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Ecalls

Jupiter currently supports a total of 26 environment calls through ecall instruction. To use an environment call, load the ecall code into register a0 and load any arguments into a1 - a7 or fa0-fa7 (floating-point) registers.

Print Int

Prints integer in register a1.

Example

.globl __start

.text

__start:
  li a0, 1   # ecall code
  li a1, 0xa # integer to print
  ecall

Ecall Code

  • a0 = 1

Arguments

  • a1 = integer to print

Print Float

Prints float in register fa0.

Example

.globl __start

.rodata

  PI: .float 3.1416

.text

__start:
  li a0, 2        # ecall code
  la t0, PI
  flw fa0, 0(t0)  # float to print
  ecall

Ecall Code

  • a0 = 2

Arguments

  • fa0 = float to print

Print String

Prints null-terminated string whose address is in register a1.

Example

.globl __start

.rodata

  msg: .asciiz "Hello World!!!"

.text

__start:
  li a0, 4   # ecall code
  la a1, msg # string to print
  ecall

Ecall Code

  • a0 = 4

Arguments

  • a1 = null-terminated string address

Read Int

Reads an integer from stdin and stores the result in register a0.

Example

.globl __start

.text

__start:
  li a0, 5 # ecall code
  ecall

Ecall Code

  • a0 = 5

Arguments

  • none

Read Float

Reads a float from stdin and stores the result in register fa0.

Example

.globl __start

.text

__start:
  li a0, 6 # ecall code
  ecall

Ecall Code

  • a0 = 6

Arguments

  • none

Read String

It reads up to length - 1 characters into a buffer whose address is in a1 and terminates the string with a null byte. Buffer size has to be at least length bytes.

Example

.globl __start

.data
  string: .zero 256 # buffer with len = 256

.text

__start:
  li a0, 8      # ecall code
  la a1, string # buffer address
  li a2, 256    # length
  ecall

Ecall Code

  • a0 = 8

Arguments

  • a1 = buffer address

  • a2 = buffer length

Sbrk

Stores a pointer to a block of memory containing n additional bytes in register a0. This pointer is word aligned.

Example

.globl __start

.text

__start:
  li a0, 9   # ecall code
  li a1, 100 # number of bytes
  ecall

Ecall Code

  • a0 = 9

Arguments

  • a1 = number of bytes to reserve

Exit

Stops a program from running.

Example

.globl __start

.text

__start:
  li a0, 10 # ecall code
  ecall

Ecall Code

  • a0 = 10

Arguments

  • none

Print Char

Prints a character whose ascii code is in register a1.

Example

.globl __start

.text

__start:
  li a0, 11  # ecall code
  li a1, 'a' # character to print
  ecall

Ecall Code

  • a0 = 11

Arguments

  • a1 = ascii code to print

Read Char

Reads a character from stdin and stores the ascii code in register a0.

Example

.globl __start

.text

__start:
  li a0, 12 # ecall code
  ecall

Ecall Code

  • a0 = 12

Arguments

  • none

Open

Opens a new file and obtains its file descriptor. Stores the file descriptor for the new file in register a0. The file descriptor returned is always the smallest integer greater than zero that is still available. If a negative value is returned, then there was an error opening the file. Maximum number of open files: 32.

Example

.globl __start

.rodata
  # open flags
  O_RDWR:  .word 0b0000100
  O_CREAT: .word 0b0100000
  O_EXCL:  .word 0b1000000
  # pathname
  path: "example.txt"

.text

__start:
  li a0, 13      # ecall code
  la a1, path    # pathname address
  lw a2, O_RDWR  # load O_RDWR open flag
  lw t0, O_CREAT # load O_CREAT open flag
  lw t1, O_EXCL  # load O_EXCL open flag
  or a2, a2, t0  # set a2 = O_RDWR | O_CREAT
  or a2, a2, t1  # set a2 = O_RDWR | O_CREAT | O_EXCL
  ecall

Ecall Code

  • a0 = 13

Arguments

  • a1 = pathname address

  • a2 = open flags

Open Flags

Name

Code

Description

O_RDONLY

0b0000001

Open the file so that it is read only

O_WRONLY

0b0000010

Open the file so that it is write only

O_RDWR

0b0000100

Open the file so that it can be read from and written to

O_APPEND

0b0001000

Append new information to the end of the file

O_TRUNC

0b0010000

Initially clear all data from the file

O_CREAT

0b0100000

If the file does not exist, create it

O_EXCL

0b1000000

Combined with the O_CREAT option, it ensures that the caller must create the file. If file already exists, the call will fail

Read

Reads data into a buffer whose address is in register a2. Stores the number of bytes that were read in register a0. If value is negative, then an error occurred. The buffer size should be greater or equal to the number bytes to read.

Example

.globl __start

.data
  read: .zero 1024

.text

__start:
  li a0, 14   # ecall code
  li a1, 1    # file descriptor
  la a2, read # buffer address
  li a3, 10   # number of bytes to read
  ecall

Ecall Code

  • a0 = 14

Arguments

  • a1 = file descriptor

  • a2 = buffer address

  • a3 = number of bytes to read

Write

Writes data out of a buffer whose address is in register a2. Stores the number of bytes that were written in register a0. If value is negative, then an error occurred.

