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--- en:pfw:multi_tasker [2024-08-17 09:57] – [Implementation specific and example] willem
+++ en:pfw:multi_tasker [2025-02-27 21:13] (current) – [Contributions] willem
@@ Line 1: / Line 1: @@
 ===== Cooperative multitasker =====
-<html><h2 style="background-color:yellow">Under construction</h2></html>
@@ Line 15: / Line 14: @@
   * **You determine the task change with** ''%%PAUSE%%''
   * **The basic word set:** ''%%TASK%%'' ''%%TASK:%%'' ''%%START-TASK%%'' ''%%WAKE%%'' ''%%SLEEP%%'' ''%%STOP%%'' ''%%PAUSE%%''
+{{ :pfw:multitasker_memory_use.gif?direct&400 |}}
 A picture of three installed tasks, task3 is asleep.\\
+All the tasks link to each other so they form a circular list.\\
 Note that the number of task variables may vary for an other implementation.\\
 The clue is to find out what's the most efficient method is for a given CPU & Forth implementation.\\
-^  TCB  ^  Task1  ^  Task2  ^  Task3  ^
+^  TCB  ^  Task1  ^  Task2  ^  Task3  ^  Function  ^
-|  **Link**  |  task2  |  task3  |  task1  |
+|  **Link**  |  task2  |  task3  |  task1  | Tasks link chain |
-|  **Tstate**  |  true  |  true  |  false  |
+|  **Tstate**  |  true  |  true  |  false  | Active flag, true = active |
-|  **Error#**  |  0  |  0  |  0  |
+|  **Error#**  |  0  |  0  |  0  | Error number, 0 = no error |
-|  **TRP**  |  ptr1  |  ptr2  |  ptr3  |
+|  **TRP**  |  ptr1  |  ptr2  |  ptr3  | Return stack pointer |
-|  **TR0**  |  ptr1  |  ptr2  |  ptr3  |
+|  **TR0**  |  adr1  |  adr2  |  adr3  | Return stack bottom |
-|  **TS0**  |  ptr1  |  ptr2  |  ptr3  |
+|  **TS0**  |  adr1  |  adr2  |  adr3  | Data stack bottom |
 <html>
@@ Line 194: / Line 196: @@
 ==== Implementation specific and example ====
-This part is system specific (noForth t) and it's just an sample implementation:\\
+This part is system specific (noForth t) and it's just a sample implementation:\\
 <code forth>
 \ Redefine teminal I/O and MS to include multitasker
@@ Line 232: / Line 234: @@
 <# # # # # # # # # #> type space ;
-: TASKS     ( -- )  \ Show all data from the TCB
+: TASKS     ( -- )  \ Show all eight data cells from the TCB
     main
     begin
@@ Line 248: / Line 250: @@
     swap >r  false r@ terr? his !   \ Reset tasks error flag
     swap r@ >task  r> wake ;        \ Set task ready and start it
+</code>
+==== Semaphores ====
+Semaphores are a way to make part of the processor (temporary) your own.
+When several tasks need the same device it is not very handy that they
+access this device at about the same time. That's where semaphores can be used.
+<code forth>
+: LOCK      ( sema -- )
+    dup @ TP = IF  drop exit  THEN  \ Do nothing when i own it
+    BEGIN  dup @ WHILE pause REPEAT \ Semaphore not mine, to next task
+    TP swap ! ;                     \ Semaphore free, grab it!
+: UNLOCK    ( sema -- )     dup lock  false swap ! ; \ Free semaphore
 </code>
@@ Line 254: / Line 271: @@
 <html><h2 style="background-color:yellow">Implementations</h2></html>
+**Primitives for noForth t on the RP2040**
+Note that this is code directly from the noForth t metacompiler listing.\\
+So take there there are some meta specific words in it like ''>box'', ''box>'' & ''tp>''.\\
+<code forth>
+code PAUSE      ( -- ) \ 29 machine cycles, is 0.232 microsec. at 125 MHz
+    { ip sp tos } push,     \ 4 - Save Forth environment
+    sun TP mov,             \ 1 - TCB address to SUN
+    day rp mov,             \ 1 - RP to DAY
+    day  sun 0C #) str,     \ 2 - DAY to RP
+    begin, >box
+    begin,                  \ An inactive task takes 7 cycles extra = 0.056 µs
+        sun  sun ) ldr,     \ 2 - Fetch next link to SUN
+        day  sun 4 #) ldr,  \ 2 - Next TSTATE @ to DAY
+        day 0 # cmp,        \ 1 -
+    =? no until,            \ 2 - Not zero?
+    TP sun mov,             \ 1 - Next link address = new TCB
+    day  sun 0C #) ldr,     \ 2 - RP @ to DAY
+    rp day mov,             \ 1 - DAY to RP
+    { ip sp tos } pop,      \ 4 - Restore Forth environment
+    begin, >box
+    next,                   \ 6
+end-code
+code STOP   ( -- )
+    tp> ,  ( Address of main TCB )
+code>
+    w  w ) ldr,             \ 2 - main to W
+    sun TP mov,             \ 1 - Task to DAY
+    sun w cmp,              \ 1 - main = task?
+    box> =? no until,       \ 2 - No = continue, yes = ready
+    day 0 # movs,           \ 1 - False flag
+    day  sun 4 #) str,      \ 2 - Store in TSTATE of myself
+    { ip sp tos } push,     \ 4 - Save this tasks Forth environment
+    w rp mov,               \ 1 - RP to W
+    w  sun 0C #) str,       \ 2 - W to RP
+  box> again,               \ 2 - Switch to next task
+end-code
+code SLEEP  ( task -- )
+    tp> ,  ( Address of main TCB )
+code>
+    w  w ) ldr,             \ 2 - main to W
+    tos w cmp,              \ 1 - main = task?
+    =? no if, >box          \ 2 - No = continue, yes = ready
+    day 0 # movs,           \ 1
+  ahead, >box               \ 10 + 2
+end-code
+code WAKE   ( task -- )
+    day 0 # movs,           \ 1 - Build true flag
+    day day mvns,           \ 1
+    box> then,              \     Resolve jump
+    day  tos 4 #) str,      \ 2 - Store in TSTATE of task
+    box> then,
+    tos sp )+ ldr,          \ 2 - Drop task
+    next,                   \ 6
+end-code
+code >TASK ( ip xt task -- )
+    sp  { hop sun } ldm,    \ XT to HOP, IP to SUN
+    { ip sp } push,         \ Save noForth registers
+    moon rp mov,            \ Save RP
+    ip sun mov,             \ Ip to IP
+    day tos 20 #) ldr,      \ Read R0 to DAY
+    rp day mov,             \ Use R0 as tasks RP
+    sp tos 24 #) ldr,       \ Set SP to S0
+    { ip sp tos hop } push, \ Initialise tasks return stack
+    day rp mov,             \ Copy RP to DAY
+    day  tos 0C #) str,     \ Set tasks RP too
+    rp moon mov,            \ Restore noForth registers
+    { ip sp } pop,
+    tos  sp )+ ldr,         \ Pop stack
+    next,
+end-code
+</code>