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Posted: **Sun Oct 06, 2013 2:49 pm**

This is what to do at reset:

Set mapmode0 and reinstate the mapmode0 ROM
Set DP to #0
Set the I and F flags in CC to mask interrupts
Load PC from $FFFE

That's all. You shouldn't need a value for S as code executing after reset cannot assume it to be set.

Posted: **Sun Oct 06, 2013 7:49 pm**

Sarah wrote:You shouldn't need a value for S as code executing after reset cannot assume it to be set.

Note also that after reset, NMI stays disabled until a program sets S.

Posted: **Sun Oct 06, 2013 9:05 pm**

That's a little to hight for me, at the moment. e.g. what is "mapmode0" ?

Beside implementing more Opcode i have only implement some "Dummy" objects for PIA 1 & 2 and SAM...: https://github.com/jedie/DragonPy/blob/ ... #L336-L463

And without unittests for the new implemented Opcodes, i consider there are a few bugs

The current debug output is this: https://gist.github.com/jedie/6779646

I raised a NotImplementedError while writing to text screen:

Code: Select all

$ba7e read pc byte: $e7 from $ba7e
$ba7e	STB	INDEXED instruction_ST8	| $ba7e: $ba79-$ba85 - Clears text screen with value in B (CoCo $a92a)
$ba7f read pc byte: $80 from $ba7f
$ba80 addressing 'indexed' with postbyte: $80 == 10000000
$ba80 indexed addressing mode ea=$401 	| $401: $400-$5ff - Default Text screen
$ba80 get 'indexed' byte: ea = $401 m = $0
$401 instruction_ST8 kwargs: ea=$401 m=$0 opcode=$e7 operand=<B (8-Bit):96>
$ba80 ST8 store value $60 from B at $401 	| $401: $400-$5ff - Default Text screen
 **** TODO: write $60 '`' to text screen address $401

If i don't raise it will stay in this loop:

Code: Select all

$ba7e read pc byte: $e7 from $ba7e
$ba7e	STB	INDEXED instruction_ST8	| $ba7e: $ba79-$ba85 - Clears text screen with value in B (CoCo $a92a)
$ba7f read pc byte: $80 from $ba7f
$ba80 addressing 'indexed' with postbyte: $80 == 10000000
$ba80 indexed addressing mode ea=$401 	| $401: $400-$5ff - Default Text screen
$ba80 get 'indexed' byte: ea = $401 m = $60
$401 instruction_ST8 kwargs: ea=$401 m=$60 opcode=$e7 operand=<B (8-Bit):96>
$ba80 ST8 store value $60 from B at $401 	| $401: $400-$5ff - Default Text screen
 **** TODO: write $60 '`' to text screen address $401
 **** write $60 to $401 - mem info:
      $60: $5c-$61 - Floating Point Accumulator Num 2
      $401: $400-$5ff - Default Text screen
-------------------------------------------------------------------------------
$ba80 read pc byte: $8c from $ba80
$ba80	CMPX	IMMEDIATE instruction_CMP16	| $ba80: $ba79-$ba85 - Clears text screen with value in B (CoCo $a92a)
$ba81 read pc word: $05ff from $ba81
$ba81 addressing 'immediate word' value: $5ff
$ba81 instruction_CMP16 kwargs: ea=$ba81 m=$5ff opcode=$8c operand=<X (8-Bit):1024>
$ba83 CMP16 X $400 - $5ff = $-1ff
-------------------------------------------------------------------------------
$ba83 read pc byte: $23 from $ba83
$ba83	BLS	RELATIVE instruction_BLS	| $ba83: $ba79-$ba85 - Clears text screen with value in B (CoCo $a92a)
$ba84 read pc byte: $f9 from $ba84
$ba85 addressing 'relative' ea = $ba85 + -7 = $ba7e 	| $ba7e: $ba79-$ba85 - Clears text screen with value in B (CoCo $a92a)
$ba85 get 'relative' byte: ea = $ba7e m = $e7
$ba7e instruction_BLS kwargs: ea=$ba7e m=$e7 opcode=$23
$ba85 BLS branch to $ba7e, because C|Z==0 	| $ba7e: $ba79-$ba85 - Clears text screen with value in B (CoCo $a92a)
-------------------------------------------------------------------------------
$ba7e read pc byte: $e7 from $ba7e
$ba7e	STB	INDEXED instruction_ST8	| $ba7e: $ba79-$ba85 - Clears text screen with value in B (CoCo $a92a)
$ba7f read pc byte: $80 from $ba7f
$ba80 addressing 'indexed' with postbyte: $80 == 10000000
$ba80 indexed addressing mode ea=$401 	| $401: $400-$5ff - Default Text screen
$ba80 get 'indexed' byte: ea = $401 m = $60
$401 instruction_ST8 kwargs: ea=$401 m=$60 opcode=$e7 operand=<B (8-Bit):96>
$ba80 ST8 store value $60 from B at $401 	| $401: $400-$5ff - Default Text screen
 **** TODO: write $60 '`' to text screen address $401
 **** write $60 to $401 - mem info:
      $60: $5c-$61 - Floating Point Accumulator Num 2
      $401: $400-$5ff - Default Text screen

