paul@0 | 1 | /* |
paul@0 | 2 | * Generate a VGA signal using a PIC32 microcontroller. |
paul@0 | 3 | * |
paul@0 | 4 | * Copyright (C) 2017 Paul Boddie <paul@boddie.org.uk> |
paul@0 | 5 | * |
paul@0 | 6 | * This program is free software: you can redistribute it and/or modify |
paul@0 | 7 | * it under the terms of the GNU General Public License as published by |
paul@0 | 8 | * the Free Software Foundation, either version 3 of the License, or |
paul@0 | 9 | * (at your option) any later version. |
paul@0 | 10 | * |
paul@0 | 11 | * This program is distributed in the hope that it will be useful, |
paul@0 | 12 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
paul@0 | 13 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
paul@0 | 14 | * GNU General Public License for more details. |
paul@0 | 15 | * |
paul@0 | 16 | * You should have received a copy of the GNU General Public License |
paul@0 | 17 | * along with this program. If not, see <http://www.gnu.org/licenses/>. |
paul@0 | 18 | */ |
paul@0 | 19 | |
paul@0 | 20 | #include "mips.h" |
paul@0 | 21 | #include "pic32.h" |
paul@35 | 22 | #include "vga.h" |
paul@0 | 23 | |
paul@0 | 24 | /* Disable JTAG functionality on pins. */ |
paul@0 | 25 | |
paul@0 | 26 | .section .devcfg0, "a" |
paul@0 | 27 | .word 0xfffffffb /* DEVCFG0<2> = JTAGEN = 0 */ |
paul@0 | 28 | |
paul@0 | 29 | /* |
paul@0 | 30 | Set the oscillator to be the FRC oscillator with PLL, with peripheral clock |
paul@21 | 31 | divided by 2, and FRCDIV+PLL selected. |
paul@0 | 32 | |
paul@0 | 33 | The watchdog timer (FWDTEN) is also disabled. |
paul@9 | 34 | |
paul@9 | 35 | The secondary oscillator pin (FSOSCEN) is disabled to avoid pin conflicts with |
paul@9 | 36 | RPB4. |
paul@0 | 37 | */ |
paul@0 | 38 | |
paul@0 | 39 | .section .devcfg1, "a" |
paul@21 | 40 | .word 0xff7fdfd9 /* DEVCFG1<23> = FWDTEN = 0; DEVCFG1<13:12> = FPBDIV<1:0> = 1; |
paul@9 | 41 | DEVCFG1<5> = FSOSCEN = 0; DEVCFG1<2:0> = FNOSC<2:0> = 001 */ |
paul@0 | 42 | |
paul@0 | 43 | /* |
paul@0 | 44 | Set the FRC oscillator PLL function with an input division of 4, an output |
paul@21 | 45 | division of 2, a multiplication of 24, yielding a multiplication of 3. |
paul@21 | 46 | |
paul@21 | 47 | The FRC is apparently at 16MHz and this produces a system clock of 48MHz. |
paul@0 | 48 | */ |
paul@0 | 49 | |
paul@0 | 50 | .section .devcfg2, "a" |
paul@21 | 51 | .word 0xfff9fffb /* DEVCFG2<18:16> = FPLLODIV<2:0> = 001; |
paul@21 | 52 | DEVCFG2<6:4> = FPLLMUL<2:0> = 111; |
paul@9 | 53 | DEVCFG2<2:0> = FPLLIDIV<2:0> = 011 */ |
paul@0 | 54 | |
paul@0 | 55 | .text |
paul@0 | 56 | .globl _start |
paul@36 | 57 | .extern init_framebuffer |
paul@35 | 58 | .extern init_framebuffer_with_pattern |
paul@41 | 59 | .extern screendata |
paul@41 | 60 | .extern fontdata |
paul@41 | 61 | .extern blit_string |
paul@41 | 62 | .extern message |
paul@0 | 63 | |
paul@0 | 64 | _start: |
paul@0 | 65 | /* |
paul@0 | 66 | Configure RAM. |
paul@0 | 67 | See: http://microchipdeveloper.com/32bit:mx-arch-exceptions-processor-initialization |
paul@0 | 68 | */ |
paul@0 | 69 | |
paul@0 | 70 | la $v0, BMXCON |
paul@10 | 71 | lw $v1, 0($v0) |
paul@10 | 72 | li $t8, ~(1 << 6) /* BMXCON<6> = BMXWSDRM = 0 */ |
paul@10 | 73 | and $v1, $v1, $t8 |
paul@10 | 74 | li $t8, ~0b111 /* BMXCON<2:0> = BMXARB<2:0> = 0 */ |
paul@10 | 75 | ori $t8, $t8, 0b010 /* BMXCON<2:0> = BMXARB<2:0> = 2 */ |
paul@10 | 76 | and $v1, $v1, $t8 |
paul@10 | 77 | sw $v1, 0($v0) |
paul@0 | 78 | |
paul@0 | 79 | /* Enable caching. */ |
paul@0 | 80 | |
paul@14 | 81 | mfc0 $v1, CP0_CONFIG |
paul@14 | 82 | li $t8, ~CONFIG_K0 |
paul@14 | 83 | and $v1, $v1, $t8 |
paul@14 | 84 | ori $v1, $v1, CONFIG_K0_CACHABLE_NONCOHERENT |
paul@14 | 85 | mtc0 $v1, CP0_CONFIG |
paul@0 | 86 | nop |
paul@0 | 87 | |
paul@0 | 88 | /* Get the RAM size. */ |
paul@0 | 89 | |
paul@3 | 90 | la $v0, BMXDRMSZ |
paul@18 | 91 | lw $t0, 0($v0) |
paul@0 | 92 | |
paul@0 | 93 | /* Initialise the stack pointer. */ |
paul@0 | 94 | |
paul@3 | 95 | li $v1, KSEG0_BASE |
paul@18 | 96 | addu $sp, $t0, $v1 /* sp = KSEG0_BASE + RAM size */ |
paul@9 | 97 | |
paul@0 | 98 | /* Initialise the globals pointer. */ |
