Linked list in pasm

Ray0665

I am having difficulty with a linked list in PASM


The pasm routine is started from spin as follows
P1 := @L1
cognew(@begin,@P1)


In the PASM I fetch the starting address like this
DAT
ORG 0
Begin mov Ptr,par
rdlong NextPtr,Ptr ' Save the link
add Ptr,#4 ' Point to the data
<<< do stuff with data >>>>


and now I want to advance to the next element so I do this
mov Ptr,NextPtr


But it does not work where am I going wrong?


the list is defined like this, at the end of the DAT block


L1 long @L2, <data>
L2 long @L3, <data>
L3 Long @L1, <data>

Dave Hein

Addresses stored in a DAT section using the @ operator are actually object offsets, and not absolute addresses. The top object starts at address 16. You need to add 16 to the object offsets as follows:

L1 long @L2+16, <data>
L2 long @L3+16, <data>
L3 long @L1+16, <data>

If this is not in the top object you will need to add the object starting address to each address value at runtime.

Ray0665

Got it, Now is there a way to capture the starting offset symbolically
for example could I define the links like this
L1 long @L2+begin,<data> where begin is the first label

Dave Hein

I don't know of any way to get the starting address within a DAT section with the Spin tool. If you use BST instead of the Spin tool you can use the @@@ operator to get absolute addresses. However, you're code will not compile under the Spin tool if you do this. With BST, your code would look like this:

L1 long @@@L2, <data>
L2 long @@@L3, <data>
L3 long @@@L1, <data>

msrobots

You could work with offsets instead of addresses

DAT
ORG 0
Begin mov Ptr,par
         mov FirstPtr,par ' keep Address of First element

         rdlong NextPtr,Ptr ' Save the offset of link 
         add NextPtr,FirstPtr    ' add Address of first element to get Hubaddress in NextPtr

         add Ptr,#4 ' Point to the data
do whatever

having your List with offsets instead of Addresses

L1 long @L2-@L1, <data>
L2 long @L3-@L1, <data>
L3 Long @L1-@L1, <data>

Enjoy!

Mike