target and executed!

Configuration Options

There are several configuration options for building the USBX library. All options are located in the ux_user.h.

The list below details each configuration option.

Configuration Option	Description
UX_PERIODIC_RATE	This value represents how many ticks per seconds for a specific hardware platform. The default is 1000 indicating 1 tick per millisecond.
UX_THREAD_STACK_SIZE	This value is the size of the stack in bytes for the USBX threads. It can be typically 1024 bytes or 2048 bytes depending on the processor used and the host controller.
UX_THREAD_PRIORITY_ENUM	This is the ThreadX priority value for the USBX enumeration threads that monitors the bus topology.
UX_THREAD_PRIORITY_CLASS	This is the ThreadX priority value for the standard USBX threads.
UX_THREAD_PRIORITY_KEYBOARD	This is the ThreadX priority value for the USBX HID keyboard class.
UX_THREAD_PRIORITY_DCD	This is the ThreadX priority value for the device controller thread.
UX_NO_TIME_SLICE	This value actually defines the time slice that will be used for threads. For example, if defined to 0, the ThreadX target port does not use time slices.
UX_MAX_SLAVE_CLASS_DRIVER	This is the maximum number of USBX classes that can be registered via ux_device_stack_class_register.
UX_MAX_SLAVE_LUN	This value represents the current number of SCSI logical units represented in the device storage class driver.
UX_SLAVE_CLASS_STORAGE_INCLUDE_MMC	If defined, the storage class will handle Multi-Media Commands (MMC) that is, DVD-ROM.
UX_DEVICE_CLASS_CDC_ECM_NX_PKPOOL_ENTRIES	This value represents the number of NetX packets in the CDC-ECM class' packet pool. The default is 16.
UX_SLAVE_REQUEST_CONTROL_MAX_LENGTH	This value represents the maximum number of bytes received on a control endpoint in the device stack. The default is 256 bytes but can be reduced in memory constraint environments.
UX_DEVICE_CLASS_HID_EVENT_BUFFER_LENGTH	This value represents the maximum length in bytes of a HID report.
UX_DEVICE_CLASS_HID_MAX_EVENTS_QUEUE	This value represents the maximum number of HID reports that can be queued at once.
UX_SLAVE_REQUEST_DATA_MAX_LENGTH	This value represents the maximum number of bytes received on a bulk endpoint in the device stack. The default is 4096 bytes but can be reduced in memory constraint environments.
UX_DEVICE_BIDIRECTIONAL_ENDPOINT_SUPPORT	If defined, the device side enables bi-directional-endpoints support, e.g., endpoints addressed 0x01 and 0x81. Otherwise (the default case), endpoint number must be unique in same configuration. Note the feature must be used with compatible DCD and peripheral.

Configuration Option

Description

UX_PERIODIC_RATE

This value represents how many ticks per seconds for a specific hardware platform. The default is 1000 indicating 1 tick per millisecond.

UX_THREAD_STACK_SIZE

This value is the size of the stack in bytes for the USBX threads. It can be typically 1024 bytes or 2048 bytes depending on the processor used and the host controller.

UX_THREAD_PRIORITY_ENUM

This is the ThreadX priority value for the USBX enumeration threads that monitors the bus topology.

UX_THREAD_PRIORITY_CLASS

This is the ThreadX priority value for the standard USBX threads.

UX_THREAD_PRIORITY_KEYBOARD

This is the ThreadX priority value for the USBX HID keyboard class.

UX_THREAD_PRIORITY_DCD

This is the ThreadX priority value for the device controller thread.

UX_NO_TIME_SLICE

This value actually defines the time slice that will be used for threads. For example, if defined to 0, the ThreadX target port does not use time slices.

UX_MAX_SLAVE_CLASS_DRIVER

This is the maximum number of USBX classes that can be registered via ux_device_stack_class_register.

UX_MAX_SLAVE_LUN

This value represents the current number of SCSI logical units represented in the device storage class driver.