paul@0 | 99 | |
paul@0 | 100 | lui $gp, %hi(_GLOBAL_OFFSET_TABLE_) |
paul@0 | 101 | ori $gp, $gp, %lo(_GLOBAL_OFFSET_TABLE_) |
paul@0 | 102 | |
paul@5 | 103 | /* Set pins for output. */ |
paul@0 | 104 | |
paul@0 | 105 | jal init_pins |
paul@0 | 106 | nop |
paul@0 | 107 | |
paul@15 | 108 | la $t0, PORTA |
paul@15 | 109 | li $t1, (1 << 3) /* PORTA<3> = RA3 */ |
paul@15 | 110 | sw $t1, CLR($t0) |
paul@15 | 111 | |
paul@5 | 112 | jal init_oc_pins |
paul@5 | 113 | nop |
paul@5 | 114 | |
paul@0 | 115 | /* Initialise the status register. */ |
paul@0 | 116 | |
paul@0 | 117 | jal init_interrupts |
paul@0 | 118 | nop |
paul@0 | 119 | |
paul@18 | 120 | /* Initialise framebuffer. */ |
paul@18 | 121 | |
paul@36 | 122 | la $a0, screendata |
paul@36 | 123 | jal init_framebuffer |
paul@18 | 124 | nop |
paul@18 | 125 | |
paul@18 | 126 | sync |
paul@18 | 127 | |
paul@0 | 128 | /* Initialise timer. */ |
paul@0 | 129 | |
paul@4 | 130 | jal init_timer2 |
paul@0 | 131 | nop |
paul@0 | 132 | |
paul@3 | 133 | /* Initialise DMA. */ |
paul@3 | 134 | |
paul@3 | 135 | jal init_dma |
paul@3 | 136 | nop |
paul@3 | 137 | |
paul@15 | 138 | /* Initialise OC1 and OC2. */ |
paul@5 | 139 | |
paul@9 | 140 | jal init_oc |
paul@3 | 141 | nop |
paul@3 | 142 | |
paul@34 | 143 | /* Initialise the display state. */ |
paul@34 | 144 | |
paul@34 | 145 | li $s0, 0 /* line counter */ |
paul@34 | 146 | la $s1, vbp_active /* current event */ |
paul@38 | 147 | li $s2, SCREEN_BASE /* line address */ |
paul@38 | 148 | li $s3, SCREEN_BASE /* screen address */ |
paul@38 | 149 | |
paul@38 | 150 | /* Save the state for retrieval in the interrupt handler. */ |
paul@38 | 151 | |
paul@38 | 152 | li $k0, IRQ_STACK_LIMIT |
paul@38 | 153 | sw $s0, -44($k0) |
paul@38 | 154 | sw $s1, -48($k0) |
paul@38 | 155 | sw $s2, -52($k0) |
paul@38 | 156 | sw $s3, -56($k0) |
paul@34 | 157 | |
paul@0 | 158 | /* Enable interrupts and loop. */ |
paul@0 | 159 | |
paul@0 | 160 | jal enable_interrupts |
paul@0 | 161 | nop |
paul@0 | 162 | |
paul@0 | 163 | jal handle_error_level |
paul@0 | 164 | nop |
paul@0 | 165 | |
paul@3 | 166 | /* Main program. */ |
paul@3 | 167 | |
paul@39 | 168 | li $a1, (3 << 24) /* counter ~= 50000000 */ |
paul@39 | 169 | li $a2, 0xffffff /* test counter at every 1/4 of range */ |
paul@39 | 170 | move $t2, $zero /* picture to show */ |
paul@3 | 171 | |
paul@3 | 172 | /* Monitoring loop. */ |
paul@0 | 173 | loop: |
paul@3 | 174 | addiu $a1, $a1, -1 /* counter -= 1 */ |
paul@39 | 175 | and $t1, $a2, $a1 |
paul@39 | 176 | bnez $t1, loop |
paul@0 | 177 | nop |
paul@0 | 178 | |
paul@15 | 179 | la $t0, PORTA |
paul@15 | 180 | li $t1, (1 << 3) /* PORTA<3> = RA3 */ |
paul@3 | 181 | sw $t1, INV($t0) |
paul@0 | 182 | |
paul@39 | 183 | bnez $a1, loop /* until counter == 0 */ |
paul@39 | 184 | nop |
paul@39 | 185 | |
paul@39 | 186 | bnez $t2, _picture1 |
paul@39 | 187 | nop |
paul@39 | 188 | |
paul@39 | 189 | /* Show picture 0. */ |
paul@39 | 190 | |
paul@39 | 191 | la $a0, screendata |
paul@39 | 192 | jal init_framebuffer |
paul@39 | 193 | nop |
paul@41 | 194 | |
paul@41 | 195 | la $a0, message0 |
paul@41 | 196 | li $a1, SCREEN_BASE_KSEG0 |
paul@41 | 197 | jal blit_string |
paul@41 | 198 | nop |
paul@41 | 199 | |
paul@39 | 200 | li $t2, 1 |
paul@39 | 201 | j _next |
paul@39 | 202 | nop |
paul@39 | 203 | |
paul@39 | 204 | _picture1: |
paul@39 | 205 | /* Show picture 1. */ |
paul@39 | 206 | |
paul@39 | 207 | jal init_framebuffer_with_pattern |
paul@39 | 208 | nop |
paul@41 | 209 | |
paul@41 | 210 | la $a0, message1 |
paul@41 | 211 | li $a1, SCREEN_BASE_KSEG0 |
paul@41 | 212 | jal blit_string |
paul@41 | 213 | nop |
paul@41 | 214 | |
paul@39 | 215 | move $t2, $zero |
paul@39 | 216 | |
paul@0 | 217 | _next: |
paul@39 | 218 | li $a1, (3 << 24) /* counter ~= 50000000 */ |
paul@39 | 219 | li $a2, 0xffffff /* test counter at every 1/4 of range */ |
paul@0 | 220 | j loop |
paul@0 | 221 | nop |
paul@0 | 222 | |
paul@0 | 223 | |
paul@0 | 224 | |
paul@0 | 225 | init_pins: |
paul@1 | 226 | /* DEVCFG0<2> needs setting to 0 before the program is run. */ |
paul@0 | 227 | |
paul@3 | 228 | la $v0, CFGCON |
