clock/firmware/main.c

   1 /*
   2  *      Workshop Clock
   3  *
   4  *      (c) 2020-2023 Martin Mareš <mj@ucw.cz>
   5  */
   6
   7 #include "util.h"
   8
   9 #include <libopencm3/cm3/cortex.h>
  10 #include <libopencm3/cm3/nvic.h>
  11 #include <libopencm3/cm3/systick.h>
  12 #include <libopencm3/cm3/scb.h>
  13 #include <libopencm3/stm32/rcc.h>
  14 #include <libopencm3/stm32/desig.h>
  15 #include <libopencm3/stm32/gpio.h>
  16 #include <libopencm3/stm32/usart.h>
  17 #include <libopencm3/stm32/i2c.h>
  18 #include <libopencm3/stm32/timer.h>
  19 #include <libopencm3/usb/dfu.h>
  20 #include <libopencm3/usb/usbd.h>
  21
  22 #include <string.h>
  23
  24 static void ep82_send(u32 key_code);
  25
  26 /*** Hardware init ***/
  27
  28 static void clock_init(void)
  29 {
  30         rcc_clock_setup_pll(&rcc_hse_configs[RCC_CLOCK_HSE8_72MHZ]);
  31
  32         rcc_periph_clock_enable(RCC_GPIOA);
  33         rcc_periph_clock_enable(RCC_GPIOB);
  34         rcc_periph_clock_enable(RCC_GPIOC);
  35         rcc_periph_clock_enable(RCC_I2C1);
  36         rcc_periph_clock_enable(RCC_USART1);
  37         rcc_periph_clock_enable(RCC_USB);
  38         rcc_periph_clock_enable(RCC_TIM1);
  39
  40         rcc_periph_reset_pulse(RST_GPIOA);
  41         rcc_periph_reset_pulse(RST_GPIOB);
  42         rcc_periph_reset_pulse(RST_GPIOC);
  43         rcc_periph_reset_pulse(RST_I2C1);
  44         rcc_periph_reset_pulse(RST_USART1);
  45         rcc_periph_reset_pulse(RST_USB);
  46         rcc_periph_reset_pulse(RST_TIM1);
  47 }
  48
  49 static void gpio_init(void)
  50 {
  51         // PA9 = TXD1 for debugging console
  52         // PA10 = RXD1 for debugging console
  53         gpio_set_mode(GPIOA, GPIO_MODE_OUTPUT_50_MHZ, GPIO_CNF_OUTPUT_ALTFN_PUSHPULL, GPIO9);
  54         gpio_set_mode(GPIOA, GPIO_MODE_INPUT, GPIO_CNF_INPUT_FLOAT, GPIO10);
  55
  56         // PC13 = BluePill LED
  57         gpio_set_mode(GPIOC, GPIO_MODE_OUTPUT_50_MHZ, GPIO_CNF_OUTPUT_PUSHPULL, GPIO13);
  58         gpio_clear(GPIOC, GPIO13);
  59
  60         // PB7 = SDA for display controller
  61         // PB6 = SCL for display controller
  62         gpio_set_mode(GPIOB, GPIO_MODE_OUTPUT_50_MHZ, GPIO_CNF_OUTPUT_ALTFN_OPENDRAIN, GPIO6 | GPIO7);
  63
  64         // PA8 = SFH5110 output (5V tolerant) connected to TIM1_CH1
  65         gpio_set_mode(GPIOC, GPIO_MODE_INPUT, GPIO_CNF_INPUT_FLOAT, GPIO8);
  66 }
  67
  68 static void usart_init(void)
  69 {
  70         usart_set_baudrate(USART1, 115200);
  71         usart_set_databits(USART1, 8);
  72         usart_set_stopbits(USART1, USART_STOPBITS_1);
  73         usart_set_mode(USART1, USART_MODE_TX);
  74         usart_set_parity(USART1, USART_PARITY_NONE);
  75         usart_set_flow_control(USART1, USART_FLOWCONTROL_NONE);
  76
  77         usart_enable(USART1);
  78 }
  79
  80 /*** System ticks ***/
  81
  82 static volatile u32 ms_ticks;
  83
  84 void sys_tick_handler(void)
  85 {
  86         ms_ticks++;
  87 }
  88
  89 static void tick_init(void)
  90 {
  91         systick_set_frequency(1000, CPU_CLOCK_MHZ * 1000000);
  92         systick_counter_enable();
  93         systick_interrupt_enable();
  94 }
  95
  96 static void delay_ms(uint ms)
  97 {
  98         u32 start_ticks = ms_ticks;
  99         while (ms_ticks - start_ticks < ms)
 100                 ;
 101 }
 102
 103 /*** Display ***/
 104
 105 /*
 106  *      Display digits:
 107  *
