Large String Wipes out all memory

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Summary:

I am just experimenting here but having an error like this without backups would be a nightmare.

Large String Wipes out all memory

Deoxal 01 Jun 2018 20:19

Note that I am using the TI-84+ SE

So I run the code below, and it terminates when Str1 reaches 8203 bytes, which is 2^13 bytes for the data plus 11 bytes for the data structure, which leaves me with 7786 bytes of unused RAM.

"V"→Str1
While 1
Str1+Str1→Str1
End

Then on the home screen I hit Vars, String, Str1, Enter. The calculator then shuts down and when I turn it back on, all of RAM is cleared. I tried the exact same thing 3 times with the same results.

However, if I create a new program that just uses Disp to show Str1, it works just fine. Also using Output(1,1,Str1) in another program will give a memory error, but does not affect the RAM or Archive.

Can any explain what is going on here?

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Last edited on 02 Nov 2018 06:53 by Deoxal Show more

Re: Large String Wipes out all memory

jonbush 01 Jun 2018 21:35

When you try to view the value of Str1 from the home screen with [Vars][String][Str1][Enter], the calculator attempts to load the value of Str1 into Ans. Since Str1 is larger than the remaining amount of RAM, this crashes the calculator. When you use Disp to display Str1, the calculator simply prints out the characters in the string without modifying the value of Ans.

Re: Large String Wipes out all memory

Deoxal 02 Jun 2018 05:34

I considered this, so on the homescreen I typed:

"1"+Ans

which gave me a memory error instead. Also I have maxed out 2 lists, and typed the name of one of the lists on the home screen and hit enter, which would store it to Ans, but this only gave me a memory error.

I was hoping for an explanation that explained what commands the calculator is actually performing, but if you know how I could analyze the calculator myself that would also be much appreciated. I was thinking of using the debugger in WabbitEmu, but I have never used it before.

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Last edited on 02 Nov 2018 06:55 by Deoxal Show more

Re: Large String Wipes out all memory

Trenly 02 Jun 2018 14:16

I don’t know much about z80, but from what I understand the strings are handled differently than any other sort of data value. The reason the string crashes and the list doesnt is because of their handling. When the string is stored to Ans, there is no error point in the OS which would cause it to stop. I believe this is because stings are handled as a single memory transaction. Lists however have this check because they only add one list item at a time to Ans and therefore when the memory buffer for Ans overflows it triggers the Err: memory. The string however, is so large that it overflows the memory buffer and starts storing to bits that its not supposed to be able to access. When it sores to those bits it is changing some other system variable, or possibly the OS itself. These overwritten bits are what cause it to crash. Best case is that it crashes when it doesnt have access to write to those bits and therefore gets suck in a sort of loop where it crashes, wort case is that it actually changes those bits

Re: Large String Wipes out all memory

Deoxal 03 Jun 2018 20:16

So I experimented with it a little bit more and found that the value seems to be already stored in Ans even though hitting enter does not evaluate it, rather hitting enter runs the program again, which instantly causes a memory error. First recall that I have 7786 bytes of RAM remaining. On the home screen I type "", to store the blank string to Ans, checking my memory, I now see that I have 15978 bytes of RAM left, but evaluating Str1 on the home screen, still crashes the calculator.

Also, I tried this on whole thing on my TI-84+ CE and I just got a memory error. So it seems TI just coded later calculators better, but there is no way this is a hardware issue, so TI just needs to update their OS.

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Last edited on 12 Jun 2018 22:33 by Deoxal Show more

Re: Large String Wipes out all memory

Trenly 03 Jun 2018 20:33

Thats because when you try to evaluate Str1 on the homescreen, even after ‘clearing’ Ans, it puts Str1 into Ans again

Re: Large String Wipes out all memory

Deoxal 03 Jun 2018 22:13

Ya, but if it had Str1 and Ans both taking up that much Ram, it should have crashed the first time.

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Re: Large String Wipes out all memory

Trenly 03 Jun 2018 23:30

Not necessarily, but that means the bug in the OS has to do with how the memory is handled when the display is called. Perhaps Xeda Elnara knows more about it.

Re: Large String Wipes out all memory

Deoxal 12 Jun 2018 22:50

Hi Trenly, I loaded TI-OS 2.43 onto my calculator, and I did the same exact thing and I did not even get an error. Instead it behaved how I would expect it to if I went to catalog and selected Ans, the same way Disp would, showing all V's and "…" . I would like to decompile the operating system to see what bug causes this. Do you know where I could find tools to do this? Thanks.

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Last edited on 18 Jun 2018 19:57 by Deoxal Show more

Re: Large String Wipes out all memory

Deoxal 17 Jun 2018 05:26

I'm updating this thread with what I have found if anyone is still looking at this.

I found that if I run the above program and then type Ans into a new program and run it, it will crash. However, if I type any commands after Ans it will not crash.

Once again if anyone knows anything about this bug, I'd really like to know.

Note: this only happens on 2.53MP and 2.55MP while using Mathprint.

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Last edited on 18 Jun 2018 19:48 by Deoxal Show more

Re: Large String Wipes out all memory

Xeda Elnara 27 Jun 2018 16:28

I did test the code on my calculator (2.55MP, MathPrint enabled) and it just threw an error. However, I am not surprised that it happened since the MP OSes are buggy, especially with displaying.

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Z80 Assembly>English>TI-BASIC>Python>French>C>0

Re: Large String Wipes out all memory

Deoxal 30 Jun 2018 05:29

I might of said this before, but I tried it in WabbitEmu and it happened there to, so that might be worth checking out.

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Re: Large String Wipes out all memory

(account deleted) 19 Jun 2018 14:35

How did you download 2.43? I tried installing the very first OS before, and I keep getting an error. I can't install any OS 2.53MP or lower onto my 84+.

(Anyways, I am not using the best mobile device to post this, My 3ds xl is kind of slow in the Internet Browser.)

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Hewwo, my name is Achak Claw. I was formerly BioHazard.

Re: Large String Wipes out all memory

Deoxal 30 Jun 2018 06:01

That means that you have boot code 1.03, which prevents you from downgrading beyond, 2.53MP. You can confirm this by typing [MODE][ALPHA][LN]. I have an older calculator with boot code 1.02. However, Texas Instruments did not guard the boot code well, so someone made a couple of programs to aid in getting around the new boot code. EpicFail and Flashy are programs by Brandon Wilson that can help you get around the security measures.

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Last edited on 03 Jul 2018 22:05 by Deoxal Show more