UX_SLAVE_CLASS_STORAGE_INCLUDE_MMC

If defined, the storage class will handle Multi-Media Commands (MMC) that is, DVD-ROM.

UX_DEVICE_CLASS_CDC_ECM_NX_PKPOOL_ENTRIES

This value represents the number of NetX packets in the CDC-ECM class' packet pool. The default is 16.

UX_SLAVE_REQUEST_CONTROL_MAX_LENGTH

This value represents the maximum number of bytes received on a control endpoint in the device stack. The default is 256 bytes but can be reduced in memory constraint environments.

UX_DEVICE_CLASS_HID_EVENT_BUFFER_LENGTH

This value represents the maximum length in bytes of a HID report.

UX_DEVICE_CLASS_HID_MAX_EVENTS_QUEUE

This value represents the maximum number of HID reports that can be queued at once.

UX_SLAVE_REQUEST_DATA_MAX_LENGTH

This value represents the maximum number of bytes received on a bulk endpoint in the device stack. The default is 4096 bytes but can be reduced in memory constraint environments.

UX_DEVICE_BIDIRECTIONAL_ENDPOINT_SUPPORT

If defined, the device side enables bi-directional-endpoints support, e.g., endpoints addressed 0x01 and 0x81. Otherwise (the default case), endpoint number must be unique in same configuration. Note the feature must be used with compatible DCD and peripheral.

Source Code Tree

The USBX files are provided in several directories.

In order to make the files recognizable by their names, the following convention has been adopted:

File Suffix Name	File description
ux_host_stack	usbx host stack core files
ux_host_class	usbx host stack classes files
ux_hcd	usbx host stack controller driver files
ux_device_stack	usbx device stack core files
ux_device_class	usbx device stack classes files
ux_dcd	usbx device stack controller driver files
ux_otg	usbx otg controller driver related files
ux_pictbridge	usbx pictbridge files
ux_utility	usbx utility functions
demo_usbx	demonstration files for USBX

File Suffix Name

File description

ux_host_stack

usbx host stack core files

ux_host_class

usbx host stack classes files

ux_hcd

usbx host stack controller driver files

ux_device_stack

usbx device stack core files

ux_device_class

usbx device stack classes files

ux_dcd

usbx device stack controller driver files

ux_otg

usbx otg controller driver related files

ux_pictbridge

usbx pictbridge files

ux_utility

usbx utility functions

demo_usbx

demonstration files for USBX

Initialization of USBX resources

USBX has its own memory manager. The memory needs to be allocated to USBX before the host or device side of USBX is initialized. USBX memory manager can accommodate systems where memory can be cached.

The following function initializes USBX memory resources with 128 K of regular memory and no separate pool for cache safe memory:

/* Initialize USBX Memory */
ux_system_initialize(memory_pointer,(128*1024),UX_NULL,0);

The prototype for the ux_system_initialize is as follows:

UINT ux_system_initialize(VOID *regular_memory_pool_start,
        ULONG regular_memory_size,
        VOID *cache_safe_memory_pool_start,
        ULONG cache_safe_memory_size);

Input parameters:

Parameter	Description
VOID *regular_memory_pool_start	Beginning of the regular memory pool
ULONG regular_memory_size	Size of the regular memory pool
VOID *cache_safe_memory_pool_start	Beginning of the cache safe memory pool
ULONG cache_safe_memory_size	Size of the cache safe memory pool

Parameter

Description

VOID *regular_memory_pool_start

Beginning of the regular memory pool

ULONG regular_memory_size

Size of the regular memory pool

VOID *cache_safe_memory_pool_start

Beginning of the cache safe memory pool

ULONG cache_safe_memory_size

Size of the cache safe memory pool

Not all systems require the definition of cache safe memory. In such a system, the values passed during the initialization for the memory pointer will be set to UX_NULL and the size of the pool to 0. USBX will then use the regular memory pool in lieu of the cache safe pool.

In a system where the regular memory is not cache safe and a controller requires to perform DMA memory it is necessary to define a memory pool in a cache safe zone.

