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Author Topic: How do apps work?  (Read 12106 times)

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Offline squidgetx

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How do apps work?
« on: December 11, 2010, 08:18:38 pm »
Not exactly an asm question, but I figured I'd have the best audience in this board.

So my question is, how do apps run without using up user RAM? Are they copied to a page reserved for apps? And if so, at what location/address is that?

« Last Edit: December 11, 2010, 08:19:02 pm by squidgetx »
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Offline FloppusMaximus

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Re: How do apps work?
« Reply #1 on: December 11, 2010, 10:19:58 pm »
Seems like a fine asm question to me.

Apps are stored in Flash, and execute from Flash, just like the OS.  Flash is divided into 16384-byte "pages"; any page can be mapped to the Z80 address space starting at 4000h, simply by writing the page number to port 6.  So basically, all the OS needs to do to run an app is to write the appropriate value to port 6, and jump to the start of the app's code.  The app is never copied into RAM - there's no free RAM you could use for that purpose.

In order for this to work, the app needs to be stored at the start of a page, which is why every app effectively takes up a multiple of 16k bytes.  Being stored in Flash also means the app can't modify itself (well, that and the fact that they need to be digitally signed.)
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Offline jnesselr

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Re: How do apps work?
« Reply #2 on: December 11, 2010, 10:21:28 pm »
Quote from: FloppusMaximus on December 11, 2010, 10:19:58 pm
Seems like a fine asm question to me.

Apps are stored in Flash, and execute from Flash, just like the OS.  Flash is divided into 16384-byte "pages"; any page can be mapped to the Z80 address space starting at 4000h, simply by writing the page number to port 6.  So basically, all the OS needs to do to run an app is to write the appropriate value to port 6, and jump to the start of the app's code.  The app is never copied into RAM - there's no free RAM you could use for that purpose.

In order for this to work, the app needs to be stored at the start of a page, which is why every app effectively takes up a multiple of 16k bytes.  Being stored in Flash also means the app can't modify itself (well, that and the fact that they need to be digitally signed.)
Wait, are they checked every time they are run for digital signatures?
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Offline FloppusMaximus

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Re: How do apps work?
« Reply #3 on: December 11, 2010, 10:30:39 pm »
No, only when it's transferred to another calculator (it's checked at the receiving end, that is.)
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Offline ZippyDee

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Re: How do apps work?
« Reply #4 on: March 24, 2011, 01:24:23 am »
Why does it have to be signed? (I've never understood the whole signing thing with apps)
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Offline mikehill2003

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Re: How do apps work?
« Reply #5 on: March 24, 2011, 01:32:13 am »
Quote from: ZippyDee on March 24, 2011, 01:24:23 am
Why does it have to be signed? (I've never understood the whole signing thing with apps)

If they are signed (I have no idea if they are) it would be to control who could make programs.
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Offline z80man

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Re: How do apps work?
« Reply #6 on: March 24, 2011, 01:39:34 am »
But if you used your own link protocol, could you send an app to another calculator without having to sign it correctly.
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Offline DJ Omnimaga

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Re: How do apps work?
« Reply #7 on: March 24, 2011, 01:42:27 am »
Welcome to the forums ZippyDee!

I do not know why they are signed, but I suspect this is some protection TI added to their calcs to make it harder to distribute paid ones. However I have no clue why freeware apps still need to be signed.
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Offline mikehill2003

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Re: How do apps work?
« Reply #8 on: March 24, 2011, 01:49:13 am »
Quote from: z80man on March 24, 2011, 01:39:34 am
But if you used your own link protocol, could you send an app to another calculator without having to sign it correctly.

Can you?
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Offline DJ Omnimaga

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Re: How do apps work?
« Reply #9 on: March 24, 2011, 01:53:03 am »
Wait I missed that post. That would be awesome if this was possible. O.O

The only problem is that such apps gets auto-deleted after being ran 16 times, though... (since the calc thinks they are trial apps). Take Axe Parser-generated apps, for example.
« Last Edit: March 24, 2011, 01:53:26 am by DJ_O »
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Offline mikehill2003

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Re: How do apps work?
« Reply #10 on: March 24, 2011, 01:54:43 am »
Quote from: DJ_O on March 24, 2011, 01:53:03 am
Wait I missed that post. That would be awesome if this was possible. O.O

The only problem is that such apps gets auto-deleted after being ran 16 times, though... (since the calc thinks they are trial apps). Take Axe Parser-generated apps, for example.

Whoah! LAME

They couldn't make a better trial system then that?
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Offline DJ Omnimaga

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Re: How do apps work?
« Reply #11 on: March 24, 2011, 02:16:57 am »
Well... it's Texas Instruments we're talking about here, after all. :P

(Although if Casio tried to lock down the Prizm, then they failed even harder, since it got cracked a few weeks after its release)
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Offline z80man

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Re: How do apps work?
« Reply #12 on: March 24, 2011, 02:56:47 am »
Quote from: DJ_O on March 24, 2011, 02:16:57 am
Well... it's Texas Instruments we're talking about here, after all. :P

(Although if Casio tried to lock down the Prizm, then they failed even harder, since it got cracked a few weeks after its release)
A couple of weeks, I'm pretty sure we got our own apps on in under a week. In fact we were running apps before the announced release of the Prizm on January 15th.

I never knew that Axe apps were deleted after 16 runs ??? Probably because I've never ran one of my Axe apps more than 16 times before recompiling. but still it just sounds strange to see apps get deleted like that.
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Offline Freyaday

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Re: How do apps work?
« Reply #13 on: March 24, 2011, 03:04:38 am »
Yeesh. So is it possible to sign an app on calc, or does it have to be done on a computer?
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Offline ZippyDee

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Re: How do apps work?
« Reply #14 on: March 24, 2011, 04:04:16 am »
Quote from: DJ_O on March 24, 2011, 01:42:27 am
Welcome to the forums ZippyDee!
Thanks :D

Quote from: DJ_O on March 24, 2011, 01:53:03 am
The only problem is that such apps gets auto-deleted after being ran 16 times, though... (since the calc thinks they are trial apps). Take Axe Parser-generated apps, for example.
Well then that answers the question of why they need to be signed, so I guess the only question left is
Quote from: Freyaday on March 24, 2011, 03:04:38 am
Yeesh. So is it possible to sign an app on calc, or does it have to be done on a computer?
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