1 // SPDX-License-Identifier: GPL-2.0+ 2 /* 3 * Copyright (C) 2009 by Bart Hartgers (bart.hartgers+ark3116@gmail.com) 4 * Original version: 5 * Copyright (C) 2006 6 * Simon Schulz (ark3116_driver <at> auctionant.de) 7 * 8 * ark3116 9 * - implements a driver for the arkmicro ark3116 chipset (vendor=0x6547, 10 * productid=0x0232) (used in a datacable called KQ-U8A) 11 * 12 * Supports full modem status lines, break, hardware flow control. Does not 13 * support software flow control, since I do not know how to enable it in hw. 14 * 15 * This driver is a essentially new implementation. I initially dug 16 * into the old ark3116.c driver and suddenly realized the ark3116 is 17 * a 16450 with a USB interface glued to it. See comments at the 18 * bottom of this file. 19 */ 20 21 #include <linux/kernel.h> 22 #include <linux/ioctl.h> 23 #include <linux/tty.h> 24 #include <linux/slab.h> 25 #include <linux/tty_flip.h> 26 #include <linux/module.h> 27 #include <linux/usb.h> 28 #include <linux/usb/serial.h> 29 #include <linux/serial.h> 30 #include <linux/serial_reg.h> 31 #include <linux/uaccess.h> 32 #include <linux/mutex.h> 33 #include <linux/spinlock.h> 34 35 #define DRIVER_AUTHOR "Bart Hartgers <bart.hartgers+ark3116@gmail.com>" 36 #define DRIVER_DESC "USB ARK3116 serial/IrDA driver" 37 #define DRIVER_DEV_DESC "ARK3116 RS232/IrDA" 38 #define DRIVER_NAME "ark3116" 39 40 /* usb timeout of 1 second */ 41 #define ARK_TIMEOUT 1000 42 43 static const struct usb_device_id id_table[] = { 44 { USB_DEVICE(0x6547, 0x0232) }, 45 { USB_DEVICE(0x18ec, 0x3118) }, /* USB to IrDA adapter */ 46 { }, 47 }; 48 MODULE_DEVICE_TABLE(usb, id_table); 49 50 static int is_irda(struct usb_serial *serial) 51 { 52 struct usb_device *dev = serial->dev; 53 if (le16_to_cpu(dev->descriptor.idVendor) == 0x18ec && 54 le16_to_cpu(dev->descriptor.idProduct) == 0x3118) 55 return 1; 56 return 0; 57 } 58 59 struct ark3116_private { 60 int irda; /* 1 for irda device */ 61 62 /* protects hw register updates */ 63 struct mutex hw_lock; 64 65 int quot; /* baudrate divisor */ 66 __u32 lcr; /* line control register value */ 67 __u32 hcr; /* handshake control register (0x8) 68 * value */ 69 __u32 mcr; /* modem control register value */ 70 71 /* protects the status values below */ 72 spinlock_t status_lock; 73 __u32 msr; /* modem status register value */ 74 __u32 lsr; /* line status register value */ 75 }; 76 77 static int ark3116_write_reg(struct usb_serial *serial, 78 unsigned reg, __u8 val) 79 { 80 int result; 81 /* 0xfe 0x40 are magic values taken from original driver */ 82 result = usb_control_msg(serial->dev, 83 usb_sndctrlpipe(serial->dev, 0), 84 0xfe, 0x40, val, reg, 85 NULL, 0, ARK_TIMEOUT); 86 if (result) 87 return result; 88 89 return 0; 90 } 91 92 static int ark3116_read_reg(struct usb_serial *serial, 93 unsigned reg, unsigned char *buf) 94 { 95 int result; 96 /* 0xfe 0xc0 are magic values taken from original driver */ 97 result = usb_control_msg(serial->dev, 98 usb_rcvctrlpipe(serial->dev, 0), 99 0xfe, 0xc0, 0, reg, 100 buf, 1, ARK_TIMEOUT); 101 if (result < 1) { 102 dev_err(&serial->interface->dev, 103 "failed to read register %u: %d\n", 104 reg, result); 105 if (result >= 0) 106 result = -EIO; 107 108 return result; 109 } 110 111 return 0; 112 } 113 114 static inline int calc_divisor(int bps) 115 { 116 /* Original ark3116 made some exceptions in rounding here 117 * because windows did the same. Assume that is not really 118 * necessary. 