Atmel AVR4921: ASF - USB Device Stack Differences between ASF V1 and V2
Features
• Advantages
• Implementation differences
• Integration
• Migration from stack V1 to stack V2
1 Introduction
Atmel® has always provided a USB device stack to support AVR® products with a USB hardware interface. The Atmel AT32UC3A and Atmel AT32UC3B products are supported in Atmel AVR Software Framework (ASF) version 1 (V1) with a specific USB device stack. Since ASF version 2 (V2), a new USB device stack has been delivered to support all AVR products. The aim of this document is to explain the implementation advantages of the new USB device stack for AT32UC3A and AT32UC3B MCUs as well as the major differences from the former USB device stack.
NOTE In the rest of the document, the former USB stack will be referred to as USB Device stack V1, while new stack will be referred to as USB device stack V2.
8-bit Atmel
Microcontrollers Application Note
Rev. 8411A-AVR-08/11
2 Abbreviations
ASF AVR Software Framework USB Universal serial bus
Atmel AVR4921
3 Advantages
The following list shows the advantages of USB device stack V2 over USB device stack V1:
• All Atmel AVR products are supported: Atmel megaAVR®, Atmel AVR XMEGA®, and Atmel AVR UC3
Eases migration between all AVR products
• DMA is used when applicable for all USB transfers
Increases speed and reduces CPU usage
• The stack is managed only by interrupt
Reduces latency
Avoids any task scheduler
• The implementation supports all AVR power reduction features
Helps to create a very low-power device
• All USB protocol errors are taken into account
Robust software solution
• Better software architecture
Easiest to use
No USB-specific code in the application
Reduces development time
• Various detailed application notes are available
Reduces development time
• A new USB class implementation is supported
Provides peripheral health device class (PHDC)
• The V2 and V1 footprints (code/RAM size) are the same
Does not require a larger memory target space
All classes available in USB device stack V1 will be supported by USB device stack V2.
Table 3-1. USB device class status.
Class ASF V1 status ASF V2 status
Template No Q3 2011
Composite (HIDs, CDC, MSC) No ASF2.3.2
HID mouse Available ASF2.3.2
HID keyboard No ASF2.3.2
HID generic No ASF2.3.2
Mass storage (MSC) Available ASF2.3.2
Communication (CDC) Available ASF2.3.2
Personal health device (PHDC) No ASF2.3.2
Audio Available Q4 2011
Device firmware upgrade (DFU) Available Q3 2011
4.1 File organization
4.1.1 USB device stack V1
The specific USB device stack for Atmel AVR UC3 A and Atmel AVR UC3 B 32-bit products is prefixed by a _asf_v1 folder in the ASF package, and is stored in the following folders:
File Path
• USB constant defines avr32/services/usb/_asf_v1/class/
usb_ids.h
• USB device core files avr32/drivers/usbb/_asf_v1/enum/
usb_task.c/h
device/usb_device_task.c/h device/usb_standard_request.c/h
• Class protocol files avr32/services/usb/_asf_v1/class/foo/
foo.h
• Class and USB descriptor files duplicated in application folder device_class_task.c/h
usb_specific_request.c/h usb_descriptors.c/h
• Driver files for AVR UC3 avr32/drivers/usbb/_asf_v1/
usb_drv.c/h usbb.h
• Configuration files
usb_conf.h (This configuration file is mandatory) 4.1.2 USB device stack V2
The USB device stack V2 for all AVR products is stored in the following folders:
File Path
• USB constant defines common/services/usb/
usb_protocol.h (from usb.org) usb_atmel.h (from Atmel)
• USB device core files common/services/usb/udc/
udc.c/h udc_desc.h udi.h udd.h
• Class protocol files common/services/usb/class/foo/
usb_protocol_foo.h
• Class and USB descriptor files common/services/usb/class/foo/device/
Atmel AVR4921
udi_foo.c/h udi_foo_desc.c udi_foo_conf.h
• Driver files for AVR UC3 avr32/drivers/
usbb/usbb_device.c/h usbb/usbb_otg.h usbc/usbc_device.c/h usbc/usbc_otg.h
• Driver files for AVR XMEGA xmega/drivers/
usb/usb_device.c/h
• Configuration files
usb_conf.h (This configuration file is mandatory)
4.2 Integration
4.2.1 USB device stack V1
The USB device stack V1 requires the initialization and scheduling of USB core tasks and class tasks in the main code section. It also requires the class implementation and USB descriptors in the user application:
Main code section
// Initialize USB clock (on PLL1) pcl_configure_usb_clock();
// Initialize USB task usb_task_init();
// Initialize device mouse USB task device_mouse_hid_task_init();
// No OS here. Need to call each task in round-robin mode.
while (true) {
usb_task();
device_mouse_hid_task();
}
Class implementation and user interface, for example:
device_class_task.c/h Class setup implementation:
usb_specific_request.c/h USB descriptors:
usb_descriptors.c/h 4.2.2 USB device stack V2
The USB device stack V2 requires the clock manager software module (/common/services/clock) and sleep manager software module (/common/services/sleepmgr) from ASF. Intialization of the clock, sleep manager and
interface.
For more information concerning integration, refer to the Atmel AVR4903 to AVR4909 USB device class application notes.
Main code section
// Initialize the sleep manager service sleepmgr_init();
// Initialize the clock service sysclk_init();
// Enable USB Stack Device udc_start();
User interface only, for example:
ui.c/h
Atmel AVR4921
5 Migration from stack V1 to stack V2
The USB device stack V2 requires the clock manager software module and sleep manager software module from ASF V2. In the USB device stack V1 applications, however, clock configuration and sleep mode control are done by the user application code, which calls UC3 clock and sleep drivers.
Because of this fundamental difference between stack V1 and stack V2, there can be no straightforward migration. It is recommended to start again from existing V2 example projects.
Moving to USB device stack V2 in ASF offers greater robustness as well as ease of use for both beginners and advanced users when developing firmware with USB. It also adds performance in managing low-level USB, and takes advantage of all USB hardware features implemented in Atmel AVR products.
The stack provides full support of many USB classes, with example projects in ASF and Atmel AVR Studio® 5.
The stack allows the sharing of code among Atmel megaAVR, AVR XMEGA and AVR UC3 products. Maintenance and portability from one architecture to another is also improved.
Atmel AVR4921
7 Table of contents
Features... 1
1 Introduction ... 1
2 Abbreviations ... 2
3 Advantages... 3
4 Implementation ... 4
4.1 File organization ... 4
4.1.1 USB device stack V1... 4
4.1.2 USB device stack V2... 4
4.2 Integration... 5
4.2.1 USB device stack V1... 5
4.2.2 USB device stack V2... 5
5 Migration from stack V1 to stack V2 ... 7
6 Conclusion ... 8
7 Table of contents ... 9
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