[Coco] Assembler question

[Robert Gault]

Helio Emery Jr. wrote:
>
> Hi Robert, thanks for the response.
>
> I used to have a Brasilian Coco2 clone, named Color 64.
> While I don't manage to have one again in my hands, I'm using MESS as a Coco2 emulator to re-learn about Coco2 and OS-9 level 1 specifics.
> Back in the 80's the Color 64 was my second computer, and the one with I learned much from it.
>
> So, I started playing around using it to create some simple graphic programs in C and Assembler, just for fun.
> I created in C a program to draw a line and a circle in graphics mode, in OS-9 environment.
> And them I'm trying to create a program to do the same (draw a line and draw a circle) in Assembler.
> I'm not trying to recreate the C program itself in Assembler (i.e a didn't take a look in the assembled code generated by the C compiler).
> Just trying to get the line and the circle generated in graphics OS-9 environment.
>
> Reading OS-9 Operating System User’s Guide, Appendix C. Display System Functions I understood that for switchng to OS-9 graphics environment using the standart OS-9 calls one have to send to the STDOUT 3 caracters, the $0F (DISPLAY GRAPHICS) followed by graphics mode ($00 in my case) and graphics color (again $00).
>
> The problem is that only doing this is not enoght.
> In C I had to call fflush() to make the graphics screen to apear.
> In assembler I didn't know how to acomplish this.
>
> You see, even in OS-9 shell these caracters behave as described.
> If one uses the comand DISPLAY to send those characters to stdout, the system will change to graphics screen.
>
> In assemby I just call I$Write to send those characters to the screen.
> As you can see, I'm using this method to let OS-9 create the graphic screen for me, allocating the 6K screen area and using OS-9 GetStat to get the memory address.
> After doing this I'll just store the bytes I want directly in the graphics memory area.
> You do it in a different way?
> This is the only way I know right now.
>
> See bellow the assembler codes I'm using:
>
> plota1 leax inigrf,u    *
>            ldy #4            *
>            lda #STDOUT * Inicializa tela gráfica
>            OS9 I$Write   *
>            bcs erroos9    *
> plota2 lda #STDOUT
>            leax devsta,u *
>            ldb #DSTAT  * Obtem endereço da tela
>            OS9 I$GetStt *
>            bcs erroos9   *
>
>
> Thanks for the help,
> Helio
>
>

Well I tried a test with MESS and NitrOS-9 LevelI and Level2 using Coco2 and 
Coco3 emulation.
The program was

  ifp1
  use /dd/defs/defsfile
  endc

  mod endprgm,name,langtype,attrev,start,edata

edata equ .
name fcs "screen"
langtype set Prgrm+Objct
attrev set ReEnt+1

start lda #1       stdout
  leax cmd,pcr
  ldy #3
  os9 I$Write
loop bra loop

cmd fcb $f,0,0

  emod
endgrgm equ *
  end

The above on MESS Coco3 emulation running NitrOS-9 LevelII from a vdg screen 
turned on the graphics mode. Run on a window screen, nothing happened.

The above run on MESS Coco2 emulation with NitrOS-9 LevelI did not work but 
crashed NitrOS-9. The command   display f 0 0   did start the graphics screen.

I don't know why the above failed with Coco2 emulation but I don't think it is a 
problem with the program.