03. Registers and memory

Supplemental: MIPS Assembly Language by Gary Shute

Convention: A set of terms on using architecture features in program. A convention can be broken by cost of (painful) incompatibility.

Registers

Alternate Name	Register Name	Use
$zero	$0	constant value 0
$s0 - $s8	$16 - $23, $30	saved values - preserved across calls
$sp	$29	stack pointer - preserved across calls
$ra	$31	return address - not preserved across calls
$a0 - $a3	$4 - $7	the first four parameters - not preserved across calls
$t0 - $t9	$8 - $15, $24 - $25	temporaries - not preserved across calls
$v0 - $v1	$2 - $3	expression evaluation and subprogram return value - not preserved across calls
$at	$1	reserved by the assembler - dangerous to use
$gp	$28	global pointer - dangerous to use
$k0 - $k1	$26 - $27	reserved by the operating system - dangerous to use

Flat memory model

Data placement directives

Directive	Operand Syntax	Meaning
.globl	label { , label }*	Declare labels to be global
.data	none	Start a data declaration section
.text	none	Start an instruction section
.word	integer [ : non-negative integer ]	Declare a C int variable
.asciiz	string	Declare a string variable
.align	number	Align next address by 2**number bytes

Code addressing

strict %4
i-commands (branch) and j-command (jump)
two-bit cropping

E. g. (beware of meaningless code):

   1 .text
   2         li      $t0, 20
   3 start:  li      $t1, 5
   4         move    $t2, $t0
   5 loop:   beqz    $t2, fin
   6         subu    $t2, $t2, $t1
   7         b       loop
   8 fin:    sra     $t0, $t0, 1
   9         bnez    $t0, end
  10         j       start
  11 end:    nop

H/W

EJudge: DoubleSum 'Double sum'

Enter four integers, one in line, and add uniconditionally first one to third one, and second one to fourth one. Print results in two lines.
Input:
```
234
-23
23
64
```
Output:
```
257
41
```

HSE/ArchitectureASM/03_RegistersMemory (последним исправлял пользователь FrBrGeorge 2019-11-22 13:59:35)