<< Chapter < Page Chapter >> Page >

Then, why didn't the designer of the CPU make such that LDW instruction takes 5 clock cycles to begin with, rather than let the programmer insert 4 NOPs ? The answer is that you can insert other instructions other than NOPs as far as those instructions do not use the result of the LDW instruction above. By doing this, the CPU can execute additional instructions while waiting for the result of the LDW instruction to be valid, greatly reducing the total execution time of the entire program.

More on instructions with delay slots

The Table 3-5 in TI's instruction set description shows the execution of the instructions with delay slots in moredetail. The instructions with delay slots are multiply ( MPY , 1 delay slot), the load ( LDB, LDW etc. 4 delay slots) instructions, and the branch ( B , 5 delay slots) instruction.

The functional unit latency indicates for how many clock cycles each instructions actually use afunctional unit. All C62x instructions have 1 functionalunit latency, meaning that each functional unit is ready to execute the next instruction after 1 clock cycle regardlessof the delay slots of the instructions. Therefore, the following instructions are valid:

1 LDW .D1 *A10, A4 2 ADD .D1 A1,A2,A3

Although the first LDW instruction do not load the A4 register correctly while the ADD is executed, the D1 functional unit becomes available in the clock cycle right after the one in which LDW is executed.

To clarify the execution of instructions with delay slots, let's think of the following example of LDW instruction. Let's assume A10 = 0x0100 A2=1 , and your intent is loading A9 with the 32-bit word at the address 0x0104 . The 3 MV instructions are not related to the LDW instruction. They do something else.

1 LDW .D1 *A10++[A2], A92 MV .L1 A10, A8 3 MV .L1 A1, A104 MV .L1 A1, A2 5 ...

We can ask several interesting questions at this point:

  • What is the value loaded to A8 ? That is, in which clock cycle, the address pointer isupdated?
  • Can we load the address offset register A2 before the LDW instruction finishes the actual loading?
  • Is it legal to load to A10 before the first LDW finishes loading the memory content to A9 ? That is, can we change the address pointer before the 4 delay slotselapse?
Here are the answers:
  • Although it takes extra 4 clock cycles for the LDW instruction to load the memory content to A9 , the address pointer and offset registers ( A10 and A2 ) are read and updated in the clock cycle the LDW instruction is issued. Therefore, in line 2, A8 is loaded with the updated A10 , that is A10 = A8 = 0x104 .
  • Because the LDW reads the A10 and A2 registers in the first clock cycle, you are free to change these registers and do not affect the operationof the first LDW .
  • This was already answered above.

Similar theory holds for MPY and B (when using a register as a branch address) instructions. The MPY reads in the source values in the first clock cycle and loads themultiplication result after the 2nd clock cycle. For B , the address pointer is read in the first clock cycle, and the actual branching occurs after the5th clock cycle. Thus, after the first clock cycle, you are free to modify the source or the address pointer registers.For more details, refer Table 3-5 in the instruction set description or read the description of the individualinstruction.

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
Nasa has use it in the 60's, copper as water purification in the moon travel.
nanocopper obvius
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
analytical skills graphene is prepared to kill any type viruses .
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
where are the solutions?
where are the solutions?

Get the best Algebra and trigonometry course in your pocket!

Source:  OpenStax, Finite impulse response. OpenStax CNX. Feb 16, 2004 Download for free at http://cnx.org/content/col10226/1.1
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Finite impulse response' conversation and receive update notifications?