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Added more comments and moved delay value to rodata

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Perry Kivolowitz 2022-11-01 10:58:10 -05:00
parent b2563648a0
commit 26f59281cb
1 changed files with 18 additions and 7 deletions
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25
projects/walkies/main.s
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@ -17,22 +17,28 @@
back (-1 to 1) back (-1 to 1)
*/ */
.equ MAX_COLUMN, 60 .equ MAX_COLUMN, 60 // These are equivalent to
.equ NUM_CHARS, 4 .equ NUM_CHARS, 4 // #define in C and C++
counter .req w20 counter .req w20 // These also but these are for
delta .req w21 delta .req w21 // use with registers
.section .rodata .section .rodata // In essence: const
CHARS: .asciz "|/_\\" CHARS: .asciz "|/_\\"
TRM: .asciz " \r" // The space is important. TRM: .asciz " \r" // The space is important.
usec: .int 75000 // 0.075 seconds delay AT LEAST
.text .text
main: stp x29, x30, [sp, -16]! main: stp x29, x30, [sp, -16]!
stp counter, delta, [sp, -16]! stp counter, delta, [sp, -16]!
// counter will move up and down between MAX_COLUMN and 0
// by toggling delta from 1 to -1 and back. This is far
// simpler than creating dual for loops which one might do
// in a naive implementation.
mov counter, wzr mov counter, wzr
mov delta, 1 mov delta, 1
mov w0, wzr mov w0, wzr
@ -40,6 +46,8 @@ main: stp x29, x30, [sp, -16]!
0: bl Pad 0: bl Pad
bl Emit bl Emit
bl Terminator bl Terminator
// Having completed output for this animation cycle, adjust
// counter toggling delta if necessary.
add counter, counter, delta add counter, counter, delta
mov w0, MAX_COLUMN mov w0, MAX_COLUMN
cmp w0, counter cmp w0, counter
@ -49,6 +57,7 @@ main: stp x29, x30, [sp, -16]!
1: cbnz counter, 2f 1: cbnz counter, 2f
neg delta, delta neg delta, delta
// Cause the delay between animation cycles.
2: ldr x0, =usec 2: ldr x0, =usec
ldr w0, [x0] ldr w0, [x0]
bl usleep bl usleep
@ -62,7 +71,8 @@ main: stp x29, x30, [sp, -16]!
ret ret
/* Terminator - outputs "\r " - notice the space after /* Terminator - outputs "\r " - notice the space after
the carriage return. the carriage return. It is important. Try redoing this
with the space removed to see why.
*/ */
Terminator: Terminator:
@ -134,5 +144,6 @@ mod: sdiv x2, x0, x1 // x2 gets a // b
.data .data
buff: .space 4 buff: .space 4
usec: .int 75000
.end