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Annotation of uae/docs/README.PROGRAMMERS, revision 1.1.1.10

1.1 root 1: You can help to make this program better. If you fix bugs or implement new
2: features, I'd be grateful if you send me patches. For a list of interesting
3: projects, and for a brief summary on how UAE works, see below.
4:
5: A few guidelines for anyone who wants to help:
6: - Please contact me first before you implement major new features. Someone
7: else might be doing the same thing already. This has already happened :-(
8: Even if no one else is working on this feature, there might be alternative
9: and better/easier/more elegant ways to do it.
10: - If you have more than one Kickstart, try your code with each one.
11: - Patches are welcome in any form, but diff -u or diff -c output is preferred.
12: If I get whole source files, the first thing I do is to run diff on it. You
13: can save me some work here (and make my mailbox smaller).
14:
15: Some possible projects, in order of estimated difficulty:
1.1.1.2 root 16: - Add gamma correction
1.1.1.3 root 17: - If the serial port still isn't working (I've got no idea, I don't use it),
18: fix it.
1.1 root 19: - Someone with a 68020 data sheet might check whether all opcodes are
20: decoded correctly and whether all instructions really do what they are
21: supposed to do (I'm pretty sure it's OK by now, but you never know...).
1.1.1.3 root 22: - Add more 2.0 packets to filesys.c
1.1.1.2 root 23: - Multi-thread support is there now, it just needs someone to test it on a SMP
24: machine and to fix it so it improves speed instead of slowing the thing
25: down.
1.1 root 26: - Improve the Kickstart replacement to boot more demos.
27: - Snapshots as in CPE. Will need to collect all the variables containing
28: important information. Fairly easy, but boring. (Use core dumps instead :-)
1.1.1.2 root 29: _If_ someone attempts this, please be more clever than the various CPC
30: emulators and dump state only at one fixed point in the frame, preferrably
1.1.1.3 root 31: the vsync point. Also talk with Petter about this.
1.1 root 32: - Find out why uae.device has to be mounted manually with Kick 1.3.
33: The problem seems to be that we don't have a handler for it. I _think_ what
34: we need is the seglist of the standard filesystem handler. Problem is,
35: DOS hasn't been started when the devices are initialized and so we can't get
36: to the DosBase->RootNode->FileHandlerSeg pointer, and then there is the
37: confusing matter of BCPL GlobVecs and other weird stuff...
1.1.1.2 root 38: - Some incompatibilities might be fixed with user-modifiable fudge variables
39: the same way it's done in various C64 emulators.
40: - With the new display code, it would probably be easier than before to
41: implement ECS resolutions - however, a lot of places rely on the OCS timing
42: parameters and display sizes.
1.1 root 43: - Figure out a diskfile format that supports every possible non-standard
1.1.1.6 root 44: format [I'll work on this soon (I hope)].
45: - Port bsdsocket library code to other operating systems than Win32.
1.1 root 46: - Implement 68551 MMU. I have docs now. Not among the most necessary things.
1.1.1.3 root 47: Should be done like exception 3 handling: add code to genamode in gencpu.c.
1.1 root 48: - Implement AGA support. Some bits and pieces exist.
49: - Reimplement Amiga OS. (Well-behaved) Amiga programs could then be made
50: to use the X Window System as a "public screen". Of course, not all the
1.1.1.3 root 51: OS would have to be re-done, only Intuition/GFX/Layers (which is enough).
52: [Started, look at gfxlib.c - not usable yet.]
1.1.1.2 root 53: - Find some extremely clever ways to optimize the smart update methods. Some
54: ideas:
55: a) Always use memcmpy() to check for bitplane differences. If no differences
56: are found, see if BPLxDELAY got modified, if so, scroll.
1.1.1.3 root 57: Problems:
1.1.1.2 root 58: * You'd still have to draw a few pixels around the DIW borders. Not very
59: hard.
60: * Scrolling with memcpy in video memory can be terribly slow (no, I
61: shouldn't have bought the cheaper video card with DRAMs)
62: * At least every 15 pixels a full update has to be done since the
63: bitplane pointers get updated after that. And that's with the slowest
64: scrolling - if the playfield scrolls faster, the benefit converges
65: against zero.
