mirror of
https://github.com/irmen/prog8.git
synced 2024-12-25 23:29:55 +00:00
278 lines
15 KiB
ReStructuredText
278 lines
15 KiB
ReStructuredText
=================
|
|
Technical details
|
|
=================
|
|
|
|
All variables are static in memory
|
|
----------------------------------
|
|
|
|
All variables are allocated statically, there is no concept of dynamic heap or stack frames.
|
|
Essentially all variables are global (but scoped) and can be accessed and modified anywhere,
|
|
but care should be taken of course to avoid unexpected side effects.
|
|
|
|
Especially when you're dealing with interrupts or re-entrant routines: don't modify variables
|
|
that you not own or else you will break stuff.
|
|
|
|
Variables that are not put into zeropage, will be put into a special 'BSS' section for the assembler.
|
|
This section is usually placed at the end of the resulting program but because it only contains empty space
|
|
it won't actually increase the size of the resulting program binary.
|
|
Prog8 takes care of properly filling this memory area with zeros at program startup and then reinitializes
|
|
the subset of variables that have a nonzero initialization value.
|
|
|
|
Arrays with initialization values are not put into BSS but just occupy a sequence of bytes in
|
|
the program memory: their values are not reinitialized at program start.
|
|
|
|
It is possible to relocate the BSS section using a compiler option
|
|
so that more system ram is available for the program code itself.
|
|
|
|
|
|
.. _banking:
|
|
|
|
ROM/RAM bank selection
|
|
----------------------
|
|
|
|
On certain systems prog8 provides support for managing the ROM or RAM banks that are active.
|
|
|
|
======= ============================================= ===========
|
|
system get banks (returns byte) set banks
|
|
======= ============================================= ===========
|
|
c64 ``c64.getbanks()`` ``c64.banks(x)``
|
|
c128 ``c128.getbanks()`` ``c128.banks(x)``
|
|
cx16 ``cx16.getrombank()`` , ``cx16.getrambank()`` ``cx16.rombank(x)`` , ``cx16.rambank(x)``
|
|
other N/A N/A
|
|
======= ============================================= ===========
|
|
|
|
Calling a subroutine in another memory bank can be done by using the ``callfar`` or ``callfar2`` builtin functions.
|
|
|
|
When you are using the routines above, you are doing explicit manual banks control.
|
|
However, Prog8 also provides something more sophisticated than this, when dealing with banked subroutines:
|
|
|
|
External subroutines defined with ``extsub`` can have a non-standard ROM or RAM bank specified as well.
|
|
The compiler will then transparently change a call to this routine so that the correct bank is activated
|
|
automatically before the normal jump to the subroutine (and switched back on return). The programmer doesn't
|
|
have to bother anymore with setting/resetting the banks manually, or having the program crash because
|
|
the routine is called in the wrong bank! You define such a routine by adding ``@bank <bank>``
|
|
to the extsub subroutine definition. This specifies the bank number where the subroutine is located in.
|
|
You can use a constant bank number 0-255, or a ubyte variable to make it dynamic::
|
|
|
|
extsub @bank 10 $C09F = audio_init()
|
|
extsub @bank banknr $A000 = first_hiram_routine()
|
|
|
|
When you then call this routine in your program as usual, the compiler will no longer generate a simple JSR instruction to the
|
|
routine. Instead it will generate a piece of code that automatically switches the ROM or RAM bank to the
|
|
correct value, does the call, and switches the bank back. The exact code will be different for different
|
|
compilation targets, and not all targets even have banking or support this. As an example,
|
|
on the Commander X16, prog8 will use the JSRFAR kernal routine for this. On the Commodore 128,
|
|
a similar call exists (but requires a lot more code to prepare, so beware).
|
|
On the Commodore 64 some custom code is also emitted that toggle the banks, retains some registers, and does the call.
|
|
Other compilation targets don't have banking or prog8 doesn't yet support automatic bank selection on them.
|
|
|
|
There's a "banking" example for the Commander X16 that shows a possible application
|
|
of the extsub with bank support, check out the `bank example code <https://github.com/irmen/prog8/tree/master/examples/cx16/banking>`_ .