 108  *                 ---- 40 ----
 109  *               |              |
 110  *               |              |
 111  *              20              80
 112  *               |              |
 113  *               |              |
 114  *                 ---- 10 ----
 115  *               |              |
 116  *               |              |
 117  *              08              02
 118  *               |              |
 119  *               |              |
 120  *                 ---- 04 ----
 121  *                                      (01)
 122  */
 123
 124 static byte disp[4];
 125 static byte ctrl = 0x56;
 126
 127 static const byte disp_font[] = {
 128         [0] = 0xee,
 129         [1] = 0x82,
 130         [2] = 0xdc,
 131         [3] = 0xd6,
 132         [4] = 0xb2,
 133         [5] = 0x76,
 134         [6] = 0x7e,
 135         [7] = 0xc2,
 136         [8] = 0xfe,
 137         [9] = 0xf6,
 138         [10] = 0xea,
 139         [11] = 0x3e,
 140         [12] = 0x6c,
 141         [13] = 0x9e,
 142         [14] = 0x7c,
 143         [15] = 0x78,
 144 };
 145
 146 static void display_update(void)
 147 {
 148         // debug_puts("Display update\n");
 149
 150         byte cmds[4];
 151         cmds[0] = 0;
 152         cmds[1] = ctrl;
 153         cmds[2] = ((disp[1] & 0x88) >> 3) | ((disp[1] & 0x44) >> 1) | ((disp[1] & 0x22) << 1) | ((disp[1] & 0x11) << 3);
 154         cmds[3] = disp[0];
 155         i2c_transfer7(I2C1, 0x76/2, (byte *) cmds, sizeof(cmds), NULL, 0);
 156
 157         cmds[2] = ((disp[3] & 0x88) >> 3) | ((disp[3] & 0x44) >> 1) | ((disp[3] & 0x22) << 1) | ((disp[3] & 0x11) << 3);
 158         cmds[3] = disp[2];
 159         i2c_transfer7(I2C1, 0x70/2, (byte *) cmds, sizeof(cmds), NULL, 0);
 160
 161         // debug_puts("Update done\n");
 162 }
 163
 164 static void display_init(void)
 165 {
 166         debug_puts("I2C init\n");
 167         i2c_peripheral_disable(I2C1);
 168         i2c_set_speed(I2C1, i2c_speed_sm_100k, rcc_apb1_frequency / 1000000);
 169         i2c_peripheral_enable(I2C1);
 170
 171         disp[0] = 0x10;
 172         disp[1] = 0x10;
 173         disp[2] = 0x10;
 174         disp[3] = 0x10;
 175         display_update();
 176 }
 177
 178 /*** Infrared Remote Control ***/
 179
 180 static void ir_init(void)
 181 {
 182         debug_puts("IR init\n");
 183
 184         // TIM1 will measure pulses and spaces between them with 1μs resolution
 185         timer_set_prescaler(TIM1, 71);          // 72 MHz / 72 = 1 MHz
 186         timer_set_mode(TIM1, TIM_CR1_CKD_CK_INT, TIM_CR1_CMS_EDGE, TIM_CR1_DIR_UP);
 187         timer_set_period(TIM1, 65535);
 188         timer_update_on_overflow(TIM1);
 189
 190         // IC1 will trigger on TI1 (TIM1_CH1) falling edge
 191         timer_ic_set_input(TIM1, TIM_IC1, TIM_IC_IN_TI1);
 192         // timer_ic_set_filter(TIM1, TIM_IC1, TIM_IC_OFF);
 193         timer_set_oc_polarity_low(TIM1, TIM_OC1);       // OC functions affect IC, too
 194
 195         // IC2 will trigger on TI1 (TIM1_CH1) rising edge
 196         timer_ic_set_input(TIM1, TIM_IC2, TIM_IC_IN_TI1);
 197         timer_set_oc_polarity_high(TIM1, TIM_OC2);
 198
 199         // OC3 will trigger on a break longer than 50 ms
 200         timer_set_oc_mode(TIM1, TIM_OC3, TIM_OCM_ACTIVE);
 201         timer_set_oc_value(TIM1, TIM_OC3, 30000);
 202
 203         // Program slave controller to reset the timer on IC1
 204         timer_slave_set_trigger(TIM1, TIM_SMCR_TS_TI1FP1);
