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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
87: targets/ Contains header files which contain some information about which
88: options a specific port of UAE understands.
89:
90:
91: Coding style
92:
93: As long as your code is hidden in a file buried in md-*/ or od-*/ where I
94: never have a look at it, you can probably get away with not following these
95: guidelines.
96:
97: * Do not include CR characters.
98: * Do not use GNU C extensions if you can't hide them in a macro or in a
99: system-specific file so that an alternative implementation is available
100: when GNU C is not used.
101: This applies to _all_ OS/CPU/compiler specific details. Basically, nothing
102: of that sort should appear in src/*.c (we're a bit away from that goal at
103: the moment, but it's getting better).
104: * Make sure your code does not make assumption about type sizes other than
105: the minimum widths allowed by C. If you need specific type sizes, use the
106: uae_u32 type and its friends.
107: * Set up your editor so that tab characters round up to the next position
108: where ((cursorx-1) % 8) == 0, i.e. 8 space tabs. Do not use 4 space tabs,
109: that makes the code awful to read on other machines and worse to edit.
1.1.1.5 root 110: (I'm talking about the tab character here, not indentation!)
1.1.1.3 root 111: * Lines can be up to 132 characters wide. Use SVGATextMode for the Linux
112: console, or use a windowing system in a high resolution.
113: * C++ comments are a no-no in C code.
114: * Indentation - look at some code in custom.c and try to follow it. Don't
115: use GNU 2-space-in-weird-places indentation, I find it awful. But _do_
116: follow the GNU rules for adding whitespace in expressions, and those for
117: breaking up multiple-line if statements.
118: Fixed indentation rules almost never make sense - break the rules if that
119: makes your code more readable.
120: Hint: Get jed from space.mit.edu, /pub/davis. It can indent your code
121: automatically. Put the following into your .jedrc, and it will come out
122: right:
123: C_INDENT = 4;
124: C_BRACE = 0;
125: C_BRA_NEWLINE = 0;
126: C_Colon_Offset = 1;
127: C_CONTINUED_OFFSET = 4;
128:
129:
1.1 root 130: How it works
131:
132: Let's start with the memory emulation. All addressable memory is split into
133: banks of 64K each. Each bank can define custom routines accessing bytes,
134: words, and longwords. All banks that really represent physical memory just
135: define these routines to write/read the specified amount of data to a chunk
1.1.1.3 root 136: of memory. This memory area is organized as an array of uae_u8, which means
1.1 root 137: that those parts of the emulator that want to access memory in a linear
1.1.1.3 root 138: fashion can get a (uae_u8 *) pointer and use it to circumvent the overhead of
1.1.1.2 root 139: the put_*() and get_*() calls. That is done, for example, in the
1.1 root 140: pfield_doline() function which handles screen refreshes.
141: Memory banks that represent hardware registers (such as the custom chip bank
142: at 0xDF0000) can trap reads/writes and take any necessary actions.
143:
144: To provide a good emulation of graphical effects, only one thing is vital:
145: Copper and playfield emulation have to be kept absolutely synchronous. If the
146: copper writes to (say) a color register in a specific cycle, the playfield
1.1.1.2 root 147: hardware needs to use the new information in the next word of data it
1.1 root 148: processes.
149: UAE 0.1 used to call routines like do_pfield() and do_copper() each time the
150: CPU emulator had finished an instruction. That was one of the reasons why it
151: was so slow. Recent versions try to draw complete scanlines in one piece. This
152: is possible if the copper does not write to any registers affecting the
153: display during that scanline. Therefore, drawing the line is deferred until
1.1.1.2 root 154: the last cycle of the line. However, sometimes a register which affects how
155: the screen will look is modified before the end of the line (think of copper
156: plasmas). That's what "struct decision thisline_decision" is for. It is
157: initialized at the start of each line. During the line, whenever a vital
158: register is changed, one of the decide_*() functions is called and may modify
159: thisline_decision. There are several independent decisions:
160: - which DIW should be used
161: - where does data fetch start/stop (or is the line in the border altogether)
162: - where should sprites be drawn (note: the same sprite can appear more than
163: once on one scanline, see Turrican I world 3 levels 1 and 3 for the best
164: example)
165: - what are the playfield pointers at the start of DDF. Related, what data do
166: they point to.
167: - what are the playfield modulos at the end of DDF
168: - coppermagic with the colors is remembered for later use
169: - so is copper magic with the bitplane delay values. I used to think there
170: was no useful application for modifying BPLCON1 while data is being
171: displayed, but Sanity demos can make Amiga emulator programmers look real
172: old.
173:
174: All of this is remembered while the raster line is processed by the hardware.
175: After the line (at hsync), all the decisions are made if they weren't made
176: before. At that point the line can be drawn by playfield_draw_line.
177: Additionally, all the decisions from the previous displayed frame are saved
178: and compared with the new ones, since often lines are not modified between
179: frames. This saves a lot of redrawing work.
1.1 root 180:
181: The CPU emulator no longer has to call all sorts of functions after each
182: instruction. Instead, it keeps a list of events that are scheduled (timer
183: interrupts, hsync and vsync events) and their "arrival time". Only the time
184: for the next event is checked after each CPU instruction. If it's higher than
185: the current cycle counter, the CPU can continue to execute.
186:
1.1.1.2 root 187: Things that can't be supported with the current "decision" model:
188: - Changes in lores/hires mode during one line. Dunno whether that was ever
189: used in reality.
