[ATARI 5200] How do I redefine characters in mode 1 (5 color text mode)

[Fabrizio Caruso]

Hi everyone,

 

I would like to redefine some characters in mode 1 (20x24 text 5-color mode).

 

I have managed to do this in C (with CC65) on the ATARI 800. How do I do this for the (very similar) Atari 5200?

I guess memory is not mapped the very same way.

Which locations/registers do I need to set to redefine the characters?
Which locations do I need to use to display the characters on the screen?

I know the foreground color is just an offset of the character (+0, +64, +128, +192)

Regards

 

Fabrizio

[sanny]

How do you do it on the 800? (Small code excerpt...)

[Wrathchild]

To the most part, I should think that the 5200 target for CC65 should be protecting you from most of this (https://cc65.github.io/doc/atari5200.html)

 

The major different however is that the shadow registers (assuming the O/S Vblank is still used and so copies the values to the chips) commonly in page 2 of the A8 line are in page zero for the 5200.

 

The main 'go-to' document for this is here

[Fabrizio Caruso]

For the Atari 8-bit line of computers, I do something like

void set_udg(void)
{
	extern char _FONT_START__[];
	unsigned char *CHBAS = (unsigned char *)0x2f4;

	memcpy(_FONT_START__, (void *)0xE000, 512);
	
	/* modify your font at _FONT_START__, etc, then set the new font: */		
	REDEFINE_AT(_FONT_START__);
	
	*CHBAS = ((int)_FONT_START__ >> ;  /* enable the new font */		
}

where REDEFINE_AT is a macro that writes at the right offsets of _FONT__START__ and so modifies just a few characters.


What do I need to change for the ATARI 5200?

[MaPa]

AFAIK Atari 5200 does not have shadow copy of CHBAS so you have to set the ANTIC $D409 register directly.

[Fabrizio Caruso]

@MaPa should all the rest work?
Are there fonts in rom at the same location?
Is there a character rom at all?

[sanny]

@MaPa should all the rest work?

 

More or less...

 

Are there fonts in rom at the same location?

 

No. They are at $F800.

 

Is there a character rom at all?

 

Yes.

 

 

regards,

chris

[Fabrizio Caruso]

Is the screen mapped in the same locations starting at 0xBD80?

[sanny]

Is the screen mapped in the same locations starting at 0xBD80?

 

You mean 0xBC80? No, it's at the address SAVMSC is pointing to.

 

regards,

chris

[Fabrizio Caruso]

I fear I won't be able to port my C code for the Atari 800 easily to the Atari 5200 because CC65 does not provide the same high level functions.

How do I set the 5 color in mode? I fear I will have to write straight into the corresponding registers...

[sanny]

Which high-level functions would you need?

[Fabrizio Caruso]

I need to choose the 5 colors of mode 1. I don't mind if it is just POKE at the right location/register or _set_color...

 

I also need to understand how to redefine characters.

For the Atari 800, I could do:

void set_udg(void)
{
	extern char _FONT_START__[];
	unsigned char *CHBAS = (unsigned char *)0x2f4;

	memcpy(_FONT_START__, (void *)0xE000, 512);
	
	/* modify your font at _FONT_START__, etc, then set the new font: */		
	REDEFINE_AT(_FONT_START__);
	
	*CHBAS = ((int)_FONT_START__ >> ;  /* enable the new font */		
}

where _FONT_START__ seems to be provided by the linker config and REFEFINE_AT is my macro that simply writes at the right offsets of _FONT_START__ so that some characters are modified.

I understand the *CHBAS has to be changed as well as 0xE000.

I was thinking of something like:

void set_udg(void)
{
	
	unsigned char *CHBASE = (unsigned char *)0xD409;

	memcpy(_FONT_START__, (void *)0xF800, 512);
	
	/* modify your font at _FONT_START__, etc, then set the new font: */		
	REDEFINE_AT(_FONT_START__);
	
	*CHBASE = ((int)_FONT_START__ >> ;  /* enable the new font */		
}

but what should I use instead of _FONT_START__, which location should I use for the new font definitions?