 205         timer_slave_set_mode(TIM1, TIM_SMCR_SMS_RM);
 206
 207         // Request interrupts
 208         timer_enable_irq(TIM1, TIM_DIER_CC1IE | TIM_DIER_CC2IE | TIM_DIER_CC3IE);
 209         nvic_enable_irq(NVIC_TIM1_CC_IRQ);
 210
 211         // Enable ICs and OCs
 212         timer_enable_oc_output(TIM1, TIM_OC1);
 213         timer_enable_oc_output(TIM1, TIM_OC2);
 214         timer_enable_oc_output(TIM1, TIM_OC3);
 215
 216         timer_enable_counter(TIM1);
 217 }
 218
 219 // Circular queue of pulse durations
 220 #define IR_MAX_PULSES 32
 221 static u32 ir_pulses[IR_MAX_PULSES];    // Top 16 bits = mark, bottom 16 bits = space
 222 static u16 ir_last_pulse;
 223 static uint ir_pulses_rx, ir_pulses_tx;
 224
 225 #define IR_INF 0xffff
 226
 227 #define IR_MARK(x) (uint)((x) >> 16)
 228 #define IR_SPACE(x) (uint)((x) & 0xffff)
 229
 230 static inline bool between(uint x, uint min, uint max)
 231 {
 232         return x >= min && x <= max;
 233 }
 234
 235 static void ir_record_pulse(uint mark, uint space)
 236 {
 237         uint i = ir_pulses_tx;
 238         ir_pulses_tx = (i + 1) % IR_MAX_PULSES;
 239         if (ir_pulses_tx != ir_pulses_rx) {
 240                 ir_pulses[i] = (mark << 16) | space;
 241         } else {
 242                 // Overflow detected
 243                 ir_pulses[i] = (IR_INF << 16) | IR_INF;
 244         }
 245 }
 246
 247 void tim1_cc_isr(void)
 248 {
 249         if (TIM_SR(TIM1) & TIM_SR_CC1IF) {
 250                 TIM_SR(TIM1) &= ~TIM_SR_CC1IF;
 251                 u16 now = TIM_CCR1(TIM1);
 252                 if (ir_last_pulse) {
 253                         ir_record_pulse(ir_last_pulse, now - ir_last_pulse);
 254                         ir_last_pulse = 0;
 255                 }
 256         }
 257         if (TIM_SR(TIM1) & TIM_SR_CC2IF) {
 258                 TIM_SR(TIM1) &= ~TIM_SR_CC2IF;
 259                 ir_last_pulse = TIM_CCR2(TIM1);
 260         }
 261         if (TIM_SR(TIM1) & TIM_SR_CC3IF) {
 262                 TIM_SR(TIM1) &= ~TIM_SR_CC3IF;
 263                 if (ir_last_pulse) {
 264                         ir_record_pulse(ir_last_pulse, IR_INF);
 265                         ir_last_pulse = 0;
 266                 }
 267         }
 268 }
 269
 270 static u32 ir_get_pulse(void)
 271 {
 272         u32 out = 0;
 273
 274         cm_disable_interrupts();
 275         if (ir_pulses_rx != ir_pulses_tx) {
 276                 out = ir_pulses[ir_pulses_rx];
 277                 ir_pulses_rx = (ir_pulses_rx + 1) % IR_MAX_PULSES;
 278         }
 279         cm_enable_interrupts();
 280         return out;
 281 }
 282
 283 // Decoder for Onkyo RC-748S
 284
 285 static u32 ir_blink_start;
 286
 287 static void ir_decode(void)
 288 {
 289         u32 pulse = ir_get_pulse();
 290         if (!pulse)
 291                 return;
 292
 293         uint mark = IR_MARK(pulse);
 294         uint space = IR_SPACE(pulse);
 295
 296 #ifdef IR_TEST
 297         debug_printf("IR: %d %d\n", mark, space);
 298         return;
 299 #endif
 300
 301         static u16 ir_bits;
 302         static u32 ir_code;
 303 #define IR_ERR 0xff
 304
 305         // debug_printf("IR(%d): %d %d\n", ir_bits, mark, space);
 306
 307         if (space == IR_INF) {
 308                 ir_bits = 0;
 309         } else if (ir_bits == IR_ERR) {
 310                 // Error state
 311         } else if (ir_bits == 0) {
 312                 // Start?
