paul@0 | 1 | ; A task switcher for the Acorn Electron. |
paul@0 | 2 | |
paul@0 | 3 | ; Copyright (C) 2015 Paul Boddie <paul@boddie.org.uk> |
paul@0 | 4 | |
paul@0 | 5 | ; This program is free software; you can redistribute it and/or modify it under |
paul@0 | 6 | ; the terms of the GNU General Public License as published by the Free Software |
paul@0 | 7 | ; Foundation; either version 3 of the License, or (at your option) any later |
paul@0 | 8 | ; version. |
paul@0 | 9 | |
paul@0 | 10 | ; This program is distributed in the hope that it will be useful, but WITHOUT |
paul@0 | 11 | ; ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS |
paul@0 | 12 | ; FOR A PARTICULAR PURPOSE. See the GNU General Public License for more |
paul@0 | 13 | ; details. |
paul@0 | 14 | |
paul@0 | 15 | ; You should have received a copy of the GNU General Public License along with |
paul@0 | 16 | ; this program. If not, see <http://www.gnu.org/licenses/>. |
paul@0 | 17 | |
paul@0 | 18 | .include "macros.oph" |
paul@0 | 19 | |
paul@3 | 20 | .alias IRQ1V $204 |
paul@3 | 21 | |
paul@2 | 22 | .alias SP $70 |
paul@2 | 23 | .alias SPH $71 |
paul@2 | 24 | .alias NEXT $72 |
paul@2 | 25 | .alias NEXTH $73 |
paul@2 | 26 | .alias CURRENT $74 |
paul@2 | 27 | .alias CURRENTH $75 |
paul@5 | 28 | .alias USER $76 |
paul@5 | 29 | .alias ARG0 $80 |
paul@5 | 30 | .alias ARG0H $81 |
paul@5 | 31 | .alias ARG1 $82 |
paul@5 | 32 | .alias ARG1H $83 |
paul@2 | 33 | |
paul@3 | 34 | .alias TASK_TABLE_LENGTH 10 |
paul@3 | 35 | |
paul@5 | 36 | ; "user space" stack for the main program where the invocations might be |
paul@5 | 37 | ; interrupted and where the CPU stack might be disrupted |
paul@5 | 38 | |
paul@5 | 39 | .alias main_stack $1fff |
paul@5 | 40 | |
paul@5 | 41 | |
paul@5 | 42 | |
paul@0 | 43 | .org $2000 |
paul@0 | 44 | .text |
paul@5 | 45 | |
paul@5 | 46 | |
paul@5 | 47 | |
paul@5 | 48 | ; main program, installing the handler and adding example tasks |
paul@5 | 49 | |
paul@0 | 50 | main: |
paul@0 | 51 | jsr install_handler |
paul@5 | 52 | .invoke store16 tasks, ARG1 |
paul@5 | 53 | .invoke store16 main_stack, USER |
paul@5 | 54 | .invoke store16 first_task, ARG0 |
paul@5 | 55 | .invoke call new_task |
paul@5 | 56 | .invoke store16 second_task, ARG0 |
paul@5 | 57 | .invoke call new_task |
paul@5 | 58 | .invoke store16 third_task, ARG0 |
paul@5 | 59 | .invoke call new_task |
paul@4 | 60 | wait: |
paul@4 | 61 | jmp wait ; wait for the switcher to take over |
paul@0 | 62 | |
paul@3 | 63 | |
paul@3 | 64 | |
paul@5 | 65 | ; move CPU stack data to the "user space" stack |
paul@5 | 66 | ; |
paul@5 | 67 | ; affects: USER (gains LSB, MSB) |
paul@5 | 68 | |
paul@5 | 69 | copy_to_user_stack: |
paul@5 | 70 | pha ; A -> stack |
paul@5 | 71 | txa |
paul@5 | 72 | pha ; X -> stack |
paul@5 | 73 | tsx ; capture the stack pointer now for later use |
paul@5 | 74 | ; (stack is Y, X, A, LSB, MSB) |