[Fabrizio Caruso]

I guess _FONT_START__ should point to any possible ram location that does not collide with my code.
I have no idea if and how it has to be aligned in memory and where the RAM is mapped on the Atari 5200.
By looking at the linker config, I guess it has to be within $0000-$3FFF.

Edited August 21, 2018 by Fabrizio Caruso

[Wrathchild]

fonts should align to a 1K boundary (i.e. a multiple of 0x400)

 

are you using the default linker config or rolling your own?

 

if you output a map file then you can see how much of the RAM space is being used.

Knowing that you should be able to get away with a fixed assignment, i.e.

#define FONT_AREA *(unsigned int *) 0x3800

[Fabrizio Caruso]

For the Atari 8-bit I only used $0200 bytes for the FONTS, so I assumed a 512-byte boundary. Am I wrong?

I have slightly modified the default linker cfg by adding:

MEMORY
...

FONT: file = "", start = $3E00, size = $0200, define = yes;
...

SEGMENTS

...
FONT: load = FONT, type = rw, optional = yes;


So in my code _FONT_START__ should point to $3E00

I in my code I have:

void set_udg(void)
{
	extern char _FONT_START__[];
	
	unsigned char *CHBASE = (unsigned char *)0xD409;

	memcpy(_FONT_START__, (void *)0xF800, 512);
	
	/* modify your font at _FONT_START__, etc, then set the new font: */		
	REDEFINE_AT(_FONT_START__);
	
	*CHBASE = ((int)_FONT_START__ >> ;  /* enable the new font */		
}

Where REDEFINE_AT is writing at the right offsets startinf from _FONT_START__ in order to modify some characters.

[MaPa]

For the Atari 8-bit I only used $0200 bytes for the FONTS, so I assumed a 512-byte boundary. Am I wrong?

 

 

Yes, you are wrong The charset needs to be at 1k boundary.

[Fabrizio Caruso]

THANKS!

I understand that the memory address is not fixed and it is the adress pointed to by SAVMSC ($1B).
What causes SAVMSC to change?
For the Atari 8-bit computer series I used the fixed address $BD80 instead of variable one.
A fix address is better for me because I can keep the same code for all my (many) targets.

[Fabrizio Caruso]

I have used the fixed screen memory address $3E20 (pointed by SAVMSC by default?) and it works!!

Which registers do I need to write to, in order to set the four foreground colors? (I want to keep black as background).

[Wrathchild]

From the porting guide: $08-$10 Shadows for COLPMO through COLBK

[Fabrizio Caruso]

I have managed to find the registers! I am writing on $0C-$10 and it works!
My game now has nice graphics on the Atari 5200!

[Fabrizio Caruso]

I now need to port the sound routines.
For example for the Atari 8-bit computer series I do:

	void _explosion_sound(unsigned char freq)
	{
		unsigned short i; 
		POKEY_WRITE.audctl = 0x00; 
		POKE(53775u,3); 
		POKEY_WRITE.audf1 = freq; 
		POKEY_WRITE.audc1 = 0x07; 
		for(i=150;i>0;--i) 
		{ 
			POKEY_WRITE.audc1 = i/10u; 
		} 
	}

CC65 provides POKEY_WRITE apis. I assume they are correctly implemented.
I need to figure out how to port
POKE(53775u,3);
to the Atari 5200

[Wrathchild]

POKEY_WRITE.skctl = 2

[Fabrizio Caruso]

Thanks! It works on the Atari 8-bit AND on the Atari 5200!

Edited August 22, 2018 by Fabrizio Caruso

[Fabrizio Caruso]

How can I prevent to trigger the sleep mode on the Atari 5200?

Would POKE(77,0) work as on the Atari 8-bit computers?

[Wrathchild]

Please take a look through the porting guide... "$04 - Attract mode timer/flag"

 

With SKCTL, the "Bit 0 of SKCTL, the debounce enable bit, need not be set in the 5200"

(when comparing a same title's A8 & 5200 code, the A8 uses 3 and 5200 uses 2)