 313                 if (between(mark, 8900, 9200)) {
 314                         if (between(space, 4200, 4600)) {
 315                                 ir_bits = 1;
 316                                 ir_code = 0;
 317                         } else if (between(space, 2000, 2300)) {
 318                                 debug_printf("IR: => REP\n");
 319                                 ir_bits = IR_ERR;
 320                         }
 321                 }
 322         } else {
 323                 if (between(mark, 500, 700)) {
 324                         ir_bits++;
 325                         if (between(space, 400, 700)) {
 326                                 // 0
 327                         } else if (between(space, 1500, 1800)) {
 328                                 // 1
 329                                 ir_code |= 1U << (33 - ir_bits);
 330                         } else {
 331                                 ir_bits = IR_ERR;
 332                         }
 333                         if (ir_bits == 33) {
 334                                 debug_printf("IR: => %08x\n", (uint)ir_code);
 335                                 disp[3] |= 0x01;
 336                                 ir_blink_start = ms_ticks;
 337                                 display_update();
 338                                 ir_bits = IR_ERR;
 339                                 ep82_send(ir_code);
 340                         }
 341                 } else {
 342                         ir_bits = IR_ERR;
 343                 }
 344         }
 345 }
 346
 347 /*** USB ***/
 348
 349 static usbd_device *usbd_dev;
 350
 351 enum usb_string {
 352         STR_MANUFACTURER = 1,
 353         STR_PRODUCT,
 354         STR_SERIAL,
 355 };
 356
 357 static char usb_serial_number[13];
 358
 359 static const char *usb_strings[] = {
 360         "United Computer Wizards",
 361         "Workshop Clock",
 362         usb_serial_number,
 363 };
 364
 365 static const struct usb_device_descriptor device = {
 366         .bLength = USB_DT_DEVICE_SIZE,
 367         .bDescriptorType = USB_DT_DEVICE,
 368         .bcdUSB = 0x0200,
 369         .bDeviceClass = 0xFF,
 370         .bDeviceSubClass = 0,
 371         .bDeviceProtocol = 0,
 372         .bMaxPacketSize0 = 64,
 373         .idVendor = 0x4242,
 374         .idProduct = 0x000d,
 375         .bcdDevice = 0x0000,
 376         .iManufacturer = STR_MANUFACTURER,
 377         .iProduct = STR_PRODUCT,
 378         .iSerialNumber = STR_SERIAL,
 379         .bNumConfigurations = 1,
 380 };
 381
 382 static const struct usb_endpoint_descriptor endpoints[] = {{
 383         // Bulk end-point for sending values to the display
 384         .bLength = USB_DT_ENDPOINT_SIZE,
 385         .bDescriptorType = USB_DT_ENDPOINT,
 386         .bEndpointAddress = 0x01,
 387         .bmAttributes = USB_ENDPOINT_ATTR_BULK,
 388         .wMaxPacketSize = 64,
 389         .bInterval = 1,
 390 }, {
 391         // Bulk end-point for receiving remote control keys
 392         .bLength = USB_DT_ENDPOINT_SIZE,
 393         .bDescriptorType = USB_DT_ENDPOINT,
 394         .bEndpointAddress = 0x82,
 395         .bmAttributes = USB_ENDPOINT_ATTR_BULK,
 396         .wMaxPacketSize = 4,
 397         .bInterval = 1,
 398 }};
 399
 400 static const struct usb_interface_descriptor iface = {
 401         .bLength = USB_DT_INTERFACE_SIZE,
 402         .bDescriptorType = USB_DT_INTERFACE,
 403         .bInterfaceNumber = 0,
 404         .bAlternateSetting = 0,
 405         .bNumEndpoints = 2,
 406         .bInterfaceClass = 0xFF,
 407         .bInterfaceSubClass = 0,
 408         .bInterfaceProtocol = 0,
 409         .iInterface = 0,
 410         .endpoint = endpoints,
 411 };
 412
 413 static const struct usb_dfu_descriptor dfu_function = {
 414         .bLength = sizeof(struct usb_dfu_descriptor),
 415         .bDescriptorType = DFU_FUNCTIONAL,
