Print a formatted line

This is a short output-formatting recap. In the Playground, put a service number in a7, put its input in the register that service expects, and run ecall. Here the program builds one console line from text, a number, and one character:

.data
label: .asciz "Items: "

.text
.globl main
main:
    li a7, 4            # service 4: print a zero-terminated string
    la a0, label
    ecall

    li a7, 1            # service 1: print a signed integer
    li a0, 42
    ecall

    li a7, 11           # service 11: print one character
    li a0, '\n'
    ecall

    li a7, 10           # end this Playground run
    ecall

The console reads:

Items: 42

The register names are familiar from function calls. For this Playground request, a7 temporarily holds the service number and a0 holds the first input. Watch a0 as the program runs: it first holds the address of label, then the number 42, then the newline character. Each ecall uses the values currently in those registers.

Because service 4 needs a zero-terminated string, this declaration uses .asciz. Its seven characters take seven bytes, and .asciz adds an eighth byte whose value is zero. Service 4 starts at the address in a0 and prints through that zero. .ascii does not add it, so service 4 could continue into later data instead of stopping after the label.

The three services each print one kind of value: service 4 prints a zero-terminated string, service 1 prints a signed 32-bit integer, and service 11 prints one character. That is why the line needs three requests. The final exit request ends this Playground run deliberately.

Format a greeting

Make the console read exactly Hello Ada followed by a newline. Print the two supplied strings with service 4. Print the space and newline one character at a time with service 11, then end the run with service 10.

.data
greeting: .asciz "Hello"
name:     .asciz "Ada"

.text
.globl main
main:
    # print greeting, a space, name, and a newline
    # then end the Playground run

.data
greeting: .asciz "Hello"
name:     .asciz "Ada"

.text
.globl main
main:
    li a7, 4
    la a0, greeting
    ecall

    li a7, 11
    li a0, ' '
    ecall

    li a7, 4
    la a0, name
    ecall

    li a7, 11
    li a0, '\n'
    ecall

    li a7, 10
    ecall