190: - Changes to the bitplane DMA bit during one line. Hardly useful and not
1.1.1.3 root 191: likely to be used. [but there are at least two programs which do ugly
1.1.1.2 root 192: things like that, and there are some hacks in UAE that make those programs
193: work (Magic 12 Ray of Hope 2 is one of these demos)]
194: - Changes in bitplane data during one line. If programs do this kind of
195: thing, it's most likely accidental and the program is broken. Can happen
196: with programs that use the blitter incorrectly, like all the Andromeda
197: demos.
198: - others? (fill in if you can think of anything)
199:
200: All in all, it's unlikely that this causes compatibility problems. If it does,
201: fudge values could be introduced (although that sort of thing gets messy
202: quickly).
1.1 root 203:
204:
1.1.1.3 root 205: * Native code vs. 68k code
1.1.1.2 root 206:
1.1.1.3 root 207: It is possible to call native code from 68k code; autoconf.c has some routines
208: which make setting up a call trap very easy. However, it is not as easy to
209: call 68k code from native C code, at least not while Amiga Exec multitasking
210: is running. You ask why?
211:
212: Amiga process1 calls native function foo
213: Native function foo calls some 68k function and goes into 68k mode
214: Amiga context switch happens, process1 is put to sleep and process2 gets run.
215: Amiga process2 calls native function foo
216: Native function foo calls some 68k function and goes into 68k mode
217: Amiga context switch happens, process2 is put to sleep and process1 gets run.
218: Process 1 completes the 68k function called by foo and returns from 68k mode.
219:
220: There. Now we are in function foo again. When it called the 68k code, process2
221: was active. Now process1 is active, and the function we called in process2
222: hasn't completed yet. What a mess.
223:
224: To get around this, you need to do some stack magic. Code to do this exists,
225: but it must be adapted for each port, since setting up a different stack is
226: completely non-portable.
227:
228:
229: * How multithreading in filesys.c works
230:
231: AmigaOS is nice enough to start one processes for each mounted filesystem. All
232: of these run in the 68k emulation code, i.e. in the main UAE thread. This is
233: the reason why multithreading is desirable: if the main UAE thread blocks
234: waiting for I/O, the CPU emulation can't continue to run. Since the Amiga OS
235: is capable of multi-tasking, it is possible that other code could run until
236: the I/O operation is complete. The most important bit of code that can run is
237: the code that moves the mouse pointer - it's unpleasant if the pointer does
238: not follow mouse movement during disk/CD accesses.
239:
240: When a packet is received by the filesys.asm code, filesys_handler is called.
241: This function always runs in the main UAE thread.
242: - In the single-threaded case, this function performs the action that was
243: requested, then returns 0 to indicate "action completed, reply packet".
244: Nothing else is performed.
245: - In the multi-threaded case, filesys_handler figures out which unit the
246: packet was for and sends the packet to the UAE thread responsible for
247: handling this unit. filesys_handler returns 0 to indicate: queue the
248: packet. Also, one (at that point unused) field in the packet is set to
249: 0 to indicate that the action was not completed.
250:
251: The latter case is the interesting one. The thread that got the packet does
252: the following:
253: - perform the action as usual
254: - set the "command complete" field in the packet to -1.
255: - send a message to the AmigaOS (!) filesystem process. However, it can't do
256: that without some effort. We can't call 68k code from the emulator easily.
257: So we have to use an Amiga interrupt. The filesystem init code sets up an
258: Exec IntServer for the EXTER interrupt, and hsync_handler() checks
259: periodically whether the filesystem needs an interrupt and raises one if
260: necessary.
261: Only one dummy message is used per filesystem unit, which is allocated at
262: startup. This means that there must be some locking to prevent the unit
263: thread from sending the same message twice to the same port. To determine
264: whether the message is free, three counts are kept. "cmds_sent" is
265: incremented by the UAE thread whenever it has completed a command.
266: "cmds_acked" is set to the same value of cmds_sent at the point that the
267: interrupt handler got invoked and decided it must send a message. Finally,
268: cmds_complete is set to this value at the time the AmigaOS process receives
269: the dummy message. Whenever cmds_acked == cmds_complete, the dummy message
270: is free to be sent again.
271:
272: The EXTER interrupt basically walks through the units, looks at the cmds_*
273: fields and sends the dummy message to the Amiga filesystem process when
274: possible and necessary.
275:
276: When the Amiga filesystem process receives such a dummy message, it does the
277: following:
278: - increment cmds_complete as described above.
279: - walk through the queue of unprocessed commands and see which ones now have
280: a status of -1, indicating that they are finished. These are removed from
281: the queue and replied to.
282:
283:
284: * Calltraps at fixed locations
285:
286: F0FF00: return from 68k mode.
287: F0FF10: must have gotten lost somewhere ;)
288: F0FF20: used by filesys.c to store away some information from the startup
289: packet.
290: F0FF30: filesys_handler().
291: F0FF40: startup_handler(), handles only the startup packet for each
292: filesystem.
293: F0FF50: used by the EXTER interrupt which we set up for the filesystem.
294: F0FF60: used by the uaectrl/uae-control programs (see uaelib.c)
295: F0FF70: used by the task that gets set up for the mouse emulation.
1.1.1.2 root 296:
1.1.1.5 root 297:
1.1.1.3 root 298: * How the compiler works
1.1.1.2 root 299:
300: .. yet to be written. To be decided, in fact.
1.1.1.3 root 301:
302:
303: Portability
304:
305: This section was out of date. I'll rewrite it.
306: Some day.
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