 416         .bmAttributes = USB_DFU_CAN_DOWNLOAD | USB_DFU_WILL_DETACH,
 417         .wDetachTimeout = 255,
 418         .wTransferSize = 1024,
 419         .bcdDFUVersion = 0x0100,
 420 };
 421
 422 static const struct usb_interface_descriptor dfu_iface = {
 423         .bLength = USB_DT_INTERFACE_SIZE,
 424         .bDescriptorType = USB_DT_INTERFACE,
 425         .bInterfaceNumber = 1,
 426         .bAlternateSetting = 0,
 427         .bNumEndpoints = 0,
 428         .bInterfaceClass = 0xFE,
 429         .bInterfaceSubClass = 1,
 430         .bInterfaceProtocol = 1,
 431         .iInterface = 0,
 432
 433         .extra = &dfu_function,
 434         .extralen = sizeof(dfu_function),
 435 };
 436
 437 static const struct usb_interface ifaces[] = {{
 438         .num_altsetting = 1,
 439         .altsetting = &iface,
 440 }, {
 441         .num_altsetting = 1,
 442         .altsetting = &dfu_iface,
 443 }};
 444
 445 static const struct usb_config_descriptor config = {
 446         .bLength = USB_DT_CONFIGURATION_SIZE,
 447         .bDescriptorType = USB_DT_CONFIGURATION,
 448         .wTotalLength = 0,
 449         .bNumInterfaces = 2,
 450         .bConfigurationValue = 1,
 451         .iConfiguration = 0,
 452         .bmAttributes = 0x80,
 453         .bMaxPower = 50,        // multiplied by 2 mA
 454         .interface = ifaces,
 455 };
 456
 457 static bool usb_configured;
 458 static uint8_t usbd_control_buffer[64];
 459
 460 static bool usb_tx_in_flight;
 461 static byte ep82_tx_buffer[4];
 462
 463 static byte disp_alive;
 464
 465 static void dfu_detach_complete(usbd_device *dev UNUSED, struct usb_setup_data *req UNUSED)
 466 {
 467         // Reset to bootloader, which implements the rest of DFU
 468         debug_printf("Switching to DFU\n");
 469         debug_flush();
 470         scb_reset_core();
 471 }
 472
 473 static enum usbd_request_return_codes dfu_control_cb(usbd_device *dev UNUSED,
 474         struct usb_setup_data *req,
 475         uint8_t **buf UNUSED,
 476         uint16_t *len UNUSED,
 477         void (**complete)(usbd_device *dev, struct usb_setup_data *req))
 478 {
 479         if (req->bmRequestType != 0x21 || req->bRequest != DFU_DETACH)
 480                 return USBD_REQ_NOTSUPP;
 481
 482         *complete = dfu_detach_complete;
 483         return USBD_REQ_HANDLED;
 484 }
 485
 486 static void ep01_cb(usbd_device *dev, uint8_t ep UNUSED)
 487 {
 488         // We received a frame from the USB host
 489         byte buf[8];
 490         uint len = usbd_ep_read_packet(dev, 0x01, buf, 8);
 491         debug_printf("USB: Host sent %u bytes\n", len);
 492         if (len >= 5) {
 493                 for (uint i=0; i<4; i++) {
 494                         disp[i] &= 0x01;
 495                         if (buf[i] < 16)
 496                                 disp[i] |= disp_font[buf[i]];
 497                 }
 498                 disp[1] &= 0xfe;
 499                 if (buf[4])
 500                         disp[1] |= 0x01;
 501                 display_update();
 502                 disp_alive = 10;
 503         }
 504 }
 505
 506 static void ep82_send(u32 key_code)
 507 {
 508         if (!usb_configured)
 509                 return;
 510
 511         if (usb_tx_in_flight) {
 512                 debug_printf("USB: Send overrun!\n");
 513                 return;
 514         }
 515
 516         debug_printf("USB: Sending key to host\n");
 517         put_u32_be(ep82_tx_buffer, key_code);
 518         usbd_ep_write_packet(usbd_dev, 0x82, ep82_tx_buffer, 4);
 519         usb_tx_in_flight = true;
 520 }
 521
 522 static void ep82_cb(usbd_device *dev UNUSED, uint8_t ep UNUSED)
 523 {
 524         // We completed sending a frame to the USB host
 525         usb_tx_in_flight = false;
 526         debug_printf("USB: Key sending complete\n");
 527 }
 528