paul@5 | 75 | tya |
paul@5 | 76 | pha ; Y -> stack |
paul@5 | 77 | |
paul@5 | 78 | ; save zero-page locations used |
paul@5 | 79 | |
paul@5 | 80 | .invoke push16 SP |
paul@5 | 81 | |
paul@5 | 82 | ; initialise the stack frame pointer |
paul@5 | 83 | |
paul@5 | 84 | txa |
paul@5 | 85 | sta SP |
paul@5 | 86 | lda #$01 ; $01xx |
paul@5 | 87 | sta SPH |
paul@5 | 88 | |
paul@5 | 89 | ; allocate "user space" stack space to be compatible with the CPU stack |
paul@5 | 90 | |
paul@5 | 91 | .invoke sub16 5, USER |
paul@5 | 92 | |
paul@5 | 93 | ; copy the PC, updated by 4 (see the call macro) |
paul@5 | 94 | |
paul@5 | 95 | ldy #3 |
paul@5 | 96 | clc |
paul@5 | 97 | lda (SP), y |
paul@5 | 98 | adc #4 |
paul@5 | 99 | sta (USER), y |
paul@5 | 100 | iny |
paul@5 | 101 | lda (SP), y |
paul@5 | 102 | adc #0 |
paul@5 | 103 | sta (USER), y |
paul@5 | 104 | |
paul@5 | 105 | ; correct "user space" stack |
paul@5 | 106 | |
paul@5 | 107 | .invoke add16 3, USER |
paul@5 | 108 | |
paul@5 | 109 | ; restore zero-page locations used |
paul@5 | 110 | |
paul@5 | 111 | .invoke pull16 SP |
paul@5 | 112 | |
paul@5 | 113 | ; return to the caller |
paul@5 | 114 | |
paul@5 | 115 | pla |
paul@5 | 116 | tay ; stack -> Y |
paul@5 | 117 | pla |
paul@5 | 118 | tax ; stack -> X |
paul@5 | 119 | pla ; stack -> A |
paul@5 | 120 | rts |
paul@5 | 121 | |
paul@5 | 122 | |
paul@5 | 123 | |
paul@5 | 124 | ; move CPU stack data from the "user space" stack |
paul@5 | 125 | ; |
paul@5 | 126 | ; affects: USER (loses LSB, MSB) |
paul@5 | 127 | |
paul@5 | 128 | copy_from_user_stack: |
paul@5 | 129 | pha ; padding |
paul@5 | 130 | pha ; padding |
paul@5 | 131 | pha ; A -> stack |
paul@5 | 132 | txa |
paul@5 | 133 | pha ; X -> stack |
paul@5 | 134 | tsx ; capture the stack pointer now for later use |
paul@5 | 135 | ; (stack is Y, X, A, LSB, MSB) |
paul@5 | 136 | tya |
paul@5 | 137 | pha ; Y -> stack |
paul@5 | 138 | |
paul@5 | 139 | ; save zero-page locations used |
paul@5 | 140 | |
paul@5 | 141 | .invoke push16 SP |
paul@5 | 142 | |
paul@5 | 143 | ; initialise the stack frame pointer |
paul@5 | 144 | |
paul@5 | 145 | txa |
paul@5 | 146 | sta SP |
paul@5 | 147 | lda #$01 ; $01xx |
paul@5 | 148 | sta SPH |
paul@5 | 149 | |
paul@5 | 150 | ; adjust the "user space" stack pointer to be compatible with the PC stack |
paul@5 | 151 | |
paul@5 | 152 | .invoke sub16 3, USER |
paul@5 | 153 | |
paul@5 | 154 | ; copy the PC |
paul@5 | 155 | |
paul@5 | 156 | ldy #3 |
paul@5 | 157 | .invoke mov8_refs USER, SP |
paul@5 | 158 | iny |
paul@5 | 159 | .invoke mov8_refs USER, SP |
paul@5 | 160 | |
paul@5 | 161 | ; update the "user space" stack pointer |
paul@5 | 162 | |
paul@5 | 163 | .invoke add16 5, USER |
paul@5 | 164 | |
paul@5 | 165 | ; restore zero-page locations used |
paul@5 | 166 | |
paul@5 | 167 | .invoke pull16 SP |
paul@5 | 168 | |
paul@5 | 169 | ; return to the stored PC |
paul@5 | 170 | |
