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Bit shift in Saturn minimalistic C program

Written by cafealpha 4 comments
While making a Saturn program running directly from ROM, constraint is usually to have program as small as possible. Why ? Because I would like to make Pseudo Saturn Kai continue supporting Action Replay, which have limited ROM size

So, in that situation, I use homemade, minimalistic stdlib, containing usually only memcpy and memset functions, and everything goes well.
But for some reason, current program was begging for __ashlsi3 and __ashrsi3 functions.
... What's these things ? __ashlsi3 is an assembly function doing left shifts of data, and as you probably guessed, __ashrsi3 does the same, but with right shifts

No problem, let's ask my friend google, and copy & paste theses functions without minding about their contents Theses functions are standard functions provided by C library, so sources can be found here and there.


An example of what __ashrsi3 function looks like

A day after that, here comes the time to do basic testing of this ROM code
Let's first start with simple things such as screen display ...


Text display ... not as expected ?!

Hrm, it's probably a problem in my printchar routine ?

printchar source code : this is the core thing
behind text display in my programs


But that's a very long time I didn't touched this routine, which works well on Pseudo Saturn Kai, and works even better in vdp1ex from Charles MacDonald sample programs, because all my printchar routines come from there
But just in case of, let's try to tune one " <<3 " into " *8 " in the code above, and see if that changes something. Theses two operations are equivalent, so this should give the same result, but ... Saturn screen becomes all black

Okay, there's definitely something weird regarding that printchar, but I just re-used it as-is from other project, so what's going wrong with my it ?!
[...]
And then (finally) a light-bulb above my head appears Maybe there's something wrong regarding the __ashlsi3 and __ashrsi3 routines ?
And, yes there was something wrong regarding theses routines ... I wrote a paragraph about them on the first half of this article, so it would be surprising the problem came from somewhere else

In more accurate words, routines are OK, which is normal since they are written by people smarter than me But the calling convention of __ashrsi3 was not as my gcc was expecting ?
Well, that's just a guess from the display results, because it seems to display the same pixel 8 times on each row of a given character, which may happen when ignoring shift parameter in __ashrsi3 function.

Anyway, rather than finding in details what's wrong, let's fix the problem First, with assembly by hand, in desperately trying to change input parameter handling ... I don't remember exactly what I wrote, but that was something like pushing a register to stack, moving parameter to it, finally restoring register, putting nop instructions everywhere, etc ... nothing difficult, but over my extent in assembly programming

The result is ... a mixed success :

Trying to modify __ashrsi3 routine by hand ... well, it seems that
some shift values are not correctly handled


Okay, so let's re-ask google about that __ashrsi3 routine ... and a different implementation arrives in search results. Let's try it


__ashrsi3

And the execution result :

Execution result with second version of __ashrsi3 function

Yeah, it works this time !!! And don't ask me why, because I didn't took time in understanding what's different in that second version of __ashrsi3 function
And, rather than understanding why it works ... let's close that assembly pandora box before some other mystic bugs pop from it

I will probably see about this in the future, but that was absolutely out of the scope of today's programming, and in software world, too much digression leads to freeze of projects, which I would like to avoid in order to go forward to next pending project 

As a example, I started to adapt yeti3d engine to Saturn in 2010 (7 years ago !), and this ended in ... developing a SD card based memory cartridge for Saturn !
The point above is is not a joke : menus used in my yeti3d adaptation are the origin of menus used in Pseudo Saturn Kai, which shows the continuity (co-consanguinity ? ) in my projects. And after getting yeti3d working a bit, I really would like to load levels from something else than CD-ROM, which was from PC (via adequate link cable) on a first time, and which will (should ?) then evolve to SD card.
That would be cool to make a Saturn game not requiring to burn CD-ROM somedays, but before that I need to finish neighboring side quests


Evolution of my Saturn projects

To conclude this article, let's say it was terribly fun to see some bits of the internals behind C language
By the past, I remember I did something similar with my yeti3d adaptation, but remained at "C language level" : optimization done at that time was (IIRC, ) to avoid 4 bits shifts, because theses are not available in a single SH-2 CPU instruction. Avoiding 4 bits shifts was simply done by merging two fixed point operation in a single one (or something like that : I did this 7 years ago !), and this actually gave some improvements in 3D scene rendering Theses were the good times ... I sometimes think "I'm Getting Too Old For This Shit", but that's only to motivate to finish my old projects

But before that, Pseudo Saturn Kai, and then Kicad and Quartus are waiting for me


BTW, in the case you wondered about what was today's programming session, you probably guessed it was about exception handler addition to Pseudo Saturn Kai. This not a new feature, since it was available in Pseudo Saturn 0.83x ... in fact, I grabbed some sources from Pseudo Saturn 0.83x in order to implement this exception handler (thank you CyberWarriorX !) This exception handler will be available as a small add-don to cheat codes feature in Pseudo Saturn Kai next major release.