|
|
|
|
|
|
Notice that the symbol for this routine in the assembly source code will still be defined as usual.
|
|
The bank number is not translated into assembly (only as a comment)::
|
|
|
|
p8s_audio_init = $c09f ; @bank 10
|
|
|
|
.. caution::
|
|
Calls with automatic bank switching like this are not safe to use from IRQ handlers. Don't use them there.
|
|
Instead change banks in a controlled manual way (or not at all).
|
|
|
|
.. note::
|
|
On the C64 and C128, the Basic ROM is *banked out* by default when running a Prog8 program, because
|
|
it is not needed. This means on the C64 we get access to another 8Kb of RAM at that
|
|
memory area, which actually gives us a 50 Kb contiguous RAM block from $0801 to $d000 (exclusive).
|
|
This means you can create programs of up to **50 Kb** size with prog8 on the C64.
|
|
On the C128, it means programs can use ~41 Kb of contiguous RAM at $1c00 to $c000 (exclusive).
|
|
However, if your program uses floats, Prog8 *does* need the Basic ROM for the floating point routines,
|
|
and it won't be banked out. Such programs are limited to the regular size of about 38 Kb on the C64, and less on the C128.
|
|
Be aware that the bank setting is only done if you are *not* using ``%option no_sysinit`` because the
|
|
program's bootstrap code is what initializes the memory bank configuration.
|
|
|
|
|
|
.. _symbol-prefixing:
|
|
|
|
Symbol prefixing in generated Assembly code
|
|
-------------------------------------------
|
|
|
|
*All* symbols in the prog8 program will be prefixed in the generated assembly code:
|
|
|
|
============ ========
|
|
Element type prefix
|
|
============ ========
|
|
Block ``p8b_``
|
|
Subroutine ``p8s_``
|
|
Variable ``p8v_``
|
|
Constant ``p8c_``
|
|
Label ``p8l_``
|
|
other ``p8_``
|
|
============ ========
|
|
|
|
This is to avoid naming conflicts with CPU registers, assembly instructions, etc.
|
|
So if you're referencing symbols from the prog8 program in inlined assembly code, you have to take
|
|
this into account. Stick the proper prefix in front of every symbol name component that you want to reference that is coming
|
|
from a prog8 source file.
|
|
All elements in scoped names such as ``main.routine.var1`` are prefixed so this becomes ``p8b_main.p8s_routine.p8v_var1``.
|
|
|
|
.. attention::
|
|
Symbols from library modules are *not* prefixed and can be used
|
|
in assembly code as-is. So you can write::
|
|
|
|
%asm {{
|
|
lda #'a'
|
|
jsr cbm.CHROUT
|
|
}}
|
|
|
|
|
|
Subroutine Calling Convention
|
|
-----------------------------
|
|
|
|
Calling a subroutine requires three steps:
|
|
|
|
#. preparing the arguments (if any) and passing them to the routine.
|
|
Numeric types are passed by value (bytes, words, booleans, floats),
|
|
but array types and strings are passed by reference which means as ``uword`` being a pointer to their address in memory.
|
|
#. calling the subroutine
|
|
#. preparing the return value (if any) and returning that from the call.
|
|
|
|
|
|
Regular subroutines
|
|
^^^^^^^^^^^^^^^^^^^
|
|
|
|
- Each subroutine parameter is represented as a variable scoped to the subroutine. Prog8 doesn't have a call stack.
|
|
- The arguments passed in a subroutine call are evaluated by the caller, and then put into those variables by the caller.
|
|
The order of evaluation of subroutine call arguments *is unspecified* and should not be relied upon.
|
|
- The subroutine is invoked.
|
|
- The return value is not put into a variable, but the subroutine passes it back to the caller via register(s):
|
|
|
|
- A byte value will be put in ``A`` .
|
|
- A boolean value will be put in ``A`` too, as 0 or 1.
|
|
- A word value will be put in ``A`` + ``Y`` register pair (lsb in A, msb in Y).
|
|
- A float value will be put in the ``FAC1`` float 'register'.
|
|
|
|
**Builtin functions can be different:**
|
|
some builtin functions are special and won't exactly follow these rules.