 529 static void set_config_cb(usbd_device *dev, uint16_t wValue UNUSED)
 530 {
 531         usbd_register_control_callback(
 532                 dev,
 533                 USB_REQ_TYPE_CLASS | USB_REQ_TYPE_INTERFACE,
 534                 USB_REQ_TYPE_TYPE | USB_REQ_TYPE_RECIPIENT,
 535                 dfu_control_cb);
 536         usbd_ep_setup(dev, 0x01, USB_ENDPOINT_ATTR_BULK, 64, ep01_cb);
 537         usbd_ep_setup(dev, 0x82, USB_ENDPOINT_ATTR_BULK, 4, ep82_cb);
 538         usb_configured = true;
 539         usb_tx_in_flight = false;
 540 }
 541
 542 static void reset_cb(void)
 543 {
 544         debug_printf("USB: Reset\n");
 545         usb_configured = false;
 546 }
 547
 548 static volatile bool usb_event_pending;
 549
 550 void usb_lp_can_rx0_isr(void)
 551 {
 552         /*
 553          *  We handle USB in the main loop to avoid race conditions between
 554          *  USB interrupts and other code. However, we need an interrupt to
 555          *  up the main loop from sleep.
 556          *
 557          *  We set up only the low-priority ISR, because high-priority ISR handles
 558          *  only double-buffered bulk transfers and isochronous transfers.
 559          */
 560         nvic_disable_irq(NVIC_USB_LP_CAN_RX0_IRQ);
 561         usb_event_pending = 1;
 562 }
 563
 564 static void usb_init(void)
 565 {
 566         // Simulate USB disconnect
 567         gpio_set_mode(GPIOA, GPIO_MODE_OUTPUT_50_MHZ, GPIO_CNF_OUTPUT_OPENDRAIN, GPIO11 | GPIO12);
 568         gpio_clear(GPIOA, GPIO11 | GPIO12);
 569         delay_ms(100);
 570
 571         usbd_dev = usbd_init(
 572                 &st_usbfs_v1_usb_driver,
 573                 &device,
 574                 &config,
 575                 usb_strings,
 576                 ARRAY_SIZE(usb_strings),
 577                 usbd_control_buffer,
 578                 sizeof(usbd_control_buffer)
 579         );
 580         usbd_register_reset_callback(usbd_dev, reset_cb);
 581         usbd_register_set_config_callback(usbd_dev, set_config_cb);
 582         usb_event_pending = 1;
 583 }
 584
 585 /*** Main ***/
 586
 587 int main(void)
 588 {
 589         clock_init();
 590         gpio_init();
 591         usart_init();
 592
 593         tick_init();
 594         desig_get_unique_id_as_dfu(usb_serial_number);
 595
 596         debug_printf("Hello, world!\n");
 597
 598         usb_init();
 599         display_init();
 600         ir_init();
 601
 602         u32 last_blink = 0;
 603
 604         for (;;) {
 605                 if (ms_ticks - last_blink >= 500) {
 606                         debug_led_toggle();
 607                         last_blink = ms_ticks;
 608                         if (disp_alive) {
 609                                 if (!--disp_alive) {
 610                                         disp[0] = (disp[0] & 0x01) | 0x10;
 611                                         disp[1] = (disp[1] & 0x01) | 0x10;
 612                                         disp[2] = (disp[2] & 0x01) | 0x10;
 613                                         disp[3] = (disp[3] & 0x01) | 0x10;
 614                                 }
 615                         }
 616                         display_update();
 617                 }
 618
 619                 if ((disp[3] & 0x01) && ms_ticks - ir_blink_start >= 100) {
 620                         disp[3] &= 0xfe;
 621                         display_update();
 622                 }
 623
 624                 ir_decode();
 625
 626                 if (usb_event_pending) {
 627                         usbd_poll(usbd_dev);
 628                         usb_event_pending = 0;
 629                         nvic_clear_pending_irq(NVIC_USB_LP_CAN_RX0_IRQ);
 630                         nvic_enable_irq(NVIC_USB_LP_CAN_RX0_IRQ);
 631                 }
 632
 633                 wait_for_interrupt();
 634         }
 635
 636         return 0;
 637 }