Memory Organisation in embedded systems
- 1. Lecture 1 MEMORY ORGANISATION IN EMBEDDED SYSTEMS
- 2. Memory 1. Memory is an important component in an embedded system as it stores all and any form of data depending upon its design architecture. 2. For anyone to learn and have a deeper knowledge of the embedded systems, it's important that one should first understand what the memory of their hardware can actually offer or how one can design the hardware for their application . 3. In data centers, they deal with Petabytes of memory. In personal computers, they deal with mega->terabytes size of memory, But when it comes to embedded systems ,it's usually from kiloBytes to megaBytes of memory. 4. So, It is important that we understand,utilise and optimise this small amount of memory efficiently in embedded systems.
- 3. Types of Memory Lorem Ipsum MEMORY RAM - Volatile memory SRAM DRAM SDRAM Register PROM EPROM EEPROM Flash ROM - NonVolatile memory Volatile memory : Loses data once the power is turned off. Non- volatile memory : Retains data on losing power.
- 4. Transformation of ROM ROM is a non-volatile memory, meaning the data stored in ROM stays even after the power is turned off, having said so ROM also has endurance issues that data cannot be written over and over again, it has got limited number of write erase cycles before failure. ROM PROM EEPROM EPROM Flash ROM and PROM are programmed only once by the manufacturer and remains unchanged. EPROM are programmable multiple times and can be erased by exposing the memory to UV (ultra-violet)light. The next in the evolution comes the EEPROM and FLash which are electrically erasable and programmable ROM but Flash comes with an endurance issue (10,000 - 1,00,000+ write erase cycles)
- 5. RAM (Random access memory): RAM is a volatile memory (Ram requires constant electrical power to store Data and if the power is turned off then the data is erased.) and as the name suggests allows access to any part of the memory given the address of that location. 1. In order for Data or program to run on a computer. First, It needs to be loaded into RAM. 2. So, RAM basically stores the data of your current running programs. For eg, if you have opened your MS office document ,the MS word program will be copied to RAM and that’s when we get the loading symbol in the front when the program gets copied in the background. 3. Once the program is loaded in the RAM, the CPU can now run the program and access the data. The data that you keep feeding to your document will be saved to your RAM before you SAVE it with the command File->Save As to your respective drive folder of ROM memory. 4. So, RAM is a very convenient type of memory to hold data that keeps changing continuously. 5. More space in RAM allows the user to use more applications simultaneously and efficiently.
- 6. Types Of RAM : DRAM , SRAM, SDRAM 1. A DRAM uses a transistor - capacitor circuit to hold a bit of data. Charged state is 1 bit and discharged state is 0 bit. 2. While using capacitor, there may be leakage of current in capacitor due to the little amount of current that may be drawn by the adjacent transistor or just due to the inner behaviour of the capacitor itself. 3. So, the circuit needs to be refreshed with voltage continuously and will not work without power. 4. The data transfer is slow compared to SRAM and the cost is comparatively low. SDRAM is a synchronous DRAM where the instructions are synchronised with the clock speed of the microprocessor.
- 7. SRAM on the other hand works much faster than DRAM as it doesn’t have any capacitor in its circuit and 2 cross coupled transistors i.e 4 transistors for storing the charge and 2 transistors for access control. SRAM is much costlier and works very fast.
- 8. Register memory Registers are small memory that are present inside the processor itself. They contain the data of operands and instructions of a program that CPU is currently processing. Since registers are inside the processor, the time required to fetch data is very fast, but it cannot hold large data like RAM or ROM. It can hold only in bit levels. INTEL 8085 has popular 8-bit registers. ARM architecture has 32 bit registers. Registers also hold the peripheral address in microcontroller.
- 9. So far, In the ppt we have learnt about the volatile and non volatile memories of a computer. To make the understanding much better let us site an Analogy. The core memory of a computer , ie the ROM or HDD can be imagined to a library , where numerous books on various topics are stacked up neatly each one labelled. The matrix of books arranged is the ROM. The labels on each book can be imagined as memory addresses of each byte. Memory Analogy
- 10. And now consider yourself to be the CPU. Your task is to look for data to prepare for a science quiz. So, you have collected all the related books and placed them on the table top, which is the RAM. Now, More the table space, more books can be accommodated. This helps in fetching more data and saves time in going back to the shelf searching for the book and again coming back to the table. This is analogous to having more RAM size, when the program from the ROM is copied entirely to the RAM , the processor need not go back and forth to fetch data and instruction from the ROM as everything is copied to RAM and the execution is much faster.
- 11. When you start the process, you will start reading the index of the book , memorize the page number and go to the particular page looking for information. This is similar to saving the page number data to the register memory and performing the next task. When you want to search the meaning of a particular word. You memorize the word in your head and take another book from the table top to know the meaning of it. This is similar to saving the address data in register memory and looking for the data in that address in RAM. Once the work is complete, all the books on the table will go back to the shelf and this is similar to RAM data dissolving once the power is out. And once you come out your memory will eventually forget the trivial data of page number and others. But some important data, like word- meaning might stay in your head for a long time then sync that to cache memory of the CPU.
- 12. Thank You Hope you would have gained a good knowledge about memory and a overview of how it works inside the computer