- Fact
(from lecture):
- Registers in a CPU are
used to perform computations
- In CS255, we only studied integer typed computations (for simplicity)
- The ARM CPU can perform
computations on
3 different kinds of
integer values:
- byte size integers (whole numbers represented using 8 bits)
- short size integers (whole numbers represented using 16 bits)
- int size integers (whole numbers represented using 32 bits)
- There are 2 different representation
of whole values used in
the computer:
- Signed integer (whole value)
- Unsigned integer (whole value)
- The integer values are
represented in binary inside
the computer
For humans, we like to read (= see) the values in decimal representation
Notice that:
- All values stored in
a register are stored as
a binary number
- Depending on the kind of value stored in the register, you must apply a different decoding method to interpret the value stored in the register !!!
Because of the many different decoding method that you need to use, EGTAPI has provide many display options to show (= decode) the binary representation in a register.
- Next to General Purpose Register
(which also include the special purpose registers),
you will
find an arrow (drop down menu)
that you can
click to
select the
display option for
the value stored in the
register:
Click on the arrow to select a display option
If you want to save the display options that you have set, click on the Save Displ button next to the PC/PSR registers
- Registers in a CPU are
used to perform computations
- The 32 bits value stored in
a data/address register can
be displayed in
any of the
following
ways:
- As one 32 bit binary number
- To display the value in the
register as
a 32 bit binary number,
select
the B (= binary) display option:
- To display the value in the
register as
a 32 bit binary number,
select
the B (= binary) display option:
- As one 32 bits unsigned decimal (integer)
number
- To display the value in the
register as
a
32 bit signed deciaml number,
select
the D UI (= decimal -
unsigned int)
display option:
Notice that: the 32 bits 11111111 11111111 11111111 11111101 (stored in register D0) interpreted using the binary number system (for converting binary to unsigned integers), represents the decimal value 231 + 230 + ... + 23 + 22 + 20 = 4294967293
- To display the value in the
register as
a
32 bit signed deciaml number,
select
the D UI (= decimal -
unsigned int)
display option:
- As one 32 bits signed decimal (integer)
number
- To display the value in the
register as
a
32 bit signed deciaml number,
select
the D SI (= decimal - signed int)
display option:
Notice that: the 32 bits 11111111 11111111 11111111 11111101 (stored in register D0) interpreted using the 2's complement number system (for converting binary to signed integers), represents the negative decimal value of 00000000 00000000 00000000 00000011 = 3
- To display the value in the
register as
a
32 bit signed deciaml number,
select
the D SI (= decimal - signed int)
display option:
- As two
16 bits unsigned decimal (integer)
number
- To display the value in the
register as
two
16 bits unsigned deciaml number,
select
the D US (= decimal -
unsigned short)
display option:
Notice that: the first 16 bits 11111111 11111111 in register D0 interpreted using the binary number system, represents the decimal value of 215 + 214 + ... + 22 + 21 + 20 = 65535
The second 16 bits 11111111 11111101 in register D0 interpreted using the 2's complement number system, represents the negative decimal value of 215 + 214 + ... + 22 + 20 = 65533
- To display the value in the
register as
two
16 bits unsigned deciaml number,
select
the D US (= decimal -
unsigned short)
display option:
- As two
16 bits signed decimal (integer)
number
- To display the value in the
register as
two
16 bits signed deciaml number,
select
the D SS (= decimal -
signed short)
display option:
Notice that: the first 16 bits 11111111 11111111 in register D0 interpreted using the 2's complement number system, represents the negative decimal value of 00000000 00000001 = 1
The second 16 bits 11111111 11111101 in register D0 interpreted using the 2's complement number system, represents the negative decimal value of 00000000 00000011 = 3
- To display the value in the
register as
two
16 bits signed deciaml number,
select
the D SS (= decimal -
signed short)
display option:
- As four
8 bits unsigned decimal (integer)
number
- To display the value in the
register as
four
8 bits unsigned deciaml number,
select
the D UB (= decimal -
unsigned byte)
display option:
- To display the value in the
register as
four
8 bits unsigned deciaml number,
select
the D UB (= decimal -
unsigned byte)
display option:
- As four
8 bits signed decimal (integer)
number
- To display the value in the
register as
four
8 bits signed deciaml number,
select
the D SB (= decimal -
signed byte)
display option:
- To display the value in the
register as
four
8 bits signed deciaml number,
select
the D SB (= decimal -
signed byte)
display option:
- As a
32 bits IEEE 754 (floating point)
number
- To display the value in the register as four 32 bits floating point number, select the float display option.
- As one 32 bit binary number
Comment:
- You can
also display the value in the
hexa-decimal number system:
- Select the H option
- Under the hexa-decimal
display menu, you can display
the 32 bits stored in a
register as:
- One 32 bits representation (H UI)
- Two 16 bits representation (H US) or
- Four 8 bits representation (H UB)
Only the unsigned representation in hexadecimal is supported in EGTAPI
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