Posted: **Sun Oct 06, 2013 9:44 pm**

jedie wrote:That's a little to hight for me, at the moment. e.g. what is "mapmode0" ?

The map mode basically controls the configuration of RAM and ROM for a system using an MC6883 (SAM). You can read full details about how it decodes addresses in the data sheet:
http://images.ihscontent.net/vipimages/ ... -5-323.pdf

Or perhaps take a look at 'What can be done with it all' here:
http://archive.worldofdragon.org/index. ... 4K_Upgrade#

It's not really something you need to be concerned about whilst your emulator is in the early stages of development.

Posted: **Mon Oct 07, 2013 7:58 am**

Sarah wrote:Or perhaps take a look at 'What can be done with it all' here:
http://archive.worldofdragon.org/index. ... 4K_Upgrade#

Thanks! That's interesting!

Posted: **Mon Oct 07, 2013 8:23 am**

I ask myself if it's make more fun to start with a simpler hardware. e.g.: http://searle.hostei.com/grant/6809/Simple6809.html So i have only to implement a virtual RS232 interface

Posted: **Mon Oct 07, 2013 10:07 am**

The way I started with XRoar was to have some RAM, load the ROMs and periodically dump the state of 0x0400 - 0x05FF to the console using VT100 escape codes. Then I implemented CPU instructions basically in the order they're encountered in the BASIC ROM (obviously doing the "easy" stuff that was similar at the same time).

As things progress you need to flesh out a bit of the hardware at a time or fake it for the time being. Seeing the initial copyright message was really rewarding

Sadly I wasn't using version control beyond "copy the old files somewhere safe" at the time, so I can't trace through and see what got implemented when. Suspect once it sat there with a cursor flashing, some sort of proper video and keyboard input would have been next. It was good fun...

Posted: **Mon Oct 07, 2013 10:18 am**

sixxie wrote:The way I started with XRoar was to have some RAM, load the ROMs and periodically dump the state of 0x0400 - 0x05FF to the console using VT100 escape codes. Then I implemented CPU instructions basically in the order they're encountered in the BASIC ROM (obviously doing the "easy" stuff that was similar at the same time).

That's simmilar to my way. I get writes to 0x0400 (see post above):

jedie wrote:$ba80 ST8 store value $60 from B at $401 | $401: $400-$5ff - Default Text screen
**** TODO: write $60 '`' to text screen address $401

But i think '`' is a "wrong" char, isn't it?

sixxie wrote:Seeing the initial copyright message was really rewarding

Yes, is hope to get it at least to this point...

Currently i work on the support for Simple6809 and Dragon by changing the CLI arguments.

Posted: **Mon Oct 07, 2013 10:27 am**

jedie wrote: But i think '`' is a "wrong" char, isn't it?

It's just what 0x60 is in ASCII. On the VDG 0x60 is an empty character cell. The VDG character set is not a direct ASCII mapping - the BASIC ROM does the interpretation when you PRINT CHR$(...). For intelligible output you'll have to do a certain amount of translating values.

Posted: **Mon Oct 07, 2013 10:42 am**

sixxie wrote:
jedie wrote: But i think '`' is a "wrong" char, isn't it?
It's just what 0x60 is in ASCII. On the VDG 0x60 is an empty character cell. The VDG character set is not a direct ASCII mapping - the BASIC ROM does the interpretation when you PRINT CHR$(...). For intelligable output you'll have to do a certain amount of translating values.

Ah! that's good news! Thanks!

I have started to support for Simple6809 with: https://github.com/jedie/DragonPy/commi ... a03c5d7a9c

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