Example

.globl main

.data
  write: .asciiz "Hello World"

.text

main:
  li a0, 15    # ecall code
  li a1, 1     # file descriptor
  la a2, write # buffer address
  li a3, 12    # number of bytes to write
  ecall

Ecall Code

  • a0 = 15

Arguments

  • a1 = file descriptor

  • a2 = buffer address

  • a3 = number of bytes to write

Close

Close an open file descriptor. Stores a 0 upon success in register a0, and a -1 upon failure.

Example

.globl __start

.text

__start:
  li a0, 16 # ecall code
  li a1, 1  # file descriptor
  ecall

Ecall Code

  • a0 = 16

Arguments

  • a1 = file descriptor

Exit2

Stops the program from running and takes an argument, which is the value that Jupiter uses in its call on exit.

Example

.globl __start

.text

__start:
  li a0, 17 # ecall code
  li a1, 1  # status code value
  ecall

Ecall Code

  • a0 = 17

Arguments

  • a1 = exit status code

Lseek

Changes the location of the read/write pointer of a file descriptor. The location can be set either in absolute or relative terms.

Example

.globl __start


__start:
  li a0, 10
  ecall

Ecall Code

  • a0 = 18

Arguments

  • a1 = file descriptor

  • a2 = offset of the pointer (measured in bytes)

  • a3 = method in which the offset is to be interpreted (relative, absolute, etc.).

Name

Code

Description

SEEK_SET

0x1

Offset is to be measured in absolute terms

SEEK_CUR

0x2

Offset is to be measured relative to the current location of the pointer

SEEK_END

0x3

Offset is to be measured relative to the end of the file

Sleep

Causes the Jupiter Java thread to sleep for (at least) the specified number of milliseconds in register a1. This timing will not be precise, as the Java implementation will add some overhead.

Example

.globl __start

.text

__start:
  li a0, 19    # ecall code
  li a1, 1000  # sleep for 1 second
  ecall

Ecall Code

  • a0 = 19

Arguments

  • a1 = number of milliseconds

CWD

Stores the current working directory in a buffer whose address is in register a1.

Example

.globl __start

.data

  cwd: .zero 1024

.text

__start:
  li a0, 20  # ecall code
  la a1, cwd # buffer address
  ecall

Ecall Code

  • a0 = 20

Arguments

  • a1 = buffer address

Time

Stores the system time. a0 contains the low order 32 bits of system time and a1 high order 32 bits of system time.

Example

.globl __start

.text

__start:
  li a0, 21 # ecall code
  ecall

Ecall Code

  • a0 = 21

Arguments

  • none

Print Hex

Prints integer in register a1 in hex representation. Displayed value is 8 hexadecimal digits, left-padding with zeroes if necessary.

Example

.globl __start

.text

__start:
  li a0, 22  # ecall code
  li a1, 0xa # integer to print in hex
  ecall

Ecall Code

  • a0 = 22

Arguments

  • a1 = integer to print

Print Binary

Prints integer in register a1 in binary representation. Displayed value is 32 binary digits, left-padding with zeroes if necessary.

Example

.globl __start

.text

__start:
  li a0, 23  # ecall code
  li a1, 0xa # integer to print in binary
  ecall

Ecall Code

  • a0 = 23

Arguments

  • a1 = integer to print

Print Unsigned

Prints integer in register a1 as a 32-bit unsigned value.

Example

.globl __start

.text

__start:
  li a0, 23  # ecall code
  li a1, 0xa # integer to print (unsigned)
  ecall

Ecall Code

  • a0 = 23

Arguments

  • a1 = integer to print

Set Seed

Sets the seed of the corresponding underlying Java pseudo-random number generator.

Example

.globl __start

.text

__start:
  li a0, 25  # ecall code
  li a1, 123 # seed value
  ecall

Ecall Code

  • a0 = 25

Arguments

  • a1 = seed

Random Int

Stores the next pseudorandom, uniformly distributed, int value from the random number generator's sequence, in register a0.

Example

.globl __start

.text

__start:
  li a0, 26  # ecall code
  ecall

Ecall Code

  • a0 = 26

Arguments

  • none

Random Int Range

Stores the next pseudorandom, uniformly distributed, int value from the random number generator's sequence, in register a0. The next pseudorandom value will be in [a1, a2] range.

Example

.globl __start

.text

__start:
  li a0, 27  # ecall code
  li a1, 10  # lower bound
  li a2, 100 # upper bound
  ecall

Ecall Code

  • a0 = 27

Arguments

  • a1 = lower bound of range

  • a2 = upper bound of range

Random Float

Stores the next pseudorandom, uniformly distributed, float value in the range [0.0, 1.0] from the random number generator's sequence, in register a0.

Example

.globl __start

.text

__start:
  li a0, 28 # ecall code
  ecall

Ecall Code

  • a0 = 28

Arguments

  • none

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