AVR8
Contents
Introduction
Embedded microcontroller units are spreading in thousands of applications, ranging from single to distributed systems, control applications, multimedia, communication, medical applications and many others. Modern microcontrollers, which are growing in computational power, speed and interfacing capabilities, are more and more feeling the need of tools to make the development of complex scalable applications easier.
This manual describes the porting details of the ERIKA Enterprise v3 kernel(s) for the Atmel (now Microchip) families of microcontrollers which supports 8/16-bit RISC AVR cores (aka AVR8).
ERIKA Enterprise v3 and RT-Druid v3 for AVR8
Embedded applications often require tight control on the temporal behavior of each single activity in the system. Real-time complex system systems such as Wireless Sensor Networks are nowadays deployed in academic and industrial environments. The very limited set of resources available in the popular hardware platforms, and the diversified domains of WSN applications, require the adoption of an Operating System responding to the following pre-requisites:
- minimum footprint to fit the limited RAM capacity (of the order of few KB);
- tunable scheduling algorithm to handle the execution of the tasks;
- an application interface acting on the kernel layer and well decoupled from OS service implementation.
ERIKA Enterprise v3 and RT-Druid v3 represent the answer of Evidence Srl for the development of scalable real-time applications for AVR8.
ERIKA Enterprise v3 provides AVR8 developers the following features:
- Traditional RTOS features:
- Support for four conformance classes to match different application requirements;
- Support for preemptive and non-preemptive multitasking;
- Support for fixed priority scheduling;
- Support for stack sharing techniques, and one-shot task model to reduce the overall stack usage;
- Support for shared resources;
- Support for periodic activations using Alarms;
- Support for centralized Error Handling;
- Support for hook functions before and after each context switch.
- RT-Druid development environment
- Development environment based on the Eclipse IDE;
- Support for the OIL language for the specification of the RTOS configuration;
- Graphical configuration plugin to easily generate the OIL configuration file and to easily configure the RTOS parameters;
- Full integration with the Cygwin development environment to provide a Unix-style scripting environment;
- Apache ANT scripting support for code generation.
- AVR8 integration features
- Support for AVR8 GCC compiler;
- Support for the following families Atmel MCUs:
- Support for following boards
- Arduino Uno Board (ATmega328p)
- List of functions:
- Full support for Arduino SDK 1.8.5;
Integration with other tools for AVR8
ERIKA Enterprise and RT-Druid aims to the best integration with the existing tools for development available from the AVR microcontrollers. RT-Druid will be used to quickly configure the application, setting temporal parameters of real-time tasks, memory requirements, stack allocation and many other parameters. Moreover, RT-Druid generates the application template, and leaves the developer the task to implement the logic of each single task. While programming the application, the developer can exploit the power and flexibility offered by the primitives of the ERIKA Enterprise real-time kernel. ERIKA Enterprise also supports the compiling environments provided by Atmel, providing also direct support for the programming and JTAG solutions of Atmel.
Content of this document
The purpose of this document is to describe all the information needed to create, develop and modify an Erika Enterprise application for the AVR family of microcontrollers.
In particular, the document describes:
- The design flow which should be used to generate an Erika Enterprise application;
- The configuration of the development environment;
- The options which are available to configure the system.
As a final note, all the settings which are explained in this document apply both to Erika Enterprise if not otherwise stated.
Note: If you are looking for a step-by-step / quick guide tutorial on how to use Erika Enterprise and RT-Druid with AVR, please read the “Erika Enterprise Tutorial for the AVR microcontrollers”, available for download on the Evidence Web site.
Configuration and Programming
ERIKA Enterprise is configured through RT-Druid and an OIL file. Here are listed, after the information to set compiler path, the OIL fields customized for Atmel AVR8 architecture.
Compiler Path
It is possible to choose the path of the compiler in three different ways:
- PATH enviornment variable: You can put compilers bin directories in PATH and the environmet can use them from here.
