Division not working in the standard kernel

[freshbrood]

Am I doing something wrong? I understand that I need to insert "include div_mul.asm" at the start but it still doesn't seem to work with anything that doesn't divide evenly. n = 105 / 7 crashes.

n = (105 / 7) crashes. I don't need any floating number, I only want the int.

 

 

Also, unrelated, why are there only 6 banks listed in the dpc+ template instead of 8?
 

[+Andrew Davie]

17 minutes ago, freshbrood said:

Am I doing something wrong? I understand that I need to insert "include div_mul.asm" at the start but it still doesn't seem to work with anything that doesn't divide evenly. n = 105 / 7 crashes.

n = (105 / 7) crashes. I don't need any floating number, I only want the int.

 

 

Also, unrelated, why are there only 6 banks listed in the dpc+ template instead of 8?
 

 

Not a solution to your problem, but just a bit of advice: avoid division like the plague.

It is slow, and there are nearly always better ways to organise things into shifts and/or adds/subtracts/increments/decrements

For example, if you could somehow change the need for a 7 into an 8, then you could just shift right 3 times. 8 cycles.

The general purpose division routine is going to be lots more than that - say... 50... 100? More?

 

 

[+Andrew Davie]

Note to self: I'm assuming the division doesn't use the ARM!!!

 

[+splendidnut]

This probably should be posted in the BBasic sub-forum.

 

But I can give an answer for the last question:

You only have 6 code banks available in DPC+ (24k).  The other 8k is used as follows:   4k  is used for the Display Data RAM.  3k is used by the DPC bankswitching driver.  1k is used for music frequencies/only accessible via ARM code.

[+Karl G]

Yes, this should be in the bB forum. Your example should work, but make sure you put the "include div_mul.asm" before "set romsize" or "set kernel". If you have some code where this causes a crash, I'd be happy to take a look at it.

[jaybird3rd]

2 hours ago, Karl G said:

Yes, this should be in the bB forum.

I've moved the topic to batari Basic.

[+SpiceWare]

As @Andrew Davie mentions division by powers of 2 can be done fast, others not so much. That said, @Omegamatrix has a blog entry with a number of optimized division routines, such as this for divide by 7. Note that the code in the blog entry is messed up due to the last forum upgrade, so download the file DivisionRoutines(rev2).asm

;Divide by 7 (From December '84 Apple Assembly Line)
;15 bytes, 27 cycles
  sta  temp
  lsr
  lsr
  lsr
  adc  temp
  ror
  lsr
  lsr
  adc  temp
  ror
  lsr
  lsr

 

This is the DPC+ cartridge layout, can read more about it here - DPC+ARM - Part 6, DPC+ Cartridge Layout 

 

[ScumSoft]

Not sure if this addresses your 2nd question directly:

The template was made by me a long time ago, I don't know if it was updated after iesposta noticed an error in it.

Batari Basic indexes the banks starting at 1 through 6, the template said that bank 6 was reserved for the graphics bank because I had indexed the banks starting from 0 back then. Bank 6 is in fact usable as it translates to bank 5 as SpiceWare posted above.

 

So if your coding in ASM then DPC+ uses banks 0-5 for user code, bank 6 is reserved for the graphic data copies and fast fetcher access.

In bB you have banks 1-6 for use, and bank 7 is the graphics bank.

Edited January 6, 2021 by ScumSoft

[freshbrood]

Thanks for all your clear replies, I appreciate it! You save me a lot of headache and make writing games fun. I'm just getting into dpc now and even peeked at Karl G's asm for beginners tutorials, excellent. It's less daunting with you guys to help and your awesome input.
 

 

Btw I thought I was already posting in the batari forum??