A little PASM help, please!

markaeric

Alas, my first foray into PASM. My only previous encounter with ASM was a little bit on the SX, and that's pretty much all forgotten (except for having to move vars to the working register).

Anyways, I know this is real simple, so don't laugh at me too hard!

What I'm trying to do is write data to an array in cog ram. How do I go about addressing each long? Do I simply add some sort of label at the beginning of the array, and then do something like:

add LabelName, 1
mov LabelName, Data

or do I have to create another variable which I use to point to the array? If so, how do I go about doing that? I've been searching for the answer, but didn't come across it. If I did, then I certainly didn't recognize it. I did see an example in Phil Pilgrim's tricks and traps, but there seemed to be some additional complexities that I was confused about.

Thanks,
Mark

Harley

In your VARs, you need to set up an array

VAR array(value of length of array)

Now Spin can access this array if needed. When you do 'cognew' use the array label as 2nd expression. Then in PASM, PAR provides you access to this array. You need RDLONG or WRLONG to read from/write to the array. Increment pointer to PAR by 4 for each location. Note, WRLONG uses 'value' in the destination and pointer in the source; a bit bass-ackward.

At least this is the way I understand and have used arrays. I've used a 300+ array for an A/D, with the first two locations reserved to pass variables between Spin and PASM.

Don't fall into the trap of accidently assigning less locations to the array than PASM uses. That cog trampled over the variables following 'array' making for a mess to debug

Cluso99

You are referring to an array in Cog Ram.

mov ArrayPtr, #Array 'setup the pointer to the first array data address
.....
loop xxx xxxx, ArrayPtr 'do something with the array long
add ArrayPtr, #1 'point to next array long
jmp #loop



ArrayPtr long 0
Array long 0
long 0
long 0

markaeric

Cluso99 wrote: »

You are referring to an array in Cog Ram.

mov ArrayPtr, #Array 'setup the pointer to the first array data address
.....
loop xxx xxxx, ArrayPtr 'do something with the array long
add ArrayPtr, #1 'point to next array long
jmp #loop



ArrayPtr long 0
Array long 0
long 0
long 0

Makes perfect sense! Thanks!

kuroneko

markaeric wrote: »

Makes perfect sense! Thanks!

It does? Cog array access without indirection?

markaeric

Nope.. Nevermind.. I don't get it.

I'm messing a bit with movd now. Not sure if it even works yet. Is there a different way?

Edit: Doh! Now I found this thread: http://forums.parallax.com/showthread.php?t=118875

Cluso99

With movd, movs and movi don't forget that it takes an instruction in between due to pipelining in the prop.

ericball

To access an array in HUB RAM:

' data = BASE[INDEX]
	MOV	ptr, INDEX
	SHL	ptr, #2		' 1 for WORD, 2 for LONG, not required for byte
	ADD	ptr, BASE
	RDLONG	data, ptr

' data = BASE[i++]
	MOV	ptr, BASE
	RDLONG	data, ptr
	ADD	ptr, #4		' 1 for BYTE, 2 for WORD, 4 for LONG

If the array is in COG RAM then you use self modifying code:

' data = BASE[INDEX]
	MOVS	S1, #BASE
	ADD	S1, #INDEX
	NOP			' required for pipeline
S1	MOV	data, BASE+0

' data = BASE[i++]
	MOVS	S1, #BASE
S1	MOV	data, BASE+0
	ADD	S1, #1		' may be placed before MOV data if desired

markaeric

I do see now. I was a bit mislead due to compile-time addressing.