- Compiler specific environment variables:
- AVR8 GCC toolchain: You can specify the compiler path for AVR8 GCC with the AVR_TOOLS.
- RT-Druid configuration file see RT-Druid configuration#Compiler paths:
- preference_avr8__path_for_gcc_compiler set GCC compiler path for AVR8
Here is an example of RT-Druid configuration file.
CPU
CPU_DATA must be set to AVR8.
Example of a CPU_DATA section:
CPU_DATA = AVR8 {
...
};
MCU
MCU_DATA supports for now the MEGA value only.
MODEL attribute of MCU_DATA supports for now the MEGA_328p value only.
MCU_DATA = MEGA {
MODEL = MEGA_328p;
};
BOARD
For now there is no NATIVE board support for AVR8 Architecture. The ONLY supported board is Arduino via Arduino SDK 1.8.5.
Interrupt Handling
Interrupt Handling is microcontroller dependent so for each supported Atmel AVR8 microcontroller family, the ISRs configuration of ERIKA Enterprise v3 is shown below.
MEGA Family
The MEGA family of AVR8 microcontrollers has an interrupt vector table which is stored in the flash memory. The lowest addresses of the interrupt vector table is allocated to the RESET and to the interrupt vectors. Interrupt handlers placed at lower addresses have higher hardware priorities than interrupt handlers placed at higher addresses so the PRIORITY attribute of the ISR object in the OIL is USELESS. The complete list of SOURCE entries is shown below.
-
RESET: External Pin, Power-on Reset, Brown-out Reset and Watchdog System Reset -
INT0: External Interrupt Request 0 -
INT1: External Interrupt Request 1 -
PCINT0: Pin Change Interrupt Request 0 -
PCINT1: Pin Change Interrupt Request 1 -
PCINT2: Pin Change Interrupt Request 2 -
WDT: Watchdog Time-out Interrupt -
TIMER2_COMPA: Timer/Counter2 Compare Match A -
TIMER2_COMPB: Timer/Counter2 Compare Match B -
TIMER2_OVF: Timer/Counter2 Overflow -
TIMER1_CAPT: Timer/Counter1 Capture Event -
TIMER1_COMPA: Timer/Counter1 Compare Match A -
TIMER1_COMPB: Timer/Coutner1 Compare Match B -
TIMER1_OVF: Timer/Counter1 Overflow -
TIMER0_COMPA: Timer/Counter0 Compare Match A -
TIMER0_COMPB: Timer/Counter0 Compare Match B -
TIMER0_OVF: Timer/Counter0 Overflow -
SPI_STC: SPI Serial Transfer Complete -
USART_RX: USART Rx Complete -
USART_UDRE: USART, Data Register Empty -
USART_TX: USART, Tx Complete -
ADC_ADC: Conversion Complete -
EE_READY: EEPROM Ready -
ANALOG_COMP: Analog Comparator -
TWI: 2-wire Serial Interface -
SPM_READY: Store Program Memory Ready
EEOPT
The following EEOPTs are specific of AVR8 Architecture:
- __AVR8_GCC_C99__: Enables C99 compiler option.
OSEK/VDX Extensions
This Section contains information about the OSEK/VDX Extensions (or optional features) that have been implemented for the AVR8 support.
System Timer
System Timer is microcontroller dependent so for each supported Atmel AVR8 microcontroller family, the System Timer configuration of ERIKA Enterprise v3 is shown below.
MEGA Family
For the MEGA family of AVR8 microcontrollers the System Timer is linked to TIMER1 so the DEVICE attribute MUST be se to TIMER1_COMPA as shown below.
COUNTER SystemTimer {
MINCYCLE = 1;
MAXALLOWEDVALUE = 65535;
TICKSPERBASE = 1;
TYPE = HARDWARE {
DEVICE = "TIMER1_COMPA";
SYSTEM_TIMER = TRUE;
};
SECONDSPERTICK = 0.001;
};
Additional Notes
T.B.D.
