source: buchla-68k/orig/DOC/MTASK.TXT

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1Mutli-Tasker Notes -- 1988-04-14 -- Rev 15 D.N. Lynx Crowe
2
3Summary
4-------
5
6. Task scheduling:
7
8 . Priority scheduler
9
10 . Multiple priority levels, 0..65535 (0 is lowest)
11
12 . Round-Robin scheduling within each level
13
14 . Multi-level interrupt support
15
16 . Time slicing optionally supported
17
18 . Tasks are either stopped, waiting, ready, or running
19
20 . Arbitrary number of Task Control Blocks (up to 65535)
21
22 . Swapping rules designed to minimize chance of system lockup
23
24
25
26. Inter-task communication:
27
28 . Supports counting semaphores for event signalling or
29 control of exclusive access to shared resources
30
31 . Supports inter-task mailboxes (message queues)
32
33
34Multitasker support functions
35-----------------------------
36
37 . Task functions
38
39 void MTInit()
40 unsigned MTID()
41 short MTRun(tid, pri, stat, slice, pstack, func, par)
42 void MTSetT(tcp, tid, pri, stat, slice, pstack, func, par)
43 unsigned MTSetP(pri)
44 void MTSwap()
45 void MTNext()
46 short MTStop(tid)
47 short MTZap(tid)
48 void MTExit()
49 void MTQuit()
50 short MTStat(tid)
51 unsigned MTGetID()
52
53
54 . Semaphore functions
55
56 void SMInit(psem, n)
57 short SMStat(psem)
58 void SMSig(psem)
59 void SMWait(psem)
60 short SMCSig(psem)
61 short SMCWait(psem)
62
63
64 . Mailbox functions
65
66 void MBInit(pmbox)
67 void MBSend(pmbox, pmsg)
68 MSG * MBRecv(pmbox)
69 MSG * MBChek(pmbox)
70 short MBDel(pmbox, pmsg)
71
72
73 . System variables
74
75 TCB *MT_TCBs pointer to TCB chain
76 TCB *MT_CurP pointer to current TCB
77 TCB *MT_RdyQ pointer to ready queue
78 unsigned MT_IDct task ID assignment counter
79 unsigned *_MT_Vc1 saved TRAP 8 vector (_MT_Swp)
80 unsigned *_MT_Vc2 saved TRAP 9 vector (_MT_Nxt)
81 long _MT_Stk[48] stack for _MT_Nil() (null task)
82 TCB _MT_TCB dummy TCB for shutdown
83
84
85Data structures
86---------------
87
88 . SEM - Semaphore (counting type)
89
90 typedef long SEM;
91
92 . Single 32 bit word per semaphore used for both semaphore
93 counter and wait queue pointer
94
95 . LSB indicates status of semaphore and meaning of MS bits
96
97 . 1 = MS bits are the number of signals received and
98 not processed
99
100 . 0 = MS bits are a pointer to the queue of tasks
101 waiting on the semaphore
102
103 . Initialize to a count of 0 (value = 0) for event
104 signalling, or to a count of 1 (value = 3) for
105 controlling mutually exclusive access to a shared
106 resource
107
108
109 . MSG - Message
110
111 typedef struct MSG {
112
113 MSG *next;
114 SEM reply; /* initialize to 0 */
115 long msize;
116 long mdata;
117 };
118
119 . Consists of a queue pointer, a semaphore, a size variable,
120 and a data pointer
121
122 . 'next' -- pointer -- points to the next message
123 in the message queue
124
125 . 'reply' -- semaphore -- used to indicate reply status
126
127 . 'msize' -- variable -- contains the size of the
128 message if 'mdata' contains a pointer, or 0 if 'mdata'
129 contains the data itself
130
131 . 'mdata' -- variable -- points to the actual data,
132 or is the data itself
133
134
135 . MBOX - Mailbox (intertask message queue)
136
137 typedef struct MBOX {
138
139 SEM mail; /* initialize to zero */
140 SEM mutex; /* initialize to 1 */
141 MSG *head; /* initialize to NIL */
142 MSG *tail; /* initialize to NIL */
143 };
144