66: You could also do vertical scrolling tests, but similar problems arise -
67: where should one check? One line above/below? What about faster
68: scrolling? You could use the bitplane pointers as hints, but with
69: double/triple buffering this gets problematic, too.
70: On the whole, I don't think it would be worth the effort, even if it
71: works very well for a few games.
72: b) Well, there is no b). If I thought of something I forgot it while
73: writing a).
1.1 root 74: - Port it to Java and Emacs Lisp
75: - A formal proof of correctness would be nice.
76:
77:
1.1.1.3 root 78: Source file layout
79:
80: src/ contains (mostly) machine-independent C code.
81: include/ contains header files included by C code.
82: md-*/ CPU and compiler dependent files, linked to machdep by configure
83: od-*/ operating system dependent files, linked to osdep by configure
84: td-*/ thread library dependent files, linked to threaddep by configure
85: sd-*/ Sound code. sd-* is only for sound systems which are not OS specific
86: or for which no "od-*" directory exists. Linked to sounddep
1.1.1.7 root 87: scg-*/ SCSI code.
88: This is the same code as in the cdrecord libscg, so this will become
89: obsolete as soon as the libscg is released seperately. In the meantime,
90: UAE will be distributed together with the code itself, because it
91: also requires patching: not every libscg implementation is thread-safe
92: in the current cdrecord version.
1.1.1.3 root 93: targets/ Contains header files which contain some information about which
94: options a specific port of UAE understands.
95:
96:
97: Coding style
98:
99: As long as your code is hidden in a file buried in md-*/ or od-*/ where I
100: never have a look at it, you can probably get away with not following these
101: guidelines.
102:
103: * Do not include CR characters.
104: * Do not use GNU C extensions if you can't hide them in a macro or in a
105: system-specific file so that an alternative implementation is available
106: when GNU C is not used.
107: This applies to _all_ OS/CPU/compiler specific details. Basically, nothing
108: of that sort should appear in src/*.c (we're a bit away from that goal at
109: the moment, but it's getting better).
1.1.1.8 root 110: * Repeat after me: #ifdefs are evil (most of the time).
1.1.1.3 root 111: * Make sure your code does not make assumption about type sizes other than
112: the minimum widths allowed by C. If you need specific type sizes, use the
113: uae_u32 type and its friends.
114: * Set up your editor so that tab characters round up to the next position
115: where ((cursorx-1) % 8) == 0, i.e. 8 space tabs. Do not use 4 space tabs,
116: that makes the code awful to read on other machines and worse to edit.
1.1.1.5 root 117: (I'm talking about the tab character here, not indentation!)
1.1.1.3 root 118: * Lines can be up to 132 characters wide. Use SVGATextMode for the Linux
119: console, or use a windowing system in a high resolution.
120: * C++ comments are a no-no in C code.
121: * Indentation - look at some code in custom.c and try to follow it. Don't
122: use GNU 2-space-in-weird-places indentation, I find it awful. But _do_
123: follow the GNU rules for adding whitespace in expressions, and those for
124: breaking up multiple-line if statements.
125: Fixed indentation rules almost never make sense - break the rules if that
126: makes your code more readable.
127: Hint: Get jed from space.mit.edu, /pub/davis. It can indent your code
128: automatically. Put the following into your .jedrc, and it will come out
129: right:
130: C_INDENT = 4;
131: C_BRACE = 0;
132: C_BRA_NEWLINE = 0;
133: C_Colon_Offset = 1;
134: C_CONTINUED_OFFSET = 4;
135:
136:
1.1 root 137: How it works
138:
139: Let's start with the memory emulation. All addressable memory is split into
140: banks of 64K each. Each bank can define custom routines accessing bytes,
141: words, and longwords. All banks that really represent physical memory just
142: define these routines to write/read the specified amount of data to a chunk
1.1.1.3 root 143: of memory. This memory area is organized as an array of uae_u8, which means
1.1 root 144: that those parts of the emulator that want to access memory in a linear
1.1.1.3 root 145: fashion can get a (uae_u8 *) pointer and use it to circumvent the overhead of
1.1.1.2 root 146: the put_*() and get_*() calls. That is done, for example, in the
1.1 root 147: pfield_doline() function which handles screen refreshes.
