Testing it in the emulator, I saw that it only prints the output to the console (i.e. over RS232, not on the screen). So seeing nothing on the screen is expected.

Edit: syscall 341 prints to the screen

Writing a new compiler for C, in assembly, would be a huge project. I don't think it's realistically possible.
Porting some existing compiler would be easier, but may still be hard.

The Tiny C Compiler (tcc) has an ARM version, so possibly that can be ported.

Yes with 341, it works.
But with the syscall void gui_gc_drawLine(Gc p1, int p2, int p3, int p4, int p5), what is Gc p1? A pointer to the screen area?
And p2, p3, p4, p5? The coordinates of the line?

_{Edit (Eeems): Merged double post}

Gc is an OS variable. There is a bit of documentation on https://hackspire.org/index.php/Syscalls#Graphic_Context_API.

And if I want to reuse the return value of the syscall, in which register is the return value?

I'd guess in R0 as usual.

Hackspire says what the arguments do:

void gui_gc_drawLine(Gc, int x1, int y1, int x2, int y2) - Draws a line from <x1,y1> to <x2,y2>.

So you need to store Gc in r0, r1=x1, r2=y1, r3=x2, and then push y2 onto the stack. I'll write more later.

You don't construct a new one, you should get a pointer of the one used by the OS. It seems to be syscall 298, but I'm not sure if you can really just call it to get the pointer. It's a bit complicated to use the GC and you should read the documentation on hackspire if you really want to. It seems that its use has been deprecated in Ndless anyway.

Code: [Select]

main
    stmfd sp!, {r0-r12, lr}
    mov r0, #0xC0000010
    ldr r0, [r0]
    bl clrscrCX
    adr r0, text
    swi #46 ;tolower
    swi #341 ;disp_msg
    bl wait
    ldmfd sp!, {r0-r12, pc}

wait
    stmfd sp!, {r0-r12, lr}
    mvn r0, #0
    mov r0, r0, lsr #4
waitloop
    sub r0, r0, #1
    cmp r0, #0
    bgt waitloop
    ldmfd sp!, {r0-r12, pc}

clrscrCX
    stmfd sp!, {r0-r12, lr}
    mov r4, r0
    mov r5, #0
    mov r6, #0
    mov r7, #0
xloop
    mov r0, r4
    mov r1, r5
    mov r2, r6
    mov r11, r7
    bl setPixel
    add r5, r5, #1
    cmp r5, #320
    blt xloop
    add r6, r6, #1
    mov r5, #0
    cmp r6, #240
    blt xloop
    ldmfd sp!, {r0-r12, pc}

setPixel
    stmfd sp!, {r0}
    add r0, r0, r1, lsl #1
    add r0, r0, r2, lsl #9
    add r0, r0, r2, lsl #7
    strh r11, [r0]
    ldmfd sp!, {r0}
    bx lr

text
    dcb "HELLO WORLD!", 0
but he displays HELLO WORLD!

Yeah, tolower doesn't take a string argument. It only takes a single character and returns the lowercase version. Apparently it interprets the pointer as a non-uppercase character and returns it unchanged.

To make it work, you have to write  your own routine to change the whole string to lowercase.

You can always write a program in C on the computer, compile it with ndless, and then disassemble it to see how to do things. Compiling and disassembling the nGc sample would probably also be enough.

Is it possible to add smulbb, smulbt, smultb and smultt?
Signed 16 bit MULtiplication of Bottom half of first operand with Bottom half of second operand => SMULBB
And for smulbt or smultb or smultt :
T is Top and B is Bottom

---

And smlabb smlabt smlatb and smlatt also exist. It's same as mla, but with signed and bottom or top.

_{Edit (Eeems): Merged double post}