paul@0 | 229 | li $v1, (1 << 3) /* CFGCON<3> = JTAGEN = 0 */ |
paul@0 | 230 | sw $v1, CLR($v0) |
paul@0 | 231 | |
paul@3 | 232 | init_outputs: |
paul@3 | 233 | /* Remove analogue features from pins. */ |
paul@3 | 234 | |
paul@3 | 235 | la $v0, ANSELA |
paul@3 | 236 | sw $zero, 0($v0) /* ANSELA = 0 */ |
paul@3 | 237 | la $v0, ANSELB |
paul@3 | 238 | sw $zero, 0($v0) /* ANSELB = 0 */ |
paul@3 | 239 | |
paul@3 | 240 | la $v0, TRISA |
paul@3 | 241 | sw $zero, 0($v0) |
paul@0 | 242 | la $v0, TRISB |
paul@3 | 243 | sw $zero, 0($v0) |
paul@3 | 244 | |
paul@9 | 245 | la $v0, PORTA |
paul@9 | 246 | sw $zero, 0($v0) |
paul@9 | 247 | la $v0, PORTB |
paul@9 | 248 | sw $zero, 0($v0) |
paul@0 | 249 | |
paul@3 | 250 | jr $ra |
paul@0 | 251 | nop |
paul@0 | 252 | |
paul@0 | 253 | |
paul@0 | 254 | |
paul@0 | 255 | /* Initialisation routines. */ |
paul@0 | 256 | |
paul@4 | 257 | init_timer2: |
paul@0 | 258 | |
paul@4 | 259 | /* Initialise Timer2 interrupt. */ |
paul@0 | 260 | |
paul@4 | 261 | la $v0, T2CON |
paul@4 | 262 | sw $zero, 0($v0) /* T2CON = 0 */ |
paul@0 | 263 | nop |
paul@0 | 264 | |
paul@4 | 265 | la $v0, TMR2 |
paul@4 | 266 | sw $zero, 0($v0) /* TMR2 = 0 */ |
paul@5 | 267 | |
paul@4 | 268 | la $v0, PR2 |
paul@0 | 269 | li $v1, HFREQ_LIMIT |
paul@4 | 270 | sw $v1, 0($v0) /* PR2 = HFREQ_LIMIT */ |
paul@0 | 271 | |
paul@4 | 272 | /* Initialise Timer2 interrupt. */ |
paul@0 | 273 | |
paul@0 | 274 | la $v0, IFS0 |
paul@4 | 275 | li $v1, (1 << 9) |
paul@5 | 276 | sw $v1, CLR($v0) /* T2IF = 0 */ |
paul@5 | 277 | |
paul@4 | 278 | la $v0, IPC2 |
paul@5 | 279 | li $v1, 0b11111 |
paul@5 | 280 | sw $v1, CLR($v0) /* T2IP, T2IS = 0 */ |
paul@5 | 281 | |
paul@4 | 282 | la $v0, IPC2 |
paul@5 | 283 | li $v1, 0b11111 |
paul@5 | 284 | sw $v1, SET($v0) /* T2IP = 7; T2IS = 3 */ |
paul@5 | 285 | |
paul@0 | 286 | la $v0, IEC0 |
paul@4 | 287 | li $v1, (1 << 9) |
paul@5 | 288 | sw $v1, SET($v0) /* T2IE = 1 */ |
paul@0 | 289 | |
paul@0 | 290 | /* Start timer. */ |
paul@0 | 291 | |
paul@4 | 292 | la $v0, T2CON |
paul@5 | 293 | li $v1, (1 << 15) |
paul@5 | 294 | sw $v1, SET($v0) /* ON = 1 */ |
paul@5 | 295 | |
paul@5 | 296 | jr $ra |
paul@5 | 297 | nop |
paul@5 | 298 | |
paul@5 | 299 | |
paul@5 | 300 | |
paul@5 | 301 | /* |
paul@5 | 302 | Output compare initialisation. |
paul@5 | 303 | |
paul@15 | 304 | Timer2 will be used to trigger two events using OC1: one initiating the hsync |
paul@9 | 305 | pulse, and one terminating the pulse. The pulse should appear after the line |
paul@9 | 306 | data has been transferred using DMA, but this is achieved by just choosing |
paul@9 | 307 | suitable start and end values. |
paul@5 | 308 | |
paul@9 | 309 | Using OC2, Timer 2 triggers a level shifting event and OC2 is reconfigured to |
paul@9 | 310 | reverse the level at a later point. |
paul@5 | 311 | */ |
paul@5 | 312 | |
paul@9 | 313 | init_oc: |
paul@15 | 314 | /* Disable OC1 interrupts. */ |
paul@9 | 315 | |
paul@9 | 316 | la $v0, IEC0 |
paul@15 | 317 | li $v1, (1 << 7) /* IEC0<7> = OC1IE = 0 */ |
paul@9 | 318 | sw $v1, CLR($v0) |
paul@9 | 319 | |
paul@9 | 320 | la $v0, IFS0 |
paul@15 | 321 | li $v1, (1 << 7) /* IFS0<7> = OC1IF = 0 */ |
paul@9 | 322 | sw $v1, CLR($v0) |
paul@9 | 323 | |
paul@15 | 324 | /* Initialise OC1. */ |
paul@9 | 325 | |
paul@15 | 326 | la $v0, OC1CON |
paul@15 | 327 | li $v1, 0b101 /* OC1CON<2:0> = OCM<2:0> = 101 (dual compare, continuous pulse) */ |
paul@9 | 328 | sw $v1, 0($v0) |
paul@9 | 329 | |
paul@9 | 330 | /* Pulse start and end. */ |
paul@9 | 331 | |
paul@15 | 332 | la $v0, OC1R |
paul@9 | 333 | li $v1, HSYNC_END /* HSYNC_START for positive polarity */ |
paul@9 | 334 | sw $v1, 0($v0) |
paul@9 | 335 | |
paul@15 | 336 | la $v0, OC1RS |
paul@9 | 337 | li $v1, HSYNC_START /* HSYNC_END for positive polarity */ |
paul@9 | 338 | sw $v1, 0($v0) |
paul@9 | 339 | |
paul@15 | 340 | /* OC1 is enabled. */ |
paul@9 | 341 | |
paul@15 | 342 | la $v0, OC1CON |
paul@9 | 343 | li $v1, (1 << 15) |
paul@9 | 344 | sw $v1, SET($v0) |
paul@9 | 345 | |
paul@9 | 346 | /* Disable OC2 interrupts. */ |
paul@5 | 347 | |
paul@5 | 348 | la $v0, IEC0 |