148: Memory banks that represent hardware registers (such as the custom chip bank
149: at 0xDF0000) can trap reads/writes and take any necessary actions.
150:
151: To provide a good emulation of graphical effects, only one thing is vital:
152: Copper and playfield emulation have to be kept absolutely synchronous. If the
153: copper writes to (say) a color register in a specific cycle, the playfield
1.1.1.2 root 154: hardware needs to use the new information in the next word of data it
1.1 root 155: processes.
156: UAE 0.1 used to call routines like do_pfield() and do_copper() each time the
157: CPU emulator had finished an instruction. That was one of the reasons why it
158: was so slow. Recent versions try to draw complete scanlines in one piece. This
159: is possible if the copper does not write to any registers affecting the
160: display during that scanline. Therefore, drawing the line is deferred until
1.1.1.2 root 161: the last cycle of the line. However, sometimes a register which affects how
162: the screen will look is modified before the end of the line (think of copper
163: plasmas). That's what "struct decision thisline_decision" is for. It is
164: initialized at the start of each line. During the line, whenever a vital
165: register is changed, one of the decide_*() functions is called and may modify
166: thisline_decision. There are several independent decisions:
167: - which DIW should be used
168: - where does data fetch start/stop (or is the line in the border altogether)
169: - where should sprites be drawn (note: the same sprite can appear more than
170: once on one scanline, see Turrican I world 3 levels 1 and 3 for the best
171: example)
172: - what are the playfield pointers at the start of DDF. Related, what data do
173: they point to.
174: - what are the playfield modulos at the end of DDF
175: - coppermagic with the colors is remembered for later use
176: - so is copper magic with the bitplane delay values. I used to think there
177: was no useful application for modifying BPLCON1 while data is being
178: displayed, but Sanity demos can make Amiga emulator programmers look real
179: old.
180:
181: All of this is remembered while the raster line is processed by the hardware.
182: After the line (at hsync), all the decisions are made if they weren't made
183: before. At that point the line can be drawn by playfield_draw_line.
184: Additionally, all the decisions from the previous displayed frame are saved
185: and compared with the new ones, since often lines are not modified between
186: frames. This saves a lot of redrawing work.
1.1 root 187:
188: The CPU emulator no longer has to call all sorts of functions after each
189: instruction. Instead, it keeps a list of events that are scheduled (timer
190: interrupts, hsync and vsync events) and their "arrival time". Only the time
191: for the next event is checked after each CPU instruction. If it's higher than
192: the current cycle counter, the CPU can continue to execute.
193:
1.1.1.2 root 194: Things that can't be supported with the current "decision" model:
195: - Changes in lores/hires mode during one line. Dunno whether that was ever
196: used in reality.
197: - Changes to the bitplane DMA bit during one line. Hardly useful and not
1.1.1.3 root 198: likely to be used. [but there are at least two programs which do ugly
1.1.1.2 root 199: things like that, and there are some hacks in UAE that make those programs
200: work (Magic 12 Ray of Hope 2 is one of these demos)]
201: - Changes in bitplane data during one line. If programs do this kind of
202: thing, it's most likely accidental and the program is broken. Can happen
203: with programs that use the blitter incorrectly, like all the Andromeda
204: demos.
205: - others? (fill in if you can think of anything)
206:
207: All in all, it's unlikely that this causes compatibility problems. If it does,
208: fudge values could be introduced (although that sort of thing gets messy
209: quickly).
1.1 root 210:
211:
1.1.1.3 root 212: * Native code vs. 68k code
1.1.1.2 root 213:
1.1.1.3 root 214: It is possible to call native code from 68k code; autoconf.c has some routines
215: which make setting up a call trap very easy. However, it is not as easy to
216: call 68k code from native C code, at least not while Amiga Exec multitasking
217: is running. You ask why?
218:
219: Amiga process1 calls native function foo
220: Native function foo calls some 68k function and goes into 68k mode
221: Amiga context switch happens, process1 is put to sleep and process2 gets run.
222: Amiga process2 calls native function foo
223: Native function foo calls some 68k function and goes into 68k mode
224: Amiga context switch happens, process2 is put to sleep and process1 gets run.
225: Process 1 completes the 68k function called by foo and returns from 68k mode.
