Advanced Embedded Systems Interview Preparation Guide

☛ Data pointer register is used in the indexed addressing mode.
☛ It is used in accessing data from tne look-up table entries stored in ROM.
☛ SYNTAX: MOVC A, @A+DPTR
☛ Here c means the code (shows data elements are stored in code space of ROM).
☛ The contents of A are added to 16 bit DPTR to form the 16 bit address of the needed data.

☛ The microcontroller & processor can be interchangeably used here.
☛ It forms a general purpose processor .
☛ High-end stands for system of greatest power.
☛ Here when a microcontroller cannot do a specific task the processor does the same with higher power
☛ Example: ADM 64

☛ The general purpose registers named A,B, R0-R7 can not accept the immediate data.
☛ To indicate immediate value pound sign is used before it.
☛ These register accept 8 bit data preceding a pound sign.
☛ There are registers present in 8051 used to store data temporarily.

The ‘A’ register called the accumulator is used as the destination register.
Example:
ADD R2, # 12H
This is invalid as 12 is to be added to value present in R2 and data is also stored in R2.
ADD A,# 12H
This is valid as 12 is to be added to the value present in accumulator. Foregoing discussion explains why register A is used as accumulator.
Explain LCALL.

☛ It is called long call and is a 3 byte instruction.
☛ Here 1st byte is used for opcode &2nd & 3rd bytes are used for address of target subroutine.
☛ Call subroutine can be used anywhere within 64 K- byte address space.
☛ Processor automatically saves on stack the address of instruction immediately below LCALL.
☛ After execution instruction return (RET) transfers control back to next instruction.

☛ The amount of code that has to be dealt with is reduced thus easing the overhead and redundancy is eliminated in case if there is anything common among the functions.

☛ Memory allocation is another aspect that is optimized and it also makes sense to group a set of functions related in some way as one single unit rather than having them to be dispersed in the whole program.

☛ In case of interactive systems display of menu list and reading in the choices of user's could be encapsulated as a single unit.

☛ Analytical model allows the components to deal with the concurrency that are given during the process and the quantitative constraints that might come in between the components. Whereas, computational model deal with the non-deterministic abstraction hierarchy that has computational complexity to deal with the concurrency and allow it put also the physical constraints.

☛ Analytical models can’t deal with the partial and incremental specifications that are non-deterministic. It is also not good in controlling the computation complexity that is used in the hardware design. Whereas, Computational model can, deal with constraints easily and it provides an upgradeable solution.

☛ Analytical model is the equation based model that doesn’t have the time-sharing and parallelism concepts. Whereas, time-sharing and parallelism is used, in the abstract method that provides the theories of complexity and the real time evaluation.

The memory bus is used to carry the address and the data from the processor to the memory so that it can be easily accessed by the devices. These buses carry the value of the data that has to be passed for the proper functioning. The use of the technique “Time division multiplexing” is used that allow the reading and writing of the data to be done from the same bus line. This requires lots of time to be given to the bus so that it can complete the read and write operation of the data in the memory. This is very expensive process due to the data transfer technique that is used in between the processor and the memory. This also gives the concept of cache and provides algorithms to solve the problems occurring in read and writes operations.

DMA stands for Direct Memory Access controller that handles the allocation of the memory dynamically to the components and allows the data to be transferred between the devices. It is used for the communication between different input/output devices. It automatically detects the devices that are present for the transfer of data between the input/output devices. The interrupt can be used to complete the data transfer between the devices. It is used to give the high quality performance as, the input/output device can perform the operations that are in parallel with the code that are in execution phase. It can’t be used in all the systems. It consists of 8-bit microcontrollers that are used to control the overall system in execution.

Critical section allows the process to run in an area that is defined by that process only. It is a sequence of instructions that can be corrupted if any other process tries to interrupt it. This process allow the operating system to give the synchronization objects that are used to monitor the processes that are up and running so that no other process will get executed till the critical region consists of a process that is already running. The example includes removal of the data from a queue running in a critical section and if not protected then it can be interrupted and the data have chances of getting corrupted. The processes exit from the critical section as soon as they finish the execution so that the chances can be given to other processes that are waiting for their chance to come.

☛ DB is called as define byte used as a directive in the assembler.
☛ It is used to define the 8 bit data in binary ,hexadecimal or decimal formats.
☛ It is the only directive that can be used to define ASCII strings larger than two characters.
☛ DB is also used to allocate memory in byte sized chunks.
☛ The assembler always converts the numbers lnto hexadecimal.