+++ /dev/null
-A Few Notes on the New Object Processor Assembler
--------------------------------------------------
-
-Q: What is it?
-
-A: An assembler to generate object lists for the Atari Jaguar's Object
- processor.
-
-
-Q: Why is it here?
-
-A: To really utilize the OP properly, it needs an assembler. Otherwise, what
- happens is you end up writing an assembler in your code to assemble the OP
- list, and that's a real drag--something that *should* be handled by a proper
- assembler.
-
-
-Q: How do I use it?
-
-A: The OP assembler works similarly to the RISC assembler; to enter the OP
- assembler, you put the .objproc directive in your code (N.B.: like the RISC
- assembler, it only works in a TEXT or DATA section). From there, you build
- the OP list how you want it and go from there. A few caveats: you will want
- to put a .org directive at the top of your list, and labels that you want to
- be able to address in 68xxx code (for moving from a data section to an
- address where it will be executed by the OP, for example) should be created
- in .68xxx mode.
-
-
-Q: What are the opcodes?
-
-A: They are bitmap, scbitmap, gpuobj, branch, stop, nop, and jump. nop and jump
- are psuedo-ops, they are there as a convenience to the coder.
-
-
-Q: What are the proper forms for these opcodes?
-
-A: They are as follows:
-
- bitmap <data addr>, <xloc>, <yloc>, <dwidth>, <iwidth>, <iheight>, <bpp>,
- <pallete idx>, <flags>, <firstpix>, <pitch>
- scbitmap <data addr>, <xloc>, <yloc>, <dwidth>, <iwidth>, <iheight>,
- <xscale>, <yscale>, <remainder>, <bpp>, <pallete idx>,
- <flags>, <firstpix>, <pitch>
- gpuobj <line #>, <userdata> (bits 14-63 of this object)
- branch VC <condition (<, =, >)> <line #>, <link addr>
- branch OPFLAG, <link addr>
- branch SECHALF, <link addr>
- stop
- nop
- jump <link addr>
-
- Note that the <flags> field in bitmap and scbitmap objects consist of the
- following: REFLECT, RMW, TRANS, RELEASE. They can be in any order (and
- should be separated by whitespace *only*), and you can only put a maximum of
- four of them in. Further note that with bitmap and scbitmap objects, all the
- parameters after <data addr> are optional--if they are omitted, they will
- use defaults (mostly 0, but 1 is the default for pitch). Also, in the
- scbitmap object, the <xscale>, <yscale>, and <remainder> fields can be
- floating point constants/expressions. <data addr> can refer to any address
- defined (even external!) and the linker (rln v1.6.0 or greater) will
- properly fix up the address.
-
-
-Q: What do they do?
-
-A: Pretty much what you expect. It's beyond the scope of this little note to
- explain the Jaguar's Object Processor and how it operates, so you'll have to
- seek explanations for how they work elsewhere.
-
-
-Q: Why do I want to put a .org directive at the top of my list?
-
-A: You want to put a .org directive at the top of your list because otherwise
- the assembler will not know where in memory the object list is supposed
- go--then when you move it to its destination, the object link addresses will
- all be wrong and it won't work.
-
-
-Q: Why would I copy my object list to another memory location?
-
-A: Simple: because the OP destroys the list as it uses it to render the screen.
- If you don't keep a fresh copy stashed away somewhere to refresh it before
- the next frame is rendered, what you see on the screen will not be what you
- expect, as the OP has scribbled all over it!
-
-
-Q: Does the assembler do anything behind my back?
-
-A: Yes, it will emit NOPs to ensure that bitmaps and scbitmaps are on proper
- memory boundaries, and fixup link addresses as necessary. This is needed
- because of a quirk in how the OP works (it ORs constants on the address
- lines to get the phrases it needs and if they are not zeroes, it will fail
- in bizarre ways). It will also set all <ypos> constants on the correct
- half-line (as that's how the OP views them).
-
-
-Q: Why can't I define the link addresses for all the objects?
-
-A: You really, *really* don't want to do this. Trust me on this one.
-
-
-Q: How about an example of an object list?
-
-A: Here you go:
-
- objList = $10000
- bRam = $20000
-;
- .68000
-objects: ; This is the label you will use to address this in 68K code
- .objproc ; Engage the OP assembler
- .org objList ; Tell the OP assembler where the list will execute
-;
- branch VC < 69, .stahp ; Branch to the STOP object if VC < 69
- branch VC > 241, .stahp ; Branch to the STOP object if VC > 241
- bitmap bRAM, 22, 70, 24, 24, 22, 4
- bitmap bRAM, 20+96+96, 70, 24, 24, 22, 4, 0, REFLECT
- scbitmap tms, 20, 70, 1, 1, 8, 3.0, 3.0, 2.9999, 0, 0, TRANS
- scbitmap tmsShadow, 23, 73, 1, 1, 8, 3.0, 3.0, 2.9999, 0, 3, TRANS
- bitmap sbRelBM, 30, 108, 3, 3, 8, 0, 1, TRANS
- bitmap txt1BM, 46, 132, 3, 3, 8, 0, 2, TRANS
- bitmap txt2BM, 46, 148, 3, 3, 8, 0, 2, TRANS
- bitmap txt3BM, 22, 164, 3, 3, 8, 0, 2, TRANS
- jump .haha
-.stahp:
- stop
-.haha:
- jump .stahp
-
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