Re: Writing a TSR that stores/restores the video screen (C with inline Asm)
Posted on 2024-05-08, 10:47
Thank you for all your help with this 😀
Re: Writing a TSR that stores/restores the video screen (C with inline Asm)
Posted on 2024-05-08, 08:10
So I have rewritten most of the code, its much less of a mess now and it almost works :) I can now process the keys within the TSR and exit it too, but when back to the state before calling the TSR, keyboard no longer works. Its not frozen though as I can all the TSR again and it still works, the …
Re: Writing a TSR that stores/restores the video screen (C with inline Asm)
Posted on 2024-05-08, 06:39
I see, you are right, I did somehow considered mainTSR to be the main program and expected that when the execution was in there and a key was pressed, the handler would get called anew. Which is why I have the complicated switching within the handler itself. But as you describe it, its probably not …
Re: Writing a TSR that stores/restores the video screen (C with inline Asm)
Posted on 2024-05-07, 14:25
After reading this, I am clearly in way over my head. But I am not giving up just yet. I take it by acknowledging the PIC you mean outputting 0x20 to port 020, right? I rewrote the program to use the typical simple game key handling. It not longer freezes unless I try to wait for ESC to be pressed. …
Re: Writing a TSR that stores/restores the video screen (C with inline Asm)
Posted on 2024-05-07, 11:24
I have narrowed it down to one line, surprisingly its nothing to do with the store/restore or interrupts per se, its this line: while (inportb(0x60) != 1) oldKeyHandler(); When I comment it out, it works. Apparently DOS, unlike DOSBox, doesnt like the keyboard port to be hammered, even by a read. So …
Re: Writing a TSR that stores/restores the video screen (C with inline Asm)
Posted on 2024-05-07, 11:12
It's not a precaution if it's not needed and damaging things when used :) Share the updates. It was during the phase when I added tons of pushes and pops everywhere :) I just removed the CLI/STI and replaced (...) with (), no more updates yet. Going to start testing it by commenting parts out. Ok, …
Re: Writing a TSR that stores/restores the video screen (C with inline Asm)
Posted on 2024-05-07, 10:04
Alright, I removed the CLI/STI, it was just a precaution anyway. The (...) is there because I was compiling is as CPP and it otherwise complained, wanting the ... to be there. Changed it to C and now, as it is plain C, and it takes just () giving warnings about an unknown funcion prototype, but no …
Re: Writing a TSR that stores/restores the video screen (C with inline Asm)
Posted on 2024-05-07, 08:48
Post the code :) I know I am being a bother, but why is my happiness alway SO short lived? :) The code works great in DOSBox so why does it wreak havoc on the real thing? It does load and show the text message there with the buzzing sound and a hard lockup. So it could be just anything, even the …
Re: Writing a TSR that stores/restores the video screen (C with inline Asm)
Posted on 2024-05-07, 08:32
So I changed it to static and it works fine in DOSBox, but it freezes instantly in real DOS 6.22 on my 486 with a weird buzzing sound, probably from the speaker 🙁 I know DOSBox is meant to work great for games and possibly not other software, but its still quite a disappointment.
Re: Writing a TSR that stores/restores the video screen (C with inline Asm)
Posted on 2024-05-07, 08:20
"Seems to work" is a bad argument with dos :) It works until conditions change radically enough to break your assumptions. True, I will change it back to static. 4KB of static buffer vs 200 bytes of code to allocate and use XMS - that's a worth trade. Good point. I will try that if the buffers …
Re: Writing a TSR that stores/restores the video screen (C with inline Asm)
Posted on 2024-05-07, 07:59
I mean I hear you, but I have a NULL test in there to return when the memory is not allocated and it is still working, even when called from BC++. Maybe the malloc function is just misfiring and not reporting the problem because its not meant to be used in a TSR?
Re: Writing a TSR that stores/restores the video screen (C with inline Asm)
Posted on 2024-05-07, 07:54
You must allocate entire needed buffer in the data segment, which will survive the exit, and take few additional KBs of conventional memory, but it will be exclusively yours. Thats strange, it seems to work now in both EDIT and BC++, with dynamic allocation. But I will change it back to static to …
Re: Writing a TSR that stores/restores the video screen (C with inline Asm)
Posted on 2024-05-07, 07:43
Try declaring your saving area as a static array first, avoid using heap which will not exist after your app exists when installing TSR. Yay, you nailed it!! When I changed screen_state to a static array, of course the asm complained with the LES/LDS commands. So I created a pointer to this static …
Re: Writing a TSR that stores/restores the video screen (C with inline Asm)
Posted on 2024-05-07, 07:37
There is a point to clarify... You've used malloc() to allocate memory. That memory comes from the heap when the app is loaded, and the heap is the entire low memory above your exe image. But then you exit to make your app TSR, the heap is discarded. The save_state now points past the app …
Re: Writing a TSR that stores/restores the video screen (C with inline Asm)
Posted on 2024-05-07, 07:16
See the lines 40/41. It loads the DGROUP segment into BP then moves it into DS. It's exactly the same what gets loaded into AX in the line 84. You didn't need to load DS explicitly later. So it means BC++ generates safer code than expected, at least that. It was actually a bit to be expected …
Re: Writing a TSR that stores/restores the video screen (C with inline Asm)
Posted on 2024-05-07, 07:01
jmarsh wrote on 2024-05-07, 06:43: Assume it loads all the bytes in one instant then sets the new values in DS and SI. Good to know, thanks.
Re: Writing a TSR that stores/restores the video screen (C with inline Asm)
Posted on 2024-05-07, 07:00
So, yeah. You don't really need to take care of DS or other registers, Borland C++ 3.1 does that for you. I can confirm that now too, I checked the generated asm. It pushes everything. Dont want to bloat it here too much, so please check this: https://paste.ofcode.org/4enD6JkKZMxbYRt96ht7Zq Maybe …
Re: Writing a TSR that stores/restores the video screen (C with inline Asm)
Posted on 2024-05-07, 06:39
Oh and about preserving the registers in my newKeyHandler - the "interrupt" keyword I use in the handler definition is supposed to "save all CPU registers and terminate the funcion with IRET" so I guess I dont need to explicitly PUSH/POP anything there.
Re: Writing a TSR that stores/restores the video screen (C with inline Asm)
Posted on 2024-05-07, 06:36
The "seg something" works with a known symbol (variable/function). You write "seg something", compiler puts the reference to that something in the object file, and the linker then will create appropriate relocation record in the exe, so during execution that "seg something" turns into the real …
Re: Writing a TSR that stores/restores the video screen (C with inline Asm)
Posted on 2024-05-07, 06:24
loads a 32bit/far pointer, of segment:offset from the pointer variable screen_state into ES:DI loads the SEGMENT (that the variable) screen_state (is part of), and then takes the OFFSET (the address) of the variable. After reading those two lines a dozen times, I think I finally get the difference, …
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