FIFO memory buffers!!!

There are many serial communicating devices which gives data in bursts, i.e after launching several data in consecutive cycles, it then becomes quite for several cycles. 

And in some other cases the frequency of such operations are different, where the device and processor will be on different clocks.
This causes Data Loss.

How to prevent this Data Loss?

A FIFO is a special type of buffer, where data written into the buffer first comes out first. There are other kinds of buffers, and choice of buffer is architecture dependent.

FIFOs can be implemented with software or hardware. The choice between a software and a hardware solution depends on the type of application and features desired.

How it works?

There are two clocks involved, a launch clock during which the data is stored in the FIFO just like write clock, and a capture clock where the data is read from the FIFO like read clock.

In a circular FIFO concept, the memory address of the incoming data is in the write pointer. The address of the first data word in the FIFO that is to be read out is in the read pointer. After reset, both pointers indicate the same memory location. After each write operation, the write pointer is set to the next memory location. The reading of a data word sets the read pointer to the next data word that is to be read out. The read pointer constantly follows the write pointer. When the read pointer reaches the write pointer, the FIFO is EMPTY. If the write pointer catches up with the read pointer, the FIFO is FULL.

FIFO Limitations:

FIFO is not of much use if launch clock is faster than capture clock, and if average data rate is greater than capture rate, because after a while, the FIFO would become FULL.

How to decide of FIFO buffer Size?

FIFO depth is decided as :

(data bytes (burst) written in write clock) - (data bytes read in read clock in the time taken to write the burst).

Example: Suppose 200 bytes burst is to be written at 100 MHZ, 1 byte per write clock. and Read clock is 50 MHZ, 1 byte read per read clock. what is the FIFO depth?

Time taken to write 1 byte = (1/100) = 10 ns
So, Time taken to write 200 Bytes = 10 * 200 = 2000 ns

Time required to read 1 byte = (1/50) = 20 ns
So, in 2000 ns date bytes read = (2000/20) = 100 Bytes

So, FIFO Depth = 200 - 100 = 100 Bytes.

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What is digital datapath?

A datapath is a collection of functional units, such as arithmetic logic units or multipliers, that perform data processing operations.

Datapath elements include adders, multipliers, shifters, BFUs, etc.

• The speed of these elements often dominates the overall system performance so optimization techniques are important.

 

• However, as we will see, the task is non-trivial since there are multiple equivalent logic and circuit topologies to choose from, each with adv./disadv. in terms of speed, power and area.

 

• Also, optimizations focused at one design level, e.g., sizing transistors, leads to inferior designs. 

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Soft Core Processors

Due to growth in use of FPGA and ASIC, the design of specific hardware units reduced. Application specific processors which are not needed for other applications are designed on these Configurable ICs.

As logic in these ICs are implemented using HDL synthesis. The implementation of a specific microprocessor is carried out in way, where a specific hardware of the mu-p is not developed rather it is built on an available configurable logic platform.

Soft-core processors are microprocessors whose architecture and behaviour are fully described using hardware description language (HDL).

Some common soft core processors used are: Nios II by Altera, MicroBlaze from Xilinx, LEON by Gaisler Research, OpenRISC 1200.

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What is Backward Compatibility?

In telecommunications and computing, a product or technology is backward or downward compatible if it can work with older product or technology. If products designed for the new standard can receive, read, view or play older standards or formats, then the product is said to be backward-compatible.

For example if Intel i7 can run programs designed for Intel Core 2 Duo such a product is backward compatible.

The reverse is forward compatibility, which implies that old devices allow (or expected to allow) data formats generated by new (or future) devices, perhaps without supporting all new features. A standard supports forward compatibility if older product versions can receive, read, view, or play the new standard.

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Resistors, Capacitors, Inductors

Resistors

RESIST - according to English dictionary means "withstand the action or effect of something". Resistors in electronics it is withstand the action or effect of electrons.

Resistor is the most commonly used passive component which limit the current by lowering voltage levels.

Resistance is the amount of action or effect of electrons, resistors can withstand. It is measured in ohms(Ω), which is its SI unit named after George Simon Ohm.

(Conductance is opposite of resistance).

Many types of resistors are available, some prominent types are:

1. Carbon composition resistors - Graphite material in it forms resistive element. 
2. Metal film resistors - The metal film determines resistance. 
3. Wire wound resistors - Metal wire(nichrome usually) is the resistive material.
4. Potentiometers - which have varying resistivity.

 The power from resistors is dissipated due to current flow. This dissipation is usually in the form of heat.

Capacitors

Capacitor as its name stands, it is the capacity of the device to store energy. It stores energy in terms of electric field. Unlike resistors, capacitors doesn't dissipate energy, instead stores it.

Capacitance is a measure of the amount of energy it can store. It is measured in farads(f).

Many types of capacitors are available, most commonly used are:

• Parallel plate
• Ceramic
• Electrolytic

 

Inductors

Another most commonly used passive device. An inductor is also a coli, which resist change in current flow. Due to current flow in coil there is magnetic field due to it. This magnetic filed oppose sudden change in current flowing through the coil.

Inductance gives the measure of the opposition it offers to the change in current. It is measured in Henries(H).

Some types of Inductors are:

•  Air Core Inductor 
• RF Inductor
• Ferromagnetic Core Inductor
• Ferrite Core Inductor

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