|
|
|
|
**Some arguments will be passed in registers:**
|
|
For single byte and word arguments, the values are simply loaded in cpu registers by the caller before calling the subroutine.
|
|
*The subroutine itself will take care of putting the values into the parameter variables.* This saves on code size because
|
|
otherwise all callers would have to store the values in those variables themselves.
|
|
Note that his convention is also still used for subroutines that specify parameters to be put into
|
|
one of the *virtual registers* R0-R15, as those are in the end just variables too.
|
|
The rules are as follows:
|
|
|
|
Single byte parameter: ``sub foo(ubyte bar) { ... }``
|
|
gets bar in the accumulator A, *subroutine* stores it into parameter variable
|
|
|
|
Two byte parameters: ``sub foo(ubyte bar, ubyte baz) { ... }``
|
|
gets bar in the accumulator A, and baz in Y, *subroutine* stores it into parameter variable
|
|
|
|
Single word parameter: ``sub foo(uword bar) { ... }``
|
|
gets bar in the register pair A + Y (lsb in A, msb in Y), *subroutine* stores it into parameter variable
|
|
|
|
Floating point parameter: ``sub foo(float bar) { ... }``
|
|
value for bar gets copied into the parameter variable *by the caller*
|
|
|
|
Other: ``sub foo(ubyte bar, ubyte baz, ubyte zoo) { ... }``
|
|
register values indeterminate, values all get stored in the parameter variables *by the caller*
|
|
|
|
|
|
|
|
``asmsub`` and ``extsub`` routines
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
These are kernal (ROM) routines or low-level assembly routines, that get their arguments via specific registers.
|
|
Sometimes even via a processor status flag such as the Carry flag.
|
|
Note that word values can be put in a "CPU register pair" such as AY (meaning A+Y registers) but also
|
|
in one of the 16 'virtual' 16 bit registers introduced by the Commander X16, R0-R15.
|
|
Float values can be put in the FAC1 or FAC2 floating point 'registers'.
|
|
The return values also get returned via designated registers, or via processor status flags again.
|
|
This means that after calling such a routine you can immediately act on the status
|
|
via a special branch instruction such as ``if_z`` or ``if_cs`` etc.
|
|
The register/status flag usage is fully specified in the asmsub or extsub signature defintion
|
|
for both the parameters and the return values::
|
|
|
|
extsub $2000 = extfunction(ubyte arg1 @A, uword arg2 @XY, uword arg3 @R0,
|
|
float frac @FAC1, bool flag @Pc) -> ubyte @Y, bool @Pz
|
|
|
|
asmsub function(ubyte arg1 @A, uword arg2 @XY, uword arg3 @R0,
|
|
float frac @FAC1, bool flag @Pc) -> ubyte @Y, bool @Pz {
|
|
%asm {{
|
|
...
|
|
...
|
|
}}
|
|
}
|
|
|
|
|
|
Compiler Internals
|
|
------------------
|
|
|
|
Here is a diagram of how the compiler translates your program source code into a binary program:
|
|
|
|
.. image:: prog8compiler.svg
|
|
|
|
Some notes and references into the compiler's source code modules:
|
|
|
|
#. The ``compileProgram()`` function (in the ``compiler`` module) does all the coordination and basically drives all of the flow shown in the diagram.
|
|
#. ANTLR is a Java parser generator and is used for initial parsing of the source code. (``parser`` module)
|
|
#. Most of the compiler and the optimizer operate on the *Compiler AST*. These are complicated
|
|
syntax nodes closely representing the Prog8 program structure. (``compilerAst`` module)
|
|
#. For code generation, a much simpler AST has been defined that replaces the *Compiler AST*.
|
|
Most notably, node type information is now baked in. (``codeCore`` module, Pt- classes)
|
|
#. An *Intermediate Representation* has been defined that is generated from the intermediate AST. This IR
|
|
is more or less a machine code language for a virtual machine - and indeed this is what the built-in
|
|
prog8 VM will execute if you use the 'virtual' compilation target and use ``-emu`` to launch the VM.
|
|
(``intermediate`` and ``codeGenIntermediate`` modules, and ``virtualmachine`` module for the VM related stuff)
|
|
#. The code generator backends all implement a common interface ``ICodeGeneratorBackend`` defined in the ``codeCore`` module.