226:
227: There. Now we are in function foo again. When it called the 68k code, process2
228: was active. Now process1 is active, and the function we called in process2
229: hasn't completed yet. What a mess.
230:
231: To get around this, you need to do some stack magic. Code to do this exists,
232: but it must be adapted for each port, since setting up a different stack is
233: completely non-portable.
234:
235:
236: * How multithreading in filesys.c works
237:
238: AmigaOS is nice enough to start one processes for each mounted filesystem. All
239: of these run in the 68k emulation code, i.e. in the main UAE thread. This is
240: the reason why multithreading is desirable: if the main UAE thread blocks
241: waiting for I/O, the CPU emulation can't continue to run. Since the Amiga OS
242: is capable of multi-tasking, it is possible that other code could run until
243: the I/O operation is complete. The most important bit of code that can run is
244: the code that moves the mouse pointer - it's unpleasant if the pointer does
245: not follow mouse movement during disk/CD accesses.
246:
247: When a packet is received by the filesys.asm code, filesys_handler is called.
248: This function always runs in the main UAE thread.
249: - In the single-threaded case, this function performs the action that was
250: requested, then returns 0 to indicate "action completed, reply packet".
251: Nothing else is performed.
252: - In the multi-threaded case, filesys_handler figures out which unit the
253: packet was for and sends the packet to the UAE thread responsible for
254: handling this unit. filesys_handler returns 0 to indicate: queue the
255: packet. Also, one (at that point unused) field in the packet is set to
256: 0 to indicate that the action was not completed.
257:
258: The latter case is the interesting one. The thread that got the packet does
259: the following:
260: - perform the action as usual
261: - set the "command complete" field in the packet to -1.
262: - send a message to the AmigaOS (!) filesystem process. However, it can't do
263: that without some effort. We can't call 68k code from the emulator easily.
264: So we have to use an Amiga interrupt. The filesystem init code sets up an
265: Exec IntServer for the EXTER interrupt, and hsync_handler() checks
266: periodically whether the filesystem needs an interrupt and raises one if
267: necessary.
268: Only one dummy message is used per filesystem unit, which is allocated at
269: startup. This means that there must be some locking to prevent the unit
270: thread from sending the same message twice to the same port. To determine
271: whether the message is free, three counts are kept. "cmds_sent" is
272: incremented by the UAE thread whenever it has completed a command.
273: "cmds_acked" is set to the same value of cmds_sent at the point that the
274: interrupt handler got invoked and decided it must send a message. Finally,
275: cmds_complete is set to this value at the time the AmigaOS process receives
276: the dummy message. Whenever cmds_acked == cmds_complete, the dummy message
277: is free to be sent again.
278:
279: The EXTER interrupt basically walks through the units, looks at the cmds_*
280: fields and sends the dummy message to the Amiga filesystem process when
281: possible and necessary.
282:
283: When the Amiga filesystem process receives such a dummy message, it does the
284: following:
285: - increment cmds_complete as described above.
286: - walk through the queue of unprocessed commands and see which ones now have
287: a status of -1, indicating that they are finished. These are removed from
288: the queue and replied to.
289:
290:
291: * Calltraps at fixed locations
292:
293: F0FF00: return from 68k mode.
294: F0FF10: must have gotten lost somewhere ;)
295: F0FF20: used by filesys.c to store away some information from the startup
296: packet.
297: F0FF30: filesys_handler().
298: F0FF40: startup_handler(), handles only the startup packet for each
299: filesystem.
300: F0FF50: used by the EXTER interrupt which we set up for the filesystem.
301: F0FF60: used by the uaectrl/uae-control programs (see uaelib.c)
302: F0FF70: used by the task that gets set up for the mouse emulation.
1.1.1.7 root 303: F0FF80: getchipmemsize()
304: F0FF90: uaeexe
305: F0FFA0: timehack
1.1.1.9 root 306: F0FFB0: AHI
1.1.1.10! root 307: F0FFC0: infinite loop used in an emergency.
1.1.1.5 root 308:
1.1.1.3 root 309: * How the compiler works
1.1.1.2 root 310:
311: .. yet to be written. To be decided, in fact.
1.1.1.3 root 312:
313:
314: Portability
315:
316: This section was out of date. I'll rewrite it.
317: Some day.

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