paul@5 | 349 | li $v1, (1 << 12) /* IEC0<12> = OC2IE = 0 */ |
paul@5 | 350 | sw $v1, CLR($v0) |
paul@5 | 351 | |
paul@5 | 352 | la $v0, IFS0 |
paul@5 | 353 | li $v1, (1 << 12) /* IFS0<12> = OC2IF = 0 */ |
paul@5 | 354 | sw $v1, CLR($v0) |
paul@5 | 355 | |
paul@5 | 356 | /* Initialise OC2. */ |
paul@5 | 357 | |
paul@5 | 358 | la $v0, OC2CON |
paul@9 | 359 | li $v1, 0b010 /* OC2CON<2:0> = OCM<2:0> = 010 (single compare, output driven low) */ |
paul@5 | 360 | sw $v1, 0($v0) |
paul@5 | 361 | |
paul@9 | 362 | /* Set pulse position. */ |
paul@5 | 363 | |
paul@5 | 364 | la $v0, OC2R |
paul@9 | 365 | sw $zero, 0($v0) |
paul@5 | 366 | |
paul@9 | 367 | /* Enable OC2 later. */ |
paul@5 | 368 | |
paul@5 | 369 | jr $ra |
paul@5 | 370 | nop |
paul@5 | 371 | |
paul@5 | 372 | |
paul@5 | 373 | init_oc_pins: |
paul@5 | 374 | /* Unlock the configuration register bits. */ |
paul@5 | 375 | |
paul@5 | 376 | la $v0, SYSKEY |
paul@5 | 377 | sw $zero, 0($v0) |
paul@5 | 378 | li $v1, 0xAA996655 |
paul@5 | 379 | sw $v1, 0($v0) |
paul@5 | 380 | li $v1, 0x556699AA |
paul@5 | 381 | sw $v1, 0($v0) |
paul@5 | 382 | |
paul@5 | 383 | la $v0, CFGCON |
paul@5 | 384 | lw $t8, 0($v0) |
paul@5 | 385 | li $v1, (1 << 13) /* IOLOCK = 0 */ |
paul@5 | 386 | sw $v1, CLR($v0) |
paul@5 | 387 | |
paul@15 | 388 | /* Map OC1 to RPA0. */ |
paul@9 | 389 | |
paul@15 | 390 | la $v0, RPA0R |
paul@15 | 391 | li $v1, 0b0101 /* RPA0R<3:0> = 0101 (OC1) */ |
paul@9 | 392 | sw $v1, 0($v0) |
paul@9 | 393 | |
paul@15 | 394 | /* Map OC2 to RPA1. */ |
paul@5 | 395 | |
paul@15 | 396 | la $v0, RPA1R |
paul@15 | 397 | li $v1, 0b0101 /* RPA1R<3:0> = 0101 (OC2) */ |
paul@5 | 398 | sw $v1, 0($v0) |
paul@5 | 399 | |
paul@5 | 400 | la $v0, CFGCON |
paul@5 | 401 | sw $t8, 0($v0) |
paul@5 | 402 | |
paul@5 | 403 | /* Lock the oscillator control register again. */ |
paul@5 | 404 | |
paul@5 | 405 | la $v0, SYSKEY |
paul@5 | 406 | li $v1, 0x33333333 |
paul@5 | 407 | sw $v1, 0($v0) |
paul@0 | 408 | |
paul@0 | 409 | jr $ra |
paul@0 | 410 | nop |
paul@1 | 411 | |
paul@1 | 412 | |
paul@1 | 413 | |
paul@5 | 414 | /* |
paul@5 | 415 | Direct Memory Access initialisation. |
paul@3 | 416 | |
paul@15 | 417 | Write 160 pixels to PORTB for the line data. This is initiated by a timer |
paul@9 | 418 | interrupt. Upon completion of the transfer, a DMA interrupt initiates the |
paul@9 | 419 | address update routine, changing the source address of the DMA channel. |
paul@3 | 420 | */ |
paul@3 | 421 | |
paul@3 | 422 | init_dma: |
paul@3 | 423 | /* Disable DMA interrupts. */ |
paul@1 | 424 | |
paul@3 | 425 | la $v0, IEC1 |
paul@15 | 426 | li $v1, (3 << 28) /* IEC1<29:28> = DMA1IE, DMA0IE = 0 */ |
paul@3 | 427 | sw $v1, CLR($v0) |
paul@3 | 428 | |
paul@3 | 429 | /* Clear DMA interrupt flags. */ |
paul@1 | 430 | |
paul@3 | 431 | la $v0, IFS1 |
paul@15 | 432 | li $v1, (3 << 28) /* IFS1<29:28> = DMA1IF, DMA0IF = 0 */ |
paul@3 | 433 | sw $v1, CLR($v0) |
paul@3 | 434 | |
paul@3 | 435 | /* Enable DMA. */ |
paul@3 | 436 | |
paul@3 | 437 | la $v0, DMACON |
paul@3 | 438 | li $v1, (1 << 15) |
paul@1 | 439 | sw $v1, SET($v0) |
paul@1 | 440 | |
paul@3 | 441 | /* |
paul@5 | 442 | Initialise a line channel. |
paul@5 | 443 | The line channel will be channel 0 (x = 0). |
paul@3 | 444 | |
paul@3 | 445 | Specify a priority of 3: |
paul@3 | 446 | DCHxCON<1:0> = CHPRI<1:0> = 3 |
paul@3 | 447 | |
paul@15 | 448 | Auto-enable the channel: |
paul@3 | 449 | DCHxCON<4> = CHAEN = 1 |
paul@3 | 450 | */ |
paul@3 | 451 | |
paul@3 | 452 | la $v0, DCH0CON |
paul@3 | 453 | li $v1, 0b10011 |
paul@3 | 454 | sw $v1, 0($v0) |
paul@3 | 455 | |
paul@5 | 456 | /* |
paul@15 | 457 | Initialise a level reset channel. |
paul@15 | 458 | The reset channel will be channel 1 (x = 1). |
paul@15 | 459 | |
paul@15 | 460 | Specify a priority of 3: |
paul@15 | 461 | DCHxCON<1:0> = CHPRI<1:0> = 3 |
paul@15 | 462 | |
paul@15 | 463 | Chain the channel to channel 0: |
paul@15 | 464 | DCHxCON<5> = CHCHN = 1 |
paul@15 | 465 | |
paul@15 | 466 | Allow the channel to receive events when disabled: |
paul@15 | 467 | DCHxCON<6> = CHAED = 1 |
paul@15 | 468 | */ |
paul@15 | 469 | |
paul@15 | 470 | la $v0, DCH1CON |