|
|
Currently they get handed the program Ast, Symboltable and several other things.
|
|
If the code generator wants it can use the ``IRCodeGen`` class from the ``codeGenIntermediate`` module
|
|
to convert the Ast into IR first. The VM target uses this, but the 6502 codegen doesn't right now.
|
|
|
|
|
|
Run-time memory profiling with the X16 emulator
|
|
-----------------------------------------------
|
|
The X16 emulator has a ``-memorystats`` option that enables it to keep track of memory access count statistics,
|
|
and write the accumulated counts to a file on exit.
|
|
Prog8 includes a Python script ``profiler.py`` (find it in the "scripts" subdirectory of the source code distribution)
|
|
that can cross-reference that file with an assembly listing produced by the compiler with the ``-asmlist`` option.
|
|
It then prints the top N lines in your (assembly) program source that perform the most reads and writes,
|
|
which you can use to identify possible hot spots/bottlenecks/variables that should be better placed in zeropage etc.
|
|
Note that the profiler just works with the number of accesses to memory locations, this is *not* the same
|
|
as the most run-time (cpu instructions cycle times aren't taken into account at all).
|
|
Here is an example of the output it generates::
|
|
|
|
$ scripts/profiler.py -n 10 cobramk3-gfx.list memstats.txt ✔
|
|
|
|
number of actual lines in the assembly listing: 2134
|
|
number of distinct addresses read from : 22006
|
|
number of distinct addresses written to : 8179
|
|
total number of reads : 375106285 (375M)
|
|
total number of writes : 63601962 (63M)
|
|
|
|
top 10 most reads:
|
|
$007f (7198687) : $007e 'P8ZP_SCRATCH_W2' (line 13), $007e 'remainder' (line 1855)
|
|
$007e (6990527) : $007e 'P8ZP_SCRATCH_W2' (line 13), $007e 'remainder' (line 1855)
|
|
$0265 (5029230) : unknown
|
|
$007c (4455140) : $007c 'P8ZP_SCRATCH_W1' (line 12), $007c 'dividend' (line 1854), $007c 'result' (line 1856)
|
|
$007d (4275195) : $007c 'P8ZP_SCRATCH_W1' (line 12), $007c 'dividend' (line 1854), $007c 'result' (line 1856)
|
|
$0076 (3374800) : $0076 'label_asm_35_counter' (line 2082)
|
|
$15d7 (3374800) : $15d7 '9c 23 9f stz cx16.VERA_DATA0' (line 2022), $15d7 'label_asm_34_repeat' (line 2021)
|
|
$15d8 (3374800) : $15d7 '9c 23 9f stz cx16.VERA_DATA0' (line 2022), $15d7 'label_asm_34_repeat' (line 2021)
|
|
$15d9 (3374800) : $15da '9c 23 9f stz cx16.VERA_DATA0' (line 2023)
|
|
$15da (3374800) : $15da '9c 23 9f stz cx16.VERA_DATA0' (line 2023)
|
|
|
|
top 10 most writes:
|
|
$9f23 (14748104) : $9f23 'VERA_DATA0' (line 1451)
|
|
$0265 (5657743) : unknown
|
|
$007e (4464393) : $007e 'P8ZP_SCRATCH_W2' (line 13), $007e 'remainder' (line 1855)
|
|
$007f (4464393) : $007e 'P8ZP_SCRATCH_W2' (line 13), $007e 'remainder' (line 1855)
|
|
$007c (4416537) : $007c 'P8ZP_SCRATCH_W1' (line 12), $007c 'dividend' (line 1854), $007c 'result' (line 1856)
|
|
$007d (3820272) : $007c 'P8ZP_SCRATCH_W1' (line 12), $007c 'dividend' (line 1854), $007c 'result' (line 1856)
|
|
$0076 (3375568) : $0076 'label_asm_35_counter' (line 2082)
|
|
$01e8 (1310425) : cpu stack
|
|
$01e7 (1280140) : cpu stack
|
|
$0264 (1258159) : unknown
|
|
|
|
Apparently the most cpu activity while running this program is spent in a division routine.
|