145 . Managed by two semaphores and two pointers
146
147 . 'mail' -- semaphore -- indicates messages present
148 in the message queue
149
150 . 'mutex' -- semaphore -- enforces mutually exclusive
151 access to the message queue
152
153 . 'head' -- pointer -- points to the first message
154 in the message queue, or NIL if the queue is empty
155
156 . 'tail' -- pointer -- points to the last message
157 in the message queue, or NIL if the queue is empty
158
159
160 . TCB - Task Control Block
161
162 typedef struct TCB {
163
164 TCB *next; 4 bytes
165 TCB *fwd; 4 bytes
166 unsigned tid; 2 bytes
167 unsigned pri; 2 bytes
168 long slice; 4 bytes
169 long reg[16]; 64 bytes
170 long sp; 4 bytes
171 long pc; 4 bytes
172 unsigned sr; 2 bytes
173 unsigned flags; 2 bytes
174 long tos; 4 bytes
175 }; --
176 96 bytes total
177
178 . 'next' points to the next task in the task queue or NIL
179
180 . 'fwd' points to the next TCB in the TCB chain
181
182 . 'tid' contains the task identifier (0..65536)
183
184 . 'pri' contains the task priority (0..65535, 0 is lowest)
185
186 . 'slice' contains the time slice (milliseconds) for the task,
187 or -1 for a task that isn't sliced
188
189 . 'reg[]' contains the task register contents when
190 the task is not executing (D0-D7/A0-A7)
191
192 . 'sp' contains the task stack pointer when the task
193 is not executing
194
195 . 'pc' contains the task Program Counter contents when
196 the task is not executing
197
198 . 'sr' contains the task Status Register contents when
199 the task is not executing
200
201 . 'flags' contains the task control flags:
202
203 MTF_OCC 0x8000 /* TCB occupied */
204 MTF_RDY 0x0001 /* task ready to run (on MT_RdyQ) */
205 MTF_SWT 0x0002 /* task waiting on a semaphore */
206 MTF_RUN 0x0004 /* task running (MT_CurP) */
207 MTF_STP 0x0008 /* task to be stopped (waiting) */
208
209 . 'tos' points to the top of the task's stack
210
211
212Multitasker support function calling sequences
213----------------------------------------------
214
215 . Initialize the multi-tasker
216
217 void
218 MTInit()
219
220 . Get next available task ID
221
222 unsigned task ID
223 MTID()
224
225 . Acquire and initialize a TCB and start a task
226
227 short result code
228 MTRun(tid, pri, stat, slice, pstack, func, par)
229 unsigned tid; task ID
230 unsigned pri; initial task priority
231 unsigned stat; initial task status register
232 long slice; time slice, or -1
233 long pstack; top of stack address
234 short (*func)(); initial task program counter
235 long par; long parameter passed to task
236
237 result code:
238
239 SUCCESS TCB created and placed on ready queue
240 FAILURE no TCB available for task
241
242 Note: acquires a free TCB from the current chain of known TCBs.
243
244 . Initialize a specific TCB and start a task
245
246 MTSetT(tcp, tid, pri, stat, slice, pstack, func, par)
247 TCB *tcp; TCB pointer
248 unsigned tid; task ID
249 unsigned pri; initial task priority
250 unsigned stat; initial task status register
251 long slice; time slice, or -1
252 long pstack; top of stack address
253 short (*func)(); initial task program counter
254 long par; long parameter passed to task
255
256 Note: adds the TCB to the current chain of known TCBs.
257
258
259 . Set the priority of the current task and swap to the highest
260 priority ready task
261
262 unsigned old priority (0..65535)
263 MTSetP(pri)
264 unsigned pri; new priority (0..65535)