Uninitialization of USBX resources

USBX can be terminated by releasing its resources. Prior to terminating usbx, all classes and controller resources need to be terminated properly. The following function uninitializes USBX memory resources:

/* Unitialize USBX Resources */

ux_system_uninitialize();

The prototype for the ux_system_initialize is as follows:

UINT ux_system_uninitialize(VOID);

Definition of USB Device Controller

Only one USB device controller can be defined at any time to operate in device mode. The application initialization file should contain this definition. The following line performs the definition of a generic usb controller:

ux_dcd_controller_initialize(0x7BB00000, 0, 0xB7A00000);

The USB device initialization has the following prototype:

UINT ux_dcd_controller_initialize(ULONG dcd_io,
    ULONG dcd_irq, ULONG dcd_vbus_address);

with the following parameters:

Parameter	Description
ULONG dcd_io	Address of the controller IO
ULONG dcd_irq	Interrupt used by the controller
ULONG dcd_vbus_address	Address of the VBUS GPIO

Parameter

Description

ULONG dcd_io

Address of the controller IO

ULONG dcd_irq

Interrupt used by the controller

ULONG dcd_vbus_address

Address of the VBUS GPIO

The following example is the initialization of USBX in device mode with the storage device class and a generic controller:

/* Initialize USBX Memory */

ux_system_initialize(memory_pointer,(128*1024), 0, 0);

/* The code below is required for installing the device portion of USBX */
status = ux_device_stack_initialize(&device_framework_high_speed,
    DEVICE_FRAMEWORK_LENGTH_HIGH_SPEED, &device_framework_full_speed,
    DEVICE_FRAMEWORK_LENGTH_FULL_SPEED, &string_framework,
    STRING_FRAMEWORK_LENGTH, &language_id_framework,
    LANGUAGE_ID_FRAMEWORK_LENGTH, UX_NULL);

/* If status equals UX_SUCCESS, installation was successful. */

/* Store the number of LUN in this device storage instance: single LUN. */
storage_parameter.ux_slave_class_storage_parameter_number_lun = 1;

/* Initialize the storage class parameters for reading/writing to the Flash Disk. */
storage_parameter.ux_slave_class_storage_parameter_lun[0].ux_slave_class_storage_media_last_lba = 0x1e6bfe;
storage_parameter.ux_slave_class_storage_parameter_lun[0].ux_slave_class_storage_media_block_length = 512;
storage_parameter.ux_slave_class_storage_parameter_lun[0].ux_slave_class_storage_media_type = 0;
storage_parameter.ux_slave_class_storage_parameter_lun[0].ux_slave_class_storage_media_removable_flag = 0x80;
storage_parameter.ux_slave_class_storage_parameter_lun[0].ux_slave_class_storage_media_read = tx_demo_thread_flash_media_read;
storage_parameter.ux_slave_class_storage_parameter_lun[0].ux_slave_class_storage_media_write = tx_demo_thread_flash_media_write;
storage_parameter.ux_slave_class_storage_parameter_lun[0].ux_slave_class_storage_media_status = tx_demo_thread_flash_media_status;

/* Initialize the device storage class. The class is connected with interface 0 */
status = ux_device_stack_class_register(ux_system_slave_class_storage_name ux_device_class_storage_entry,
    ux_device_class_storage_thread,0, (VOID *)&storage_parameter);

/* Register the device controllers available in this system */
status = ux_dcd_controller_initialize(0x7BB00000, 0, 0xB7A00000);

/* If status equals UX_SUCCESS, registration was successful. */

Troubleshooting

USBX is delivered with a demonstration file and a simulation environment. It is always a good idea to get the demonstration platform running first—either on the target hardware or a specific demonstration platform.

USBX Version ID

The current version of USBX is available both to the user and the application software during run-time. The programmer can obtain the USBX version from examination of the ux_port.h file. In addition, this file also contains a version history of the corresponding port. Application software can obtain the USBX version by examining the global string _ux_version_id, which is defined in ux_port.h.