Ux_Host_CDC_ACM Application Description
This application provides an example of Azure RTOS USBX stack usage
.
The application is designed to behave as a USB CDC_ACM Host, the code
provides required requests to properly enumerate CDC devices, CDC_ACM
class APIs to send or receive data and display data on UART
HyperTerminal.
The main entry function tx_application_define() is then called by
ThreadX during kernel start, at this stage, all USBx resources are
initialized. The application creates 3 threads with different
priorities:
- usbx_app_thread_entry (Priority : 10; Preemption threshold : 10)
used to initialize USB DRD HAL HCD driver and start the Host.
- cdc_acm_send_app_thread_entry (Priority : 30; Preemption threshold :
30) used to send data from host to device.
- cdc_acm_recieve_app_thread_entry (Priority : 30; Preemption
threshold : 30) used to receive data from the device.
Expected success
behavior
- When a CDC device is plugged to NUCLEO-C071RB board, a message will
be displayed on the UART HyperTerminal (STlink VCP) showing the Vendor
ID and Product ID of the attached device. The host must be able to
properly decode CDC_ACM class request data sent by the device. After
enumeration phase, a message will indicate that the device is ready for
use.
- The sent/received data are displayed on respective
Hyperterminals.
Error behaviors
Errors are detected (such as unsupported device, enumeration Fail)
and the corresponding message is displayed on the HyperTerminal.
Assumptions if any
User is familiar with USB 2.0 “Universal Serial BUS” specification
and CDC_ACM class specification.
Known limitations
- If the USB cable is unplugged then re-plugged, sometimes the data
are not received correctly by the STM32 USB host (some extra bytes
sent).
ThreadX usage hints
- ThreadX uses the Systick as time base, thus it is mandatory that the
HAL uses a separate time base through the TIM IPs.
- ThreadX is configured with 100 ticks/sec by default, this should be
taken into account when using delays or timeouts at application. It is
always possible to reconfigure it, by updating the
“TX_TIMER_TICKS_PER_SECOND” define in the “tx_user.h” file. The update
should be reflected in “tx_initialize_low_level.S” file too.
- ThreadX is disabling all interrupts during kernel start-up to avoid
any unexpected behavior, therefore all system related calls (HAL, BSP)
should be done either at the beginning of the application or inside the
thread entry functions.
- ThreadX offers the “tx_application_define()” function, that is
automatically called by the tx_kernel_enter() API. It is highly
recommended to use it to create all applications ThreadX related
resources (threads, semaphores, memory pools…) but it should not in any
way contain a system API call (HAL or BSP).
- Using dynamic memory allocation requires to apply some changes to
the linker file. ThreadX needs to pass a pointer to the first free
memory location in RAM to the tx_application_define() function, using
the “first_unused_memory” argument. This requires changes in the linker
files to expose this memory location.
- For EWARM add the following section into the .icf file:
place in RAM_region { last section FREE_MEM };
either define the RW_IRAM1 region in the ".sct" file
or modify the line below in "tx_initialize_low_level.S to match the memory region being used
LDR r1, =|Image$$RW_IRAM1$$ZI$$Limit|
- For STM32CubeIDE add the following section into the .ld file:
._threadx_heap :
{
. = ALIGN(8);
__RAM_segment_used_end__ = .;
. = . + 64K;
. = ALIGN(8);
} >RAM_D1 AT> RAM_D1
The simplest way to provide memory for ThreadX is to define a new section, see ._threadx_heap above.
In the example above the ThreadX heap size is set to 64KBytes.
The ._threadx_heap must be located between the .bss and the ._user_heap_stack sections in the linker script.
Caution: Make sure that ThreadX does not need more than the provided heap memory (64KBytes in this example).
Read more in STM32CubeIDE User Guide, chapter: "Linker script".
- The “tx_initialize_low_level.S” should be also modified to enable
the “USE_DYNAMIC_MEMORY_ALLOCATION” flag.
USBX usage hints
- The DTCM (0x20000000) memory region should not be used by
application in case USB DMA is enabled
- Should make sure to configure the USB pool memory region with
attribute “Non-Cacheable” to ensure coherency between CPU and USB
DMA
Keywords
Connectivity, USBX Host, ThreadX, USB, CDC_ACM, UART, USART
Hardware and Software
environment
- This application runs on STM32C07xx devices.
- This application has been tested with STMicroelectronics
NUCLEO-C071RB board revision MB2046-C071RB-B01 and can be easily
tailored to any other supported device and development board.
- NUCLEO-C071RB set-up:
- Plug the USB CDC_ACM device into the NUCLEO-C071RB board through
‘USB micro A-Male to A-Female’ cable to the connector:
- CN13 : to use USB High Speed DRD IP.
- Connect ST-Link cable to the PC USB port to display data on the
HyperTerminal.
A virtual COM port will then appear in the HyperTerminal:
- Hyperterminal configuration
- Data Length = 8 Bits
- One Stop Bit
- No parity
- BaudRate = 115200 baud
- Flow control: None
A second virtual COM port will then appear in the HyperTerminal when
plugging the device:
- Hyperterminal configuration
- Data Length = 8 Bits
- One Stop Bit
- No parity
- BaudRate = 9600 baud
- Flow control: None
- To send data from the USB CDC_ACM Host use the user push-button and
data will be received and displayed in the HyperTerminal connected to
the CDC ACM Device.
How to use it ?
In order to make the program work, you must do the following :
- Open your preferred toolchain
- Rebuild all files and load your image into target memory
- Run the application
Notes
The user has to check the list of the COM ports in Device Manager
to find out the number of the COM ports that have been assigned (by OS)
to the Stlink VCP.
The application uses the HSE clock as USB source clock.