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Gamer's Cartridge out of stock :]

Written by cafealpha 5 comments
Out of stock ":]". I'm glad to have finished this batch
I don't plan to sell Gamer's Cartridge for a while, because stock of parts to build theses cartridges (electronics components, PCBs, labels, etc) is currently very low here. I'm even lacking of bubble paper used when shipping cartridges

So, what's next ? Of course, Saturn stuff  I plan to use this "break" in cartridges manufacturing and sales in order to continue Pseudo Saturn Kai development.
Main feature to add is cheat codes, which is a bit "heavy" one to implement, because processing in order to make cheat codes working isn't documented in details.
But that will be done ! Also, there are some side quests here and there regarding Pseudo Saturn Kai features. I plan to implement as far I can, so it will be limited only by my free time, my motivation, and flash ROM remaining on cartridge

data/images/20170215_sgc_v33b_gerber_preview.tb.png
Gerber preview before ordering PCB on
Seeed Studio, very classy and realistic

Edit (2017/05/11) : finally back in stock
I catched the occasion to make some minor improvements to my homepage, such as adding anchor link to some sections, adding some directions for Japanese users, etc ... and I'm already full up with writing HTML

Edit (2017/05/12) : half of the stock already reserved oO
data/images/20170512_escalated_quickly.jpg
Cartridges are assembled by hand, hence stock is small, but I'm impressed anyway

Read more Gamer's Cartridge out of stock :]

The quick lazy brown dog jumps over the foxes ?

Written by cafealpha no comments
The quick lazy brown dog jumps over the foxes ?
The brown fox quick lazy jump jumps over the ?
The ... well, I forgot what it was, but just to say that I spent a some time in messing with fonts in my Save Data Manager application
In fact, it would be more accurate to speak about code pages (*), because I finally added support for Japanese text display :]

(*) For those who forgot what code pages was :
Once upon a time, before Unicode unified every characters, (and also made strlen function not working correctly on UTF-8 text), there was a custom for all countries in the developed world to define up to 128 extra characters that would be used in second half of ASCII character table.
Of course, Japan wanted to do the same, so it added poor looking "1 byte kana" characters on this extra 128 character page, and also added the remaining characters (including kanjis) after that, which gave birth to Shift-JIS encoding.

Since Saturn was developed, during this prehistoric "codepage" era, it is normal to find can find some code page remnants in Saturn software

One of these "code page remnants" is the comment string stored in each Saturn saves : didn't you noticed that sometimes BIOS displays Japanese characters in its save management screen ?

So, Save Data Manager must display Japanese characters instead of garbage characters when showing comment in save data selection menu !

data/images/20150704_save_delete_menu.png
What save comment looked like before
adding Japanese characters display ...
(It's a 6 months old screenshot)

How to do this ?
First, I need to verify that BIOS was defining characters according to Shift-JIS charset, and the best way to do this was to modify some save states and see what BIOS is displaying on screen.

And if possible, displaying as much as possible characters at once would improve the job's efficiency, so I choose to modify Keio Flying Squadron saves since they take only 32 bytes each.

So here comes the reason I choose a such weird title for this article : I wanted to display all font characters at once on screen
In the facts, I didn't used such a complex "lazy brown dog jump blah blah blah" sentence. I just displayed all the character in ascending order, and here is what it looked like in BIOS screen :

data/images/20160203_chars_katakana_raw.png
Repeat after me : -アイウエオカキクケコサシスセソ...
Looks good  That's definitely 1 byte kana characters in typical order.

Saturn BIOS also has ability to display European (accented) character, and switching from a codepage to another is just the matter of changing a byte per save data, so let's try and see what it looks likes :
data/images/20160203_chars_francais_raw.png
Same text as above, I just changed the language value

Oh, it looks like the good old ISO 8859-1 (latin1) charset

The picture above was displayed by setting French (my native language) language code in save, and setting to another language code (I tried with Spanish) gave unsurprisingly the same results.