paul@5 | 171 | pla |
paul@5 | 172 | tay ; stack -> Y |
paul@5 | 173 | pla |
paul@5 | 174 | tax ; stack -> X |
paul@5 | 175 | pla ; stack -> A |
paul@5 | 176 | rts |
paul@5 | 177 | |
paul@5 | 178 | |
paul@5 | 179 | |
paul@0 | 180 | ; install the interrupt handler address in IRQ1V |
paul@0 | 181 | ; |
paul@0 | 182 | ; affects: A |
paul@0 | 183 | |
paul@0 | 184 | install_handler: |
paul@0 | 185 | sei |
paul@3 | 186 | .invoke mov16 IRQ1V, old_handler |
paul@3 | 187 | .invoke store16 handler, IRQ1V |
paul@0 | 188 | cli |
paul@0 | 189 | rts |
paul@0 | 190 | |
paul@3 | 191 | |
paul@3 | 192 | |
paul@0 | 193 | ; handle interrupts |
paul@0 | 194 | ; |
paul@0 | 195 | ; affects: (temporary stack usage) |
paul@0 | 196 | |
paul@0 | 197 | handler: |
paul@0 | 198 | pha ; A -> stack |
paul@0 | 199 | txa |
paul@0 | 200 | pha ; X -> stack |
paul@2 | 201 | tsx ; capture the stack pointer now for later use |
paul@2 | 202 | ; (stack is <empty>, X, A, F, LSB, MSB) |
paul@0 | 203 | tya |
paul@0 | 204 | pha ; Y -> stack |
paul@2 | 205 | |
paul@2 | 206 | ; save zero-page locations used in the handler |
paul@2 | 207 | |
paul@2 | 208 | .invoke push16 SP |
paul@2 | 209 | .invoke push16 NEXT |
paul@2 | 210 | .invoke push16 CURRENT |
paul@2 | 211 | |
paul@2 | 212 | init_sp: |
paul@2 | 213 | |
paul@2 | 214 | ; initialise the stack frame pointer |
paul@2 | 215 | |
paul@2 | 216 | txa |
paul@2 | 217 | sta SP |
paul@2 | 218 | lda #$01 ; $01xx |
paul@2 | 219 | sta SPH |
paul@2 | 220 | |
paul@2 | 221 | test_pc: |
paul@0 | 222 | |
paul@0 | 223 | ; test PC for execution of ROM routines |
paul@0 | 224 | ; these are probably not re-entrant |
paul@0 | 225 | |
paul@0 | 226 | ; obtain the stack location of the stored PC MSB |
paul@0 | 227 | |
paul@2 | 228 | ldy #5 ; offset of MSB (Y, X, A, F, LSB, MSB) |
paul@2 | 229 | lda (SP), y |
paul@0 | 230 | |
paul@0 | 231 | ; reference the stack location and compute PC MSB & $80 |
paul@0 | 232 | and #$80 |
paul@0 | 233 | cmp #$80 |
paul@0 | 234 | |
paul@0 | 235 | ; exit if PC MSB & $80 != 0 |
paul@0 | 236 | beq exit_handler |
paul@0 | 237 | |
paul@2 | 238 | load_task: |
paul@2 | 239 | |
paul@2 | 240 | ; load next task |
paul@2 | 241 | |
paul@3 | 242 | ldx task_offset |
paul@2 | 243 | lda tasks, x |
paul@2 | 244 | sta NEXT |
paul@2 | 245 | inx |
paul@2 | 246 | lda tasks, x |
paul@2 | 247 | sta NEXTH |
paul@2 | 248 | inx |
paul@2 | 249 | |
paul@2 | 250 | ; reset the task index if necessary |
paul@2 | 251 | |
paul@3 | 252 | cpx #TASK_TABLE_LENGTH |
paul@2 | 253 | bne test_task |
paul@2 | 254 | ldx #0 |
paul@2 | 255 | |
paul@2 | 256 | test_task: |
paul@3 | 257 | stx task_offset |
paul@2 | 258 | |
paul@2 | 259 | ; exit if null task |
paul@2 | 260 | |
paul@2 | 261 | lda NEXTH |
paul@2 | 262 | cmp #0 |
paul@2 | 263 | beq exit_handler |
paul@2 | 264 | |
paul@2 | 265 | switch_task: |
paul@2 | 266 | |
paul@2 | 267 | ; store flags, PC in current task structure |