paul@15 | 471 | li $v1, 0b1100011 |
paul@15 | 472 | sw $v1, 0($v0) |
paul@15 | 473 | |
paul@15 | 474 | /* |
paul@5 | 475 | Initiate channel transfers when the initiating interrupt condition |
paul@5 | 476 | occurs: |
paul@9 | 477 | DCHxECON<15:8> = CHSIRQ<7:0> = timer 2 interrupt |
paul@11 | 478 | DCHxECON<4> = SIRQEN = 1 |
paul@20 | 479 | |
paul@20 | 480 | For now, however, prevent initiation by not setting SIRQEN. |
paul@5 | 481 | */ |
paul@3 | 482 | |
paul@3 | 483 | la $v0, DCH0ECON |
paul@20 | 484 | li $v1, (9 << 8) |
paul@3 | 485 | sw $v1, 0($v0) |
paul@1 | 486 | |
paul@3 | 487 | /* |
paul@15 | 488 | Initiate reset channel transfer when channel 0 is finished: |
paul@15 | 489 | DCHxECON<15:8> = CHSIRQ<7:0> = channel 0 interrupt |
paul@15 | 490 | DCHxECON<4> = SIRQEN = 1 |
paul@15 | 491 | */ |
paul@15 | 492 | |
paul@15 | 493 | la $v0, DCH1ECON |
paul@15 | 494 | li $v1, (60 << 8) | (1 << 4) |
paul@15 | 495 | sw $v1, 0($v0) |
paul@15 | 496 | |
paul@15 | 497 | /* |
paul@15 | 498 | The line channel has a cell size of the number bytes in a line: |
paul@9 | 499 | DCHxCSIZ<15:0> = CHCSIZ<15:0> = LINE_LENGTH |
paul@3 | 500 | */ |
paul@3 | 501 | |
paul@3 | 502 | la $v0, DCH0CSIZ |
paul@9 | 503 | li $v1, LINE_LENGTH |
paul@3 | 504 | sw $v1, 0($v0) |
paul@1 | 505 | |
paul@3 | 506 | /* |
paul@15 | 507 | The reset channel has a cell size of a single zero byte: |
paul@15 | 508 | DCHxCSIZ<15:0> = CHCSIZ<15:0> = LINE_LENGTH |
paul@15 | 509 | */ |
paul@15 | 510 | |
paul@15 | 511 | la $v0, DCH1CSIZ |
paul@15 | 512 | li $v1, 1 |
paul@15 | 513 | sw $v1, 0($v0) |
paul@15 | 514 | |
paul@15 | 515 | /* |
paul@11 | 516 | The source has a size identical to the cell size: |
paul@11 | 517 | DCHxSSIZ<15:0> = CHSSIZ<15:0> = LINE_LENGTH |
paul@3 | 518 | */ |
paul@3 | 519 | |
paul@3 | 520 | la $v0, DCH0SSIZ |
paul@9 | 521 | li $v1, LINE_LENGTH |
paul@3 | 522 | sw $v1, 0($v0) |
paul@3 | 523 | |
paul@15 | 524 | la $v0, DCH1SSIZ |
paul@15 | 525 | li $v1, 1 |
paul@15 | 526 | sw $v1, 0($v0) |
paul@15 | 527 | |
paul@3 | 528 | /* |
paul@5 | 529 | The source address is the physical address of the line data: |
paul@11 | 530 | DCHxSSA = physical(line data address) |
paul@3 | 531 | */ |
paul@1 | 532 | |
paul@3 | 533 | la $v0, DCH0SSA |
paul@38 | 534 | li $v1, SCREEN_BASE |
paul@38 | 535 | sw $v1, 0($v0) |
paul@3 | 536 | |
paul@3 | 537 | /* |
paul@15 | 538 | For the reset channel, a single byte of zero is transferred: |
paul@15 | 539 | DCHxSSA = physical(zero data address) |
paul@15 | 540 | */ |
paul@15 | 541 | |
paul@15 | 542 | la $v0, DCH1SSA |
paul@15 | 543 | la $v1, zerodata |
paul@15 | 544 | li $t8, KSEG0_BASE |
paul@15 | 545 | subu $v1, $v1, $t8 |
paul@15 | 546 | sw $v1, 0($v0) |
paul@15 | 547 | |
paul@15 | 548 | /* |
paul@11 | 549 | The destination has a size of 1 byte: |
paul@3 | 550 | DCHxDSIZ<15:0> = CHDSIZ<15:0> = 1 |
paul@3 | 551 | */ |
paul@3 | 552 | |
paul@3 | 553 | la $v0, DCH0DSIZ |
paul@3 | 554 | li $v1, 1 |
paul@3 | 555 | sw $v1, 0($v0) |
paul@3 | 556 | |
paul@15 | 557 | la $v0, DCH1DSIZ |
paul@15 | 558 | sw $v1, 0($v0) |
paul@15 | 559 | |
paul@3 | 560 | /* |
paul@15 | 561 | The destination address is the physical address of PORTB: |
paul@15 | 562 | DCHxDSA = physical(PORTB) |
paul@3 | 563 | */ |
paul@3 | 564 | |
paul@5 | 565 | la $v0, DCH0DSA |
paul@15 | 566 | li $v1, PORTB |
paul@3 | 567 | li $t8, KSEG1_BASE |
paul@3 | 568 | subu $v1, $v1, $t8 |
paul@3 | 569 | sw $v1, 0($v0) |
paul@3 | 570 | |
paul@15 | 571 | la $v0, DCH1DSA |
paul@15 | 572 | sw $v1, 0($v0) |
paul@15 | 573 | |
paul@7 | 574 | /* |
paul@7 | 575 | Use the block transfer completion interrupt to indicate when the source |
paul@7 | 576 | address can be updated. |
paul@7 | 577 | */ |
paul@7 | 578 | |
paul@3 | 579 | la $v0, DCH0INT |
paul@7 | 580 | li $v1, (1 << 19) /* CHBCIE = 1 */ |
paul@7 | 581 | sw $v1, 0($v0) |
paul@7 | 582 | |
paul@7 | 583 | /* Enable interrupt for address updating. */ |
paul@7 | 584 | |
paul@7 | 585 | la $v0, IPC10 |
paul@7 | 586 | li $v1, 0b11111 /* DMA0IP, DMA0IS = 0 */ |
paul@7 | 587 | sw $v1, CLR($v0) |
paul@7 | 588 | |
paul@7 | 589 | la $v0, IPC10 |