So in the Saturn world, one byte equals one character, and there are two codepages to handle in order to display save comment string.
I first feared I had to deal with multi-byte characters (that is a real pain to handle when coding software), but that's not the case, and in fact it's relatively easy to do.

(2 hours later)
data/images/20160203_font_katakana.png data/images/20160203_font_francais.png
Katakana and European fonts

Hmm, theses characters are looking cute :)
It's seems that it is time to feed my image conversion tool ^^

(5 minutes later)
Okay, latin.bin and katakana.bin files are ready, I should add some codepage stuff in my text display code now !

(1 hour later)
data/images/20160203_font_test3_katakana_text_and_menu.png
Finally some exotic language displayed !
I lost 30 minutes in wondering why application wasn't
initially showing Japanese characters ... and it appears that
I was "cleaning up" the comment string by replacing exotic
character into space character
"It wasn't a bug, it was a feature "

It made sense when Japanese character wasn't displayed
correctly, but it was time to remove this string cleanup code.


Job complete ? Well, there are still some details to fix, and this is what take the most of time when developing software, but at least the boring part of the job is done :]



As a reward for me, I can now set save comment to a cool one when importing save data and that comment isn't defined.
I initially used a dummy "ImportData" string, but the holy "セガサターン,シロ" string defined in hitomi2500's ss-save-parser project is definitely better.
data/images/20160203_save_default_comment.png
セガサターン,シロ !


Last but not least : finishing this main quest opens doors to firmware translation side quest !
Well, Japanese translation would be ugly, because kanji characters are not available (just old-looking katakana characters : this article title would look like ザレージフォックスジャンプオーバーザブラウンドッグ on firmware :D), and on software side, handling multi byte characters is a real mess, so I don't want to do make a Japanese version of Pseudo Saturn Kai and Save Game Manager.

However, translation for European languages is now technically possible
Well, "possible" doesn't means I will do this right now  This is a low priority job, so I will do it when I will have enough time and motivation for it.

BTW, in order to test if exotic character display was OK on Pseudo Saturn, I tried to print "beta" glyph (defined in European codepage) on the title bar :
data/images/20160211_pskai_main_menu.png
Pseudo Saturn Kai main menu
Without any surprises (text display routines are common between Pseudo Saturn Kai and Save Data Manager), it works !
I can finally indicate that this is a beta version ^^





Edit : oops, the feature to inform me when a comment is posted seems (once again) not to work, and consequently I didn't noticed new comments :/

Here are the comments I replied so far. Since I'm late, they deserve to be re-posted here :

I am really happy to hear that you don't have cancer anymore!! Congratulations! I wish you a really long and happy life! :)     Anon

@Anon : It doesn't guarantee I'm cancer free !
CT scans indicate that there is no evidence of cancer relapse, but CT scan has limits (it doesn't shows millimeter-order tumors), so I continue regular cancer screening and taking care in everyday life

--------------
Hey @Spawn, could you upload those Saturn saves you have on your PC?
I have been looking for an archive of Saturn game saves for months now and I haven't found any.
Maybe with the save states I have, and your saves I can upload them somewhere and start an archive? I'll give you credit for it of course.     ReyVGM
@ReyVGM : Thank you for sharing your saves on segaxtreme !
They will be available for everybody on Save Data Manager, so that it will be easy to import on Saturn or emulator.

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best wishes for 2016 !!!     vbt
@vbt : Thank you ! Best wishes for 2016 too !!!
Well, we are already in February, sorry ^^;


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It's great to see your active development, cause my saturn projects are almost in hibernation today (i'm a bit in a time trouble). And i'm glad my code is of some use.
Good luck!     hitomi2500
@hitomi2500 : Hehe, I got some free time until end of March ... I don't know what it will be after that, but what's sure is that I will continue to have fun with my Saturn  Please keep continuing the good work too :]

--------------

stunned and confused

last night I went on a sega saturn nostalgia trip.

I had to catch up with 8+ years @ segaxtreme.
I found antime's usbcart, hitomi2500's fork, hitomi2500's new "wasca" and your stuff here.

sounds great ...
I need to dig up my saturn and finally start something.
I have a usb-cart from 2006 from pinchy (he seems inactive since 2007).     seal1
@seal1 : Hey, I remember seeing your nick in segaxtreme thread about yano/Freewing transfer device (I built a Freewing device at that time).
It was a long time before I made my first USB dev cart ... nostalgia.
Many members forgot about Saturn and left segaxtreme, but luckily vbt and antime are still active.
You're always welcome on segaxtreme, even if it just to say "hi"

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