265
266 . Swap to the highest priority ready task,
267 re-schedule the current task
268
269 void
270 MTSwap();
271
272 . Swap to the highest priority ready task,
273 don't re-schedule the current task
274
275 void
276 MTNext();
277
278 Note: this is an internal function, use with caution.
279
280 . Stop a specific task
281
282 short result code
283 MTStop(tid)
284 unsigned tid; task ID of task to stop
285
286 result code:
287
288 -3 - task not stopped (was the current task)
289 -2 - task not stopped (can't find it on ready queue)
290 -1 - task not stopped (can't find it at all)
291 0 - task stopped (was ready to run)
292 1 - task stopped (was waiting)
293 2 - task already stopped (wasn't waiting or on ready queue)
294 3 - task will be stopped (has MTF_STP set)
295
296 . Delete a specific task, free its TCB
297
298 short result code
299 MTZap(tid)
300 unsigned tid; task ID
301
302 result code:
303
304 -1 not deleted (was active or waiting)
305 0 deleted
306 1 not found
307
308
309 . Terminate the current task, free its TCB
310
311 void
312 MTExit()
313
314 . Shut down the multi-tasker
315
316 void
317 MTQuit();
318
319 Note: this brings everything to a halt. Use with caution.
320
321 . Get the task ID of the currently running task
322
323 unsigned
324 MTGetID()
325
326 . Check the state of a specific task
327
328 short result code
329 MTStat(tid)
330 unsigned tid; task ID
331
332 result code:
333
334 -3 stopped, waiting on a sempahore
335 -2 stopped, not waiting
336 -1 not found
337 0 running (current task)
338 1 ready to run
339 2 waiting on a sempahore
340
341
342
343Semaphore Operation function calling sequences
344----------------------------------------------
345
346 . Initialize a semaphore
347
348 void
349 SMInit(psem, n)
350 SEM *psem; pointer to semaphore
351 long n; count to put in semaphore
352
353 . Check the status of a semaphore
354
355 short result code
356 SMStat(psem)
357 SEM *psem; pointer to semaphore
358
359 result code:
360
361 -1 awaited at least one process is waiting
362 0 not signalled no signals, no waiting processes
363 1 signalled at least one unreceived signal
364
365 . Signal a semphore
366
367 void
368 SMSig(psem)
369 SEM *psem; pointer to semaphore
370
371 . Wait on a semaphore
372
373 void
374 SMWait(psem)
375 SEM *psem; pointer to semaphore
376
377
378 . Conditionally signal a semaphore
379
380 short result code
381 SMCSig(psem)
382 SEM *psem; pointer to semaphore
383
384 result code:
385
386 -1 stopped task signalled
387 0 nothing signalled
388 1 waiting task signalled
389
390 . Conditional wait on a semaphore
391
392 short result code
393 SMCWait(psem)
394 SEM *psem; pointer to semaphore
395
396 result code:
397
398 TRUE semaphore was non-zero, and was decremented
399 FALSE semaphore was zero, or tasks were waiting for it
400
401
402Mailbox Operation function calling sequences
403--------------------------------------------
404
405 . Initialize a mailbox
406
407 void
408 MBInit(pmbox)
409 MBOX *pmbox; pointer to mailbox
410
411 . Send a message to a mailbox queue
412
413 void
414 MBSend(pmbox, pmsg)
415 MBOX *pmbox; pointer to mailbox
416 MSG *pmsg; pointer to message
417
418 . Receive a message from a mailbox queue (wait for message)
419
420 MSG * pointer to message received
421 MBRecv(pmbox)
422 MBOX *pmbox; pointer to mailbox
423
424 . Check for a message from a mailbox queue and conditionally receive it
425
426 MSG * pointer to message, or NIL
427 MBChek(pmbox)
428 MBOX *pmbox; pointer to mailbox
429
430 . Delete a message from a mailbox queue (cancel message)
431
432 short result code
433 MBDel(pmbox, pmsg)
434 MBOX *pmbox; pointer to mailbox
435 MSG *pmsg; pointer to message
436
437 result code:
438
439 FAILURE unable to find the message
440 SUCCESS message found and deleted from mailbox
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