paul@7 | 590 | li $v1, 0b11111 /* DMA0IP = 7, DMA0IS = 3 */ |
paul@7 | 591 | sw $v1, SET($v0) |
paul@7 | 592 | |
paul@7 | 593 | la $v0, IEC1 |
paul@7 | 594 | li $v1, (1 << 28) /* IEC1<28> = DMA0IE = 1 */ |
paul@9 | 595 | sw $v1, SET($v0) |
paul@1 | 596 | |
paul@15 | 597 | /* Enable line channel. */ |
paul@3 | 598 | |
paul@3 | 599 | la $v0, DCH0CON |
paul@3 | 600 | li $v1, 0b10000000 |
paul@3 | 601 | sw $v1, SET($v0) |
paul@3 | 602 | |
paul@1 | 603 | jr $ra |
paul@1 | 604 | nop |
paul@1 | 605 | |
paul@15 | 606 | zerodata: |
paul@15 | 607 | .word 0 |
paul@15 | 608 | |
paul@1 | 609 | |
paul@1 | 610 | |
paul@9 | 611 | /* Utilities. */ |
paul@9 | 612 | |
paul@9 | 613 | handle_error_level: |
paul@9 | 614 | mfc0 $t3, CP0_STATUS |
paul@9 | 615 | li $t4, ~(STATUS_ERL | STATUS_EXL) |
paul@9 | 616 | and $t3, $t3, $t4 |
paul@9 | 617 | mtc0 $t3, CP0_STATUS |
paul@9 | 618 | jr $ra |
paul@9 | 619 | nop |
paul@9 | 620 | |
paul@9 | 621 | enable_interrupts: |
paul@9 | 622 | mfc0 $t3, CP0_STATUS |
paul@9 | 623 | li $t4, ~STATUS_IRQ /* Clear interrupt priority bits. */ |
paul@9 | 624 | and $t3, $t3, $t4 |
paul@9 | 625 | li $t4, ~STATUS_BEV /* CP0_STATUS &= ~STATUS_BEV (use non-bootloader vectors) */ |
paul@9 | 626 | and $t3, $t3, $t4 |
paul@9 | 627 | ori $t3, $t3, STATUS_IE |
paul@9 | 628 | mtc0 $t3, CP0_STATUS |
paul@9 | 629 | jr $ra |
paul@9 | 630 | nop |
paul@9 | 631 | |
paul@9 | 632 | init_interrupts: |
paul@9 | 633 | mfc0 $t3, CP0_DEBUG |
paul@9 | 634 | li $t4, ~DEBUG_DM |
paul@9 | 635 | and $t3, $t3, $t4 |
paul@9 | 636 | mtc0 $t3, CP0_DEBUG |
paul@9 | 637 | |
paul@9 | 638 | mfc0 $t3, CP0_STATUS |
paul@11 | 639 | li $t4, STATUS_BEV /* BEV = 1 or EBASE cannot be set */ |
paul@9 | 640 | or $t3, $t3, $t4 |
paul@9 | 641 | mtc0 $t3, CP0_STATUS |
paul@9 | 642 | |
paul@9 | 643 | la $t3, exception_handler |
paul@9 | 644 | mtc0 $t3, CP0_EBASE /* EBASE = exception_handler */ |
paul@9 | 645 | |
paul@9 | 646 | li $t3, 0x20 /* Must be non-zero or the CPU gets upset */ |
paul@9 | 647 | mtc0 $t3, CP0_INTCTL |
paul@9 | 648 | |
paul@9 | 649 | li $t3, CAUSE_IV /* IV = 1 (use EBASE+0x200 for interrupts) */ |
paul@9 | 650 | mtc0 $t3, CP0_CAUSE |
paul@9 | 651 | |
paul@9 | 652 | jr $ra |
paul@9 | 653 | nop |
paul@9 | 654 | |
paul@9 | 655 | |
paul@9 | 656 | |
paul@9 | 657 | /* Exception servicing. */ |
paul@9 | 658 | |
paul@9 | 659 | .section .flash, "a" |
paul@9 | 660 | |
paul@33 | 661 | /* TLB error servicing. */ |
paul@33 | 662 | |
paul@33 | 663 | tlb_handler: |
paul@9 | 664 | j exception_handler |
paul@9 | 665 | nop |
paul@9 | 666 | |
paul@9 | 667 | |
paul@9 | 668 | |
paul@33 | 669 | /* General exception servicing. */ |
paul@33 | 670 | |
paul@33 | 671 | .org 0x180 |
paul@33 | 672 | |
paul@33 | 673 | exception_handler: |
paul@33 | 674 | j exc_handler |
paul@33 | 675 | nop |
paul@33 | 676 | |
paul@33 | 677 | |
paul@9 | 678 | /* Interrupt servicing. */ |
paul@9 | 679 | |
paul@9 | 680 | .org 0x200 |
paul@9 | 681 | |
paul@9 | 682 | interrupt_handler: |
paul@9 | 683 | |
paul@38 | 684 | /* Store affected registers. */ |
paul@38 | 685 | |
paul@38 | 686 | li $k0, IRQ_STACK_LIMIT |
paul@38 | 687 | sw $v0, -4($k0) |
paul@38 | 688 | sw $v1, -8($k0) |
paul@38 | 689 | sw $s0, -12($k0) |
paul@38 | 690 | sw $s1, -16($k0) |
paul@38 | 691 | sw $s2, -20($k0) |
paul@38 | 692 | sw $s3, -24($k0) |
paul@38 | 693 | sw $t8, -28($k0) |
paul@38 | 694 | sw $ra, -32($k0) |
paul@38 | 695 | sw $sp, -36($k0) |
paul@38 | 696 | |
paul@38 | 697 | /* Load state. */ |
paul@38 | 698 | |
paul@38 | 699 | lw $s0, -44($k0) |
paul@38 | 700 | lw $s1, -48($k0) |
paul@38 | 701 | lw $s2, -52($k0) |
paul@38 | 702 | lw $s3, -56($k0) |
paul@38 | 703 | |
paul@38 | 704 | li $sp, IRQ_STACK_TOP |
paul@38 | 705 | |
paul@9 | 706 | /* Check for a timer interrupt condition. */ |
paul@9 | 707 | |
paul@9 | 708 | la $v0, IFS0 |
paul@9 | 709 | lw $v1, 0($v0) |
paul@9 | 710 | andi $v1, $v1, (1 << 9) /* T2IF */ |
paul@9 | 711 | beqz $v1, irq_dma |
paul@9 | 712 | nop |
paul@9 | 713 | |
paul@44 | 714 | /* Clear the timer interrupt condition. */ |
paul@44 | 715 | |
paul@44 | 716 | li $v1, (1 << 9) /* IFS0<9> = T2IF = 0 */ |
