Main screen turn on
Working through the Baking Pi tutorials, I completed the first graphics tutorial.
I got my copy of CrossWorks for ARM activated last night, so I wrote it using that (but still using a Makefile to build it). I'm trying to build fluency in the editor, but there's a few nits I have with its editor. Namely, it likes to use spaces instead of tabs. In CrossWorks, by default my code would look like
.globl SetGpioFunction
SetGpioFunction:
cmp r0, #53
cmpls r1, #7
movhi pc, lr
push {lr}
mov r2, r0
bl GetGpioAddress
functionLoop$:
cmp r2, #9
subhi r2, #10
addhi r0, #4
bhi functionLoop$
add r2, r2,lsl #1
lsl r1, r2
str r1, [r0]
pop {pc}
However, I format with tabs between each column (so they all line up):
.globl SetGPIOFunction
SetGPIOFunction:
cmp r0, #53
cmpls r1, #7
movhi pc, lr
push {lr}
mov r2, r0
bl GPIOAddress
fnLoop$:
cmp r2, #9
subhi r2, #10
addhi r0, #4
bhi fnLoop$
add r2, r2,lsl #1
lsl r1, r2
str r1, [r0]
pop {pc}
In my editor, the tab stop is 8, so this looks a little more pronounced in my setup.
This is a slight variation on the MIPS assembly I used to write, which [ooks like[(http://p.kyleisom.net/tak.S.html):
tak:
ble $a0, $a1, takexit
addiu $sp, $sp, -32
sw $a0, 0($sp)
sw $a1, 4($sp)
sw $a2, 8($sp)
sd $ra, 16($sp)
addi $a0, $a0, -1
jal tak
sw $v0, 24($sp)
lw $a0, 4($sp)
lw $a1, 8($sp)
lw $a2, 0($sp)
addi $a0, $a0, -1
jal tak
sw $v0, 28($sp)
lw $a0, 8($sp)
addi $a0, $a0, -1
lw $a1, 0($sp)
lw $a2, 4($sp)
jal tak
lw $a0, 24($sp)
lw $a1, 28($sp)
move $a2, $v0
ld $ra, 16($sp)
addiu $sp, $sp, 32
j tak
takexit:
move $v0, $a2
j $ra
main:
dla $t0, args
lw $a0, 0($t0)
lw $a1, 4($t0)
lw $a2, 8($t0)
jal tak
dla $a0, result
dla $t0, args
lw $a1, 0($t0)
lw $a2, 4($t0)
lw $a3, 8($t0)
move $a4, $v0
jal printf
ori $v0, $0, 1
ori $a0, $0, 0
syscall
Slowly building out the pieces I'll need for the OS. I have this idea of building an OS that is like a Scheme-powered AppleBASIC ROM: the RPi should boot into a prompt where the user can enter Scheme programs. This week, I hope to write some serial interface code so I can send debug messages via the serial console.
Some of the code examples for screen01:
The source code lives in the bakingpi repo on Github; screen01 is here.