paul@2 | 268 | |
paul@2 | 269 | .invoke mov16 current_task, CURRENT |
paul@2 | 270 | |
paul@5 | 271 | ; store the user stack for the task |
paul@5 | 272 | |
paul@5 | 273 | .invoke mov16_to_ref USER, CURRENT |
paul@5 | 274 | |
paul@2 | 275 | ldy #5 ; offset of MSB (Y, X, A, F, LSB, MSB) |
paul@5 | 276 | .invoke mov8_refs SP, CURRENT |
paul@2 | 277 | dey |
paul@5 | 278 | .invoke mov8_refs SP, CURRENT |
paul@2 | 279 | dey |
paul@5 | 280 | .invoke mov8_refs SP, CURRENT |
paul@2 | 281 | |
paul@2 | 282 | ; load flags, PC from next task structure |
paul@2 | 283 | |
paul@5 | 284 | .invoke mov8_refs NEXT, SP |
paul@2 | 285 | iny |
paul@5 | 286 | .invoke mov8_refs NEXT, SP |
paul@2 | 287 | iny |
paul@5 | 288 | .invoke mov8_refs NEXT, SP |
paul@2 | 289 | iny |
paul@2 | 290 | |
paul@2 | 291 | ; make the next task the current one |
paul@2 | 292 | |
paul@2 | 293 | .invoke mov16 NEXT, current_task |
paul@0 | 294 | |
paul@5 | 295 | ; set the user stack for the task |
paul@5 | 296 | |
paul@5 | 297 | .invoke mov16_from_ref NEXT, USER |
paul@5 | 298 | |
paul@0 | 299 | exit_handler: |
paul@2 | 300 | |
paul@2 | 301 | ; restore zero-page locations used in the handler |
paul@2 | 302 | |
paul@2 | 303 | .invoke pull16 CURRENT |
paul@2 | 304 | .invoke pull16 NEXT |
paul@2 | 305 | .invoke pull16 SP |
paul@2 | 306 | |
paul@0 | 307 | pla |
paul@0 | 308 | tay ; stack -> Y |
paul@0 | 309 | pla |
paul@0 | 310 | tax ; stack -> X |
paul@0 | 311 | pla ; stack -> A |
paul@0 | 312 | jmp (old_handler) |
paul@0 | 313 | |
paul@3 | 314 | |
paul@3 | 315 | |
paul@2 | 316 | ; location of previous interrupt handler |
paul@2 | 317 | |
paul@0 | 318 | old_handler: .word 0 |
paul@0 | 319 | |
paul@2 | 320 | ; location of current task (duplicated from the table) |
paul@2 | 321 | |
paul@2 | 322 | current_task: .word 0 |
paul@2 | 323 | |
paul@3 | 324 | ; offset of current task in table (in multiples of 2) |
paul@2 | 325 | |
paul@3 | 326 | task_offset: .byte 0 |
paul@2 | 327 | |
paul@2 | 328 | ; task table containing locations of each task |
paul@2 | 329 | |
paul@2 | 330 | tasks: |
paul@3 | 331 | .word 0 |
paul@3 | 332 | .word 0 |
paul@2 | 333 | .word 0 |
paul@2 | 334 | .word 0 |
paul@2 | 335 | .word 0 |
paul@2 | 336 | |
paul@3 | 337 | |
paul@3 | 338 | |
paul@3 | 339 | ; add a new task to the table |
paul@3 | 340 | ; |
paul@5 | 341 | ; ARG0, ARG0H: location of task structure |
paul@3 | 342 | ; affects: A, Y |
paul@3 | 343 | |
paul@3 | 344 | new_task: |
paul@3 | 345 | |
paul@3 | 346 | ; check the MSB of each task table entry |
paul@3 | 347 | |
paul@3 | 348 | ldy #1 |
paul@4 | 349 | |
paul@4 | 350 | check_new_task: |
paul@3 | 351 | lda tasks, y |
paul@3 | 352 | cmp #0 |
paul@3 | 353 | beq add_new_task |
paul@3 | 354 | iny |
paul@3 | 355 | iny |
paul@3 | 356 | |
paul@3 | 357 | ; if no space is found by the end of the table, exit |
paul@3 | 358 | |
paul@3 | 359 | cpy #TASK_TABLE_LENGTH |