paul@44 | 717 | sw $v1, CLR($v0) |
paul@44 | 718 | |
paul@9 | 719 | /* Increment the line counter. */ |
paul@9 | 720 | |
paul@9 | 721 | addiu $s0, $s0, 1 |
paul@9 | 722 | |
paul@9 | 723 | /* Jump to the event handler. */ |
paul@9 | 724 | |
paul@9 | 725 | jalr $s1 |
paul@9 | 726 | nop |
paul@9 | 727 | |
paul@9 | 728 | irq_dma: |
paul@9 | 729 | /* Check for a DMA interrupt condition. */ |
paul@9 | 730 | |
paul@9 | 731 | la $v0, IFS1 |
paul@9 | 732 | lw $v1, 0($v0) |
paul@9 | 733 | li $t8, (1 << 28) /* DMA0IF */ |
paul@9 | 734 | and $v1, $v1, $t8 |
paul@9 | 735 | beqz $v1, irq_exit |
paul@9 | 736 | nop |
paul@9 | 737 | |
paul@44 | 738 | /* Clear the DMA interrupt condition. */ |
paul@44 | 739 | |
paul@44 | 740 | li $v1, (1 << 28) /* IFS1<28> = DMA0IF = 0 */ |
paul@44 | 741 | sw $v1, CLR($v0) |
paul@44 | 742 | |
paul@9 | 743 | /* Test the block transfer completion interrupt flag. */ |
paul@9 | 744 | |
paul@9 | 745 | la $v0, DCH0INT |
paul@9 | 746 | lw $v1, 0($v0) |
paul@9 | 747 | andi $v1, $v1, (1 << 3) /* CHBCIF */ |
paul@44 | 748 | beqz $v1, irq_exit |
paul@9 | 749 | nop |
paul@9 | 750 | |
paul@9 | 751 | /* Clear the block transfer completion interrupt flag. */ |
paul@9 | 752 | |
paul@9 | 753 | li $v1, (1 << 3) /* CHBCIF = 0 */ |
paul@9 | 754 | sw $v1, CLR($v0) |
paul@9 | 755 | |
paul@9 | 756 | /* |
paul@9 | 757 | Update the line data address if the line counter (referring to the |
paul@9 | 758 | next line) is even. |
paul@9 | 759 | */ |
paul@9 | 760 | |
paul@9 | 761 | andi $t8, $s0, 1 |
paul@44 | 762 | bnez $t8, irq_exit |
paul@9 | 763 | nop |
paul@9 | 764 | |
paul@9 | 765 | /* Reference the next line and update the DMA source address. */ |
paul@9 | 766 | |
paul@9 | 767 | addiu $s2, $s2, LINE_LENGTH |
paul@9 | 768 | |
paul@9 | 769 | /* Test for wraparound. */ |
paul@9 | 770 | |
paul@38 | 771 | li $t8, (SCREEN_BASE + SCREEN_SIZE) |
paul@9 | 772 | sltu $t8, $s2, $t8 |
paul@9 | 773 | bnez $t8, irq_dma_update |
paul@9 | 774 | nop |
paul@9 | 775 | |
paul@9 | 776 | /* Reset the source address. */ |
paul@9 | 777 | |
paul@38 | 778 | li $s2, SCREEN_BASE |
paul@9 | 779 | |
paul@9 | 780 | irq_dma_update: |
paul@9 | 781 | |
paul@42 | 782 | /* Disable line channel. */ |
paul@42 | 783 | |
paul@42 | 784 | la $v0, DCH0CON |
paul@42 | 785 | li $v1, 0b10000000 |
paul@42 | 786 | sw $v1, CLR($v0) |
paul@42 | 787 | |
paul@42 | 788 | /* Update the source address. */ |
paul@42 | 789 | |
paul@9 | 790 | la $v0, DCH0SSA |
paul@9 | 791 | sw $s2, 0($v0) |
paul@9 | 792 | |
paul@42 | 793 | /* Enable line channel. */ |
paul@42 | 794 | |
paul@42 | 795 | la $v0, DCH0CON |
paul@42 | 796 | sw $v1, SET($v0) |
paul@42 | 797 | |
paul@9 | 798 | irq_exit: |
paul@38 | 799 | /* Save state. */ |
paul@38 | 800 | |
paul@38 | 801 | li $k0, IRQ_STACK_LIMIT |
paul@38 | 802 | sw $s0, -44($k0) |
paul@38 | 803 | sw $s1, -48($k0) |
paul@38 | 804 | sw $s2, -52($k0) |
paul@38 | 805 | sw $s3, -56($k0) |
paul@38 | 806 | |
paul@38 | 807 | /* Restore affected registers. */ |
paul@38 | 808 | |
paul@38 | 809 | lw $v0, -4($k0) |
paul@38 | 810 | lw $v1, -8($k0) |
paul@38 | 811 | lw $s0, -12($k0) |
paul@38 | 812 | lw $s1, -16($k0) |
paul@38 | 813 | lw $s2, -20($k0) |
paul@38 | 814 | lw $s3, -24($k0) |
paul@38 | 815 | lw $t8, -28($k0) |
paul@38 | 816 | lw $ra, -32($k0) |
paul@38 | 817 | lw $sp, -36($k0) |
paul@38 | 818 | |
paul@9 | 819 | eret |
paul@9 | 820 | nop |
paul@9 | 821 | |
paul@9 | 822 | |
paul@9 | 823 | |
paul@33 | 824 | exc_handler: |
paul@33 | 825 | li $t9, 0x80000000 |
paul@33 | 826 | mfc0 $t6, CP0_CAUSE |
paul@33 | 827 | nop |
paul@33 | 828 | exc_loop: |
paul@33 | 829 | and $t7, $t9, $t6 |
paul@33 | 830 | beqz $t7, exc_errorepc_zero |
paul@33 | 831 | nop |
paul@33 | 832 | exc_errorepc_one: |
paul@33 | 833 | la $v0, PORTA |
paul@33 | 834 | li $v1, (1 << 2) /* PORTA<2> = RA2 */ |
paul@33 | 835 | sw $v1, SET($v0) |
paul@33 | 836 | j exc_loop_wait |
paul@33 | 837 | nop |
paul@33 | 838 | exc_errorepc_zero: |
paul@33 | 839 | la $v0, PORTA |
paul@33 | 840 | li $v1, (1 << 3) /* PORTA<3> = RA3 */ |
paul@33 | 841 | sw $v1, SET($v0) |
paul@33 | 842 | exc_loop_wait: |
paul@33 | 843 | li $t8, 5000000 |
