- Recall my
mechanical representation of
a (electrical) computer:
A computer can only execute 3 categories (kinds) of instructions:
- Data copying operations:
- Some data is
transfered (copied) from
a source location to
a destination location
There are 3 ways of data transfer:
- Move data: the data is copied from a register to another register inside the CPU
- Load data: the data is copied from a memory location to a register inside the CPU
- Store data: the data is copied from a register inside the CPU to a memory location
- Some data is
transfered (copied) from
a source location to
a destination location
- Arithmetic/logical operations:
- Values from 1 or 2 source (general purpose) registers (inside the CPU) are combined (e.g., negation, add, subtract, multiply, etc) and the result of operation is stored in a destination (general purpose) register
- Branch
operations:
(with or without linking)
- The Program Counter is
updated by
the computer instruction
- Because the CPU will fetch the next instruction from memory at the address given by the value in the Program Counter, updating the Program Counter will cause the CPU to fetch the next instruction at a new location !!!
- A branch operation will therefore make the program jump to a different part of the program and continues the program execution at the branch address given in the branch instruction
- The Program Counter is
updated by
the computer instruction
- Data copying operations:
- Comment:
- Some computers has
instructions that
combine
2 (or more) kinds of above
basic instructions
Example:
- Intel processors can
execute arithmetic operations
on a value stored in
memory
This type of instruction is performed by combining 3 basic operations:
- First, the CPU transfer the data from memory into a scratch register(s) inside the ALU
- Then, the CPU performs the Arithmetic/logic operation using values in the scratch register(s) and store the result in (another) register
- Finally, the CPU transfer the result in the register to the memory using another data copying operation
A processer provides combined operations (such as the Intel processor) for the convience of the assembler programmer
- Intel processors can
execute arithmetic operations
on a value stored in
memory
- Some computers has
instructions that
combine
2 (or more) kinds of above
basic instructions
- A list of all possible
instructions
of the ARM processor
(ARM is used in many tablet devices):
- The page 1 of this
PDF file contains
all the possible instruction of
the ARM processor that
we use in CS255:
click here
- If you go through the
types of
instructions in
column 1 of the PDF file,
you will see that
the ARM processor
(used in most tablet devices)
can only execute these
types of
instructions:
Move - this is a copy instruction (item 1 in my list above) Arithmetic - in my list as item 2 Logical - in my list as item 2 Compare - in my list as item 2 Branch - in my list as item 3 Load - this is a copy instruction using a memory cell as data source and a register as destination (item 1 in my list) Store - this is a copy instruction using a register as data source and a memory cell as destination (item 1 in my list) Load Multiple - executes multiple Load instructions for user's convenience Store Multiple - executes multiple Store instructions for user's convenience
So you see that every instruction of the very popular ARM processor (used in many table devices) fall in the 3 categorizes of instructions
- The page 1 of this
PDF file contains
all the possible instruction of
the ARM processor that
we use in CS255:
click here