Newbie Questions

Parallel Universe

I have a couple of newbie questions about addresses. I know they're 16 bit words for each·main memory byte, but I don't understand a couple of things.

1. If the par register cuts off the lower two bits of an address, how do you pass the address of a word with cognew to an assembly program?
2. In TV.spin, how do you get the tile address into 10 bits? What bits do you cut off?

Thanks

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Mike Green

1) Strictly speaking you can't. It's always a word address. If you don't plan on passing ROM addresses (in the upper 32K), you can shift the word address left by one bit when passing it and shift it right by one bit in your assembly routine to get a word address.

2) The tile address is the upper 10 bits of a 16 bit address. It's always on a 64 byte boundary. Since all tiles are 16 longs or 64 bytes, this makes sense. In the ROM, the tiles for the characters are on 64 byte boundaries. If you're supplying the tiles, they do have to be allocated on a 64 byte boundary. Since Spin has no provision for doing this for you, you have to do it yourself by allocating an area dynamically on a 64 byte boundary.

Phil Pilgrim (PhiPi)

1. Either shift the word's address left by one bit (and write the ASM code to shift it back to the right), or make sure the word is on a long boundary.

-Phil

potatohead

...or pass the address of a long aligned block of parameters to be passed, where one of those is your word address.

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Parallel Universe

Thanks fror responding so quickly!
I should have clarified that I'm trying to pass a variable. After a little experimentation I discovered that the compiler aligns the first variable of an object to a long boundry. Mystery 1 solved!
But how do you make sure that your tile is· on a 64 byte boundry? Do you define it in a DAT block and then move it to a set address so that you know it's on a 64 byte/16 long boundry?

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stevenmess2004

I allocated 63 more longs than necessary and then just 0d the last x bits. It wastes memory but it works. The other option is to put it in the memory after the stack.

potatohead

Here's a good thread on that: http://forums.parallax.com/forums/default.aspx?f=25&m=210053

Coupla options presented, including overallocate.

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Parallel Universe

So how about something like this:

CON
  tile_count
 
PUB tile_init : new_address
  ...
  new_address := @tile_buf>>6<<6
  longmove(new_address, @tile1, tile_count)
 
DAT
tile_buf '15 longs
...
 
tile_1 '16 longs
...

I assume that longmove can overwright the data·as·it's copying for this to work, otherwise I'd just have to put it beyond the stack.

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Paul Baker

Yes longmove appropriately observes overlaping regions.

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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

deSilva

@PU: Not quite... it should be @tile_1>>6<<6

Parallel Universe

That's what I ment to do, I guess I was thinking that tile_buf was the address of the END of the buffer for some reason.

Sorry about the black box in my last post, the forum messed up.

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Parallel Universe

Thanks to your advice, my TV is displaying my initials in COLOR! · Thanks!

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