paul@3 | 360 | bpl no_new_task |
paul@4 | 361 | jmp check_new_task |
paul@3 | 362 | |
paul@3 | 363 | add_new_task: |
paul@3 | 364 | |
paul@3 | 365 | ; copy the task structure location to the table |
paul@3 | 366 | |
paul@4 | 367 | sei |
paul@5 | 368 | lda ARG0H |
paul@3 | 369 | sta tasks, y |
paul@3 | 370 | dey |
paul@5 | 371 | lda ARG0 |
paul@3 | 372 | sta tasks, y |
paul@4 | 373 | cli |
paul@3 | 374 | |
paul@5 | 375 | .invoke return |
paul@3 | 376 | |
paul@3 | 377 | no_new_task: |
paul@5 | 378 | .invoke return |
paul@3 | 379 | |
paul@3 | 380 | |
paul@3 | 381 | |
paul@4 | 382 | ; remove a task from the table |
paul@4 | 383 | ; |
paul@4 | 384 | ; A: task offset |
paul@4 | 385 | ; affects: A, Y |
paul@4 | 386 | |
paul@4 | 387 | remove_task: |
paul@4 | 388 | |
paul@4 | 389 | ; zero out the table entry |
paul@4 | 390 | |
paul@4 | 391 | tay |
paul@4 | 392 | sei |
paul@4 | 393 | lda #0 |
paul@4 | 394 | sta tasks, y |
paul@4 | 395 | iny |
paul@4 | 396 | sta tasks, y |
paul@4 | 397 | cli |
paul@5 | 398 | .invoke return |
paul@5 | 399 | |
paul@4 | 400 | |
paul@4 | 401 | |
paul@2 | 402 | ; example tasks |
paul@2 | 403 | |
paul@2 | 404 | first_task: |
paul@5 | 405 | .word 0 ; user stack pointer |
paul@2 | 406 | .byte 0 ; currently unused |
paul@2 | 407 | .byte 0 ; saved flags |
paul@2 | 408 | .word first_task_start ; saved PC |
paul@2 | 409 | first_task_start: |
paul@2 | 410 | .invoke add16 1, $7000 |
paul@2 | 411 | jmp first_task_start |
paul@2 | 412 | |
paul@3 | 413 | |
paul@3 | 414 | |
paul@2 | 415 | second_task: |
paul@5 | 416 | .word 0 ; user stack pointer |
paul@2 | 417 | .byte 0 ; currently unused |
paul@2 | 418 | .byte 0 ; saved flags |
paul@2 | 419 | .word second_task_start ; saved PC |
paul@2 | 420 | second_task_start: |
paul@2 | 421 | .invoke add16 1, $7008 |
paul@2 | 422 | jmp second_task_start |
paul@2 | 423 | |
paul@4 | 424 | |
paul@4 | 425 | |
paul@4 | 426 | third_task: |
paul@5 | 427 | .word third_task_stack_base ; user stack pointer |
paul@4 | 428 | .byte 0 ; currently unused |
paul@4 | 429 | .byte 0 ; saved flags |
paul@4 | 430 | .word third_task_start ; saved PC |
paul@4 | 431 | third_task_start: |
paul@4 | 432 | .invoke store16 0, $7010 |
paul@4 | 433 | ldx #0 |
paul@4 | 434 | _loop: |
paul@4 | 435 | lda $7010 |
paul@4 | 436 | cmp #$ff |
paul@4 | 437 | bne _continue |
paul@4 | 438 | lda $7011 |
paul@4 | 439 | cmp #$ff |
paul@4 | 440 | bne _continue |
paul@4 | 441 | txa |
paul@5 | 442 | .invoke call remove_task |
paul@4 | 443 | inx |
paul@4 | 444 | _continue: |
paul@4 | 445 | .invoke add16 1, $7010 |
paul@4 | 446 | jmp _loop |
paul@5 | 447 | third_task_stack: |
paul@5 | 448 | .word 0 |
paul@5 | 449 | .word 0 |
paul@5 | 450 | .word 0 |
paul@5 | 451 | .word 0 |
paul@5 | 452 | .word 0 |
paul@5 | 453 | .word 0 |
paul@5 | 454 | third_task_stack_base: |
paul@4 | 455 | |
paul@0 | 456 | ; vim: tabstop=4 expandtab shiftwidth=4 |