Advanced Embedded Systems

Interrupt architecture allows the use of interrupt by the processor whenever an Input/output is ready for the processing. The processor in this case calls a special function to handle the request that comes and leave all the work that is getting performed at that time. The special function that is known as interrupt handler or the interrupt service routine consists of all the input, and output queries, or the interrupts handled by it. It is an efficient and simple way to handle the interrupts. It uses only one function to deal with the interrupts. There are properties of starvation that can creep in when handling the input/output requests. The data can be lost if the interrupt doesn’t get handled before the time runs out. This is a technique that is use to deal with the short processes that involve input and output.

☛ According to the instruction sets used, computers are normally classified into RISC and CISC. RISC stands for 'Reduced Instruction Set Computing' . The design philosophy of RISC architecture is such that only one instruction is performed on each machine cycle thus taking very less time and speeding up when compared to their CISC counterparts.

☛ Here the use of registers is optimised as most of the memory access operations are limited to store and load operations.

☛ Fewer and simple addressing modes, and simple instruction formats leads to greater efficiency, optimisation of compilers, re-organisation of code for better throughput in terms of space and time complexities. All these features make it the choice of architecture in majority of the Embedded systems.

☛ CISC again have their own advantages and they are preferred whenever the performance and compiler simplification are the issues to be taken care of.

Multi-threading allows a simple thread to be stored and polled. There is no Input/output function that is applied when it is having the poll. When there is no poll available to spawn it makes the system to sleep for an amount of time till the request for another poll reaches. If there is one process that is running then it divides that process into multiple threads and processes it accordingly. It allows the main thread to process all the request and produce the output by combining all other. Multi-threading allows the main thread not to put off the result or the output that will be generated. It also allow the priority of the thread to be changed by allowing to set the priority of the input/output process. It also has some problems with the polling interval that can make a thread starve for some time if the request isn’t handled properly.

Multi-threading provide lot of functionality to the system to allow more than one task can be run at a time. It allows a process to execute faster with less difficulty. But, if there any problem comes in any program or the process than the entire system comes to a halt and slows down the whole system. To control the behavior of this the preemptive multi-threading is used. The control in this case is being shifted from one process to another at any time according to the requirement provided. It allows the program to give the control to another program that is having the higher priority. It includes of many problems like giving of a control by a process half way through in execution and the preemption of the process takes place then the data will be entered as corrupted in the memory location, multi-threading keeps the synchronization that is to be performed between different components of the system and the program and try to avoid the problem mentioned above.

Device drivers are basically a set of modules/routines so as to handle a device for which a direct way of communication is not possible through the user's application program and these can be thought of as an interface thus keeping the system small providing for minimalistic of additions of code, if any.

Physical device drivers can’t perform all the logical operations needed in a system in cases like IPC, Signals and so on...

The main reason for having virtual device drivers is to mimic the behaviour of certain hardware devices without it actually being present and these could be attributed to the high cost of the devices or the unavailability of such devices.

These basically create an illusion for the users as if they are using the actual hardware and enable them to carryout their simulation results.

Examples could be the use of virtual drivers in case of Network simulators,also the support of virtual device drivers in case a user runs an additional OS in a virtual box kind of a software.

☛ Endianness basically refers to the ordering of the bytes within words or larger bytes of data treated as a single entity.

☛ When we consider a several bytes of data say for instance 4 bytes of data,XYZQ the lower byte if stored in a Higher address and others in successively decreasing addresses, then it refers to the Big Endian and the vice versa of this refers to Little Endian architecture.

☛ Intel 80x86 usually follows Little Endian and others like IBM systems follow Big Endian formats.

☛ If the data is being transmitted care has to be taken so as to know as to which byte,whether the higher or the lower byte is being transmitted.

☛ Hence a common format prior to communication has to be agreed upon to avoid wrong interpretation/calculations.

☛ Usually layer modules are written so as to automate these conversion in Operating systems.

Volatile keyword is used to show that the value can be changed anytime in the program. It is used for the compiler purpose and for the customization that works with the normal variables that are stored in the memory. There are three types of optimizations associated with the “volatile” keyword:

☛ "Read" optimizations: allow the variable to be read once and put it in the register. If it is done then there is no re-reading of the variable during each and every time the program is compiled. The value can be used from the cache that is present in the register.

☛ "Write" optimizations: allow the variable to be written such that the last write of the variable will be considered and it will be processed on. This takes the normal values that are stored in the memory.

☛ Instruction reordering: allow to reorder the instructions that are used by the compiler and if any modification are required after being written once. The registers are used to perform the task and keep everything together.

Mutex is also called as Mutual Exclusion is a mechanism that is used to show the preemptive environment and allow providing security methods like preventing an unauthorized access to the resources that are getting used in the system. There are several rules that has to be followed to ensure the security policies:

☛ Mutex are directly managed by the system kernel that provides a secure environment to allow only the applications that passes the security rules and regulations. The mutex consists of objects that are allowed to be called by the kernel.

☛ Mutex can have only one process at a time in its area that is owned by the process using it. This allows less conflict between the different applications or processes that wait for their turn to execute it in the kernel area.

☛ Mutex can be allocated to another mutex that is running some task at a particular time and allow the kernel to have synchronization in between them.

☛ If Mutex is allocated to some other process then the area will consist of the process till the area is having the process in it.