paul@33 | 844 | exc_loop_delay: |
paul@33 | 845 | addiu $t8, $t8, -1 |
paul@33 | 846 | bnez $t8, exc_loop_delay |
paul@33 | 847 | nop |
paul@33 | 848 | la $v0, PORTA |
paul@33 | 849 | li $v1, (3 << 2) /* PORTA<3:2> = RA3, RA2 */ |
paul@33 | 850 | sw $v1, CLR($v0) |
paul@33 | 851 | exc_loop_wait_again: |
paul@33 | 852 | li $t8, 2500000 |
paul@33 | 853 | exc_loop_delay_again: |
paul@33 | 854 | addiu $t8, $t8, -1 |
paul@33 | 855 | bnez $t8, exc_loop_delay_again |
paul@33 | 856 | nop |
paul@33 | 857 | exc_errorepc_next: |
paul@33 | 858 | srl $t9, $t9, 1 |
paul@33 | 859 | bnez $t9, exc_loop |
paul@33 | 860 | nop |
paul@33 | 861 | j exc_handler |
paul@33 | 862 | nop |
paul@33 | 863 | |
paul@33 | 864 | |
paul@33 | 865 | |
paul@9 | 866 | /* Event routines. */ |
paul@9 | 867 | |
paul@9 | 868 | /* The vertical back porch. */ |
paul@9 | 869 | |
paul@9 | 870 | vbp_active: |
paul@9 | 871 | /* Test for visible region. */ |
paul@9 | 872 | |
paul@9 | 873 | sltiu $v0, $s0, VISIBLE_START |
paul@9 | 874 | bnez $v0, _vbp_active_ret |
paul@9 | 875 | nop |
paul@9 | 876 | |
paul@9 | 877 | /* Start the visible region. */ |
paul@9 | 878 | |
paul@9 | 879 | la $s1, visible_active |
paul@9 | 880 | |
paul@17 | 881 | /* Reset the line address. */ |
paul@17 | 882 | |
paul@17 | 883 | move $s2, $s3 |
paul@17 | 884 | |
paul@43 | 885 | /* Update the source address. */ |
paul@43 | 886 | |
paul@43 | 887 | la $v0, DCH0SSA |
paul@43 | 888 | sw $s2, 0($v0) |
paul@43 | 889 | |
paul@20 | 890 | /* Enable the line channel. */ |
paul@20 | 891 | |
paul@20 | 892 | la $v0, DCH0ECON |
paul@20 | 893 | li $v1, (1 << 4) |
paul@20 | 894 | sw $v1, SET($v0) |
paul@20 | 895 | |
paul@9 | 896 | _vbp_active_ret: |
paul@9 | 897 | jr $ra |
paul@9 | 898 | nop |
paul@9 | 899 | |
paul@9 | 900 | |
paul@9 | 901 | |
paul@9 | 902 | /* The visible region. */ |
paul@9 | 903 | |
paul@9 | 904 | visible_active: |
paul@9 | 905 | /* Test for front porch. */ |
paul@9 | 906 | |
paul@9 | 907 | sltiu $v0, $s0, VFP_START |
paul@9 | 908 | bnez $v0, _visible_active_ret |
paul@9 | 909 | nop |
paul@9 | 910 | |
paul@9 | 911 | /* Start the front porch region. */ |
paul@9 | 912 | |
paul@9 | 913 | la $s1, vfp_active |
paul@9 | 914 | |
paul@20 | 915 | /* Disable the line channel. */ |
paul@20 | 916 | |
paul@20 | 917 | la $v0, DCH0ECON |
paul@20 | 918 | li $v1, (1 << 4) |
paul@20 | 919 | sw $v1, CLR($v0) |
paul@20 | 920 | |
paul@9 | 921 | _visible_active_ret: |
paul@9 | 922 | jr $ra |
paul@9 | 923 | nop |
paul@9 | 924 | |
paul@9 | 925 | |
paul@9 | 926 | |
paul@9 | 927 | /* Within the vertical front porch. */ |
paul@9 | 928 | |
paul@9 | 929 | vfp_active: |
paul@9 | 930 | /* Test for vsync. */ |
paul@9 | 931 | |
paul@9 | 932 | sltiu $v0, $s0, VSYNC_START |
paul@9 | 933 | bnez $v0, _vfp_active_ret |
paul@9 | 934 | nop |
paul@9 | 935 | |
paul@9 | 936 | /* Start the vsync. */ |
paul@9 | 937 | |
paul@9 | 938 | la $s1, vsync_active |
paul@9 | 939 | |
paul@9 | 940 | /* Bring vsync low when the next line starts. */ |
paul@9 | 941 | |
paul@9 | 942 | la $v0, OC2CON |
paul@9 | 943 | li $v1, 0b010 | (1 << 15) /* OC2CON<2:0> = OCM<2:0> = 010 (single compare, output driven low) */ |
paul@9 | 944 | sw $v1, 0($v0) |
paul@9 | 945 | |
paul@9 | 946 | _vfp_active_ret: |
paul@9 | 947 | jr $ra |
paul@9 | 948 | nop |
paul@9 | 949 | |
paul@9 | 950 | |
paul@9 | 951 | |
paul@9 | 952 | /* The vsync period. */ |
paul@9 | 953 | |
paul@9 | 954 | vsync_active: |
paul@9 | 955 | /* Test for front porch. */ |
paul@9 | 956 | |
paul@9 | 957 | sltiu $v0, $s0, VSYNC_END |
paul@9 | 958 | bnez $v0, _vsync_active_ret |
paul@9 | 959 | nop |
paul@9 | 960 | |
paul@9 | 961 | /* Start the back porch. */ |
paul@9 | 962 | |
paul@9 | 963 | move $s0, $zero |
paul@9 | 964 | la $s1, vbp_active |
paul@9 | 965 | |
paul@9 | 966 | /* Bring vsync high when the next line starts. */ |
paul@9 | 967 | |
paul@9 | 968 | la $v0, OC2CON |
paul@9 | 969 | li $v1, 0b001 | (1 << 15) /* OC2CON<2:0> = OCM<2:0> = 001 (single compare, output driven high) */ |
paul@9 | 970 | sw $v1, 0($v0) |
paul@9 | 971 | |
paul@9 | 972 | _vsync_active_ret: |
paul@9 | 973 | jr $ra |
paul@9 | 974 | nop |