119 * Crystal is 12MHz, probably because of USB, but we divide by 4? 120 */ 121 return (12000000 + 2*bps) / (4*bps); 122 } 123 124 static int ark3116_port_probe(struct usb_serial_port *port) 125 { 126 struct usb_serial *serial = port->serial; 127 struct ark3116_private *priv; 128 129 priv = kzalloc(sizeof(*priv), GFP_KERNEL); 130 if (!priv) 131 return -ENOMEM; 132 133 mutex_init(&priv->hw_lock); 134 spin_lock_init(&priv->status_lock); 135 136 priv->irda = is_irda(serial); 137 138 usb_set_serial_port_data(port, priv); 139 140 /* setup the hardware */ 141 ark3116_write_reg(serial, UART_IER, 0); 142 /* disable DMA */ 143 ark3116_write_reg(serial, UART_FCR, 0); 144 /* handshake control */ 145 priv->hcr = 0; 146 ark3116_write_reg(serial, 0x8 , 0); 147 /* modem control */ 148 priv->mcr = 0; 149 ark3116_write_reg(serial, UART_MCR, 0); 150 151 if (!(priv->irda)) { 152 ark3116_write_reg(serial, 0xb , 0); 153 } else { 154 ark3116_write_reg(serial, 0xb , 1); 155 ark3116_write_reg(serial, 0xc , 0); 156 ark3116_write_reg(serial, 0xd , 0x41); 157 ark3116_write_reg(serial, 0xa , 1); 158 } 159 160 /* setup baudrate */ 161 ark3116_write_reg(serial, UART_LCR, UART_LCR_DLAB); 162 163 /* setup for 9600 8N1 */ 164 priv->quot = calc_divisor(9600); 165 ark3116_write_reg(serial, UART_DLL, priv->quot & 0xff); 166 ark3116_write_reg(serial, UART_DLM, (priv->quot>>8) & 0xff); 167 168 priv->lcr = UART_LCR_WLEN8; 169 ark3116_write_reg(serial, UART_LCR, UART_LCR_WLEN8); 170 171 ark3116_write_reg(serial, 0xe, 0); 172 173 if (priv->irda) 174 ark3116_write_reg(serial, 0x9, 0); 175 176 dev_info(&port->dev, "using %s mode\n", priv->irda ? "IrDA" : "RS232"); 177 178 return 0; 179 } 180 181 static int ark3116_port_remove(struct usb_serial_port *port) 182 { 183 struct ark3116_private *priv = usb_get_serial_port_data(port); 184 185 /* device is closed, so URBs and DMA should be down */ 186 mutex_destroy(&priv->hw_lock); 187 kfree(priv); 188 189 return 0; 190 } 191 192 static void ark3116_set_termios(struct tty_struct *tty, 193 struct usb_serial_port *port, 194 struct ktermios *old_termios) 195 { 196 struct usb_serial *serial = port->serial; 197 struct ark3116_private *priv = usb_get_serial_port_data(port); 198 struct ktermios *termios = &tty->termios; 199 unsigned int cflag = termios->c_cflag; 200 int bps = tty_get_baud_rate(tty); 201 int quot; 202 __u8 lcr, hcr, eval; 203 204 /* set data bit count */ 205 switch (cflag & CSIZE) { 206 case CS5: 207 lcr = UART_LCR_WLEN5; 208 break; 209 case CS6: 210 lcr = UART_LCR_WLEN6; 211 break; 212 case CS7: 213 lcr = UART_LCR_WLEN7; 214 break; 215 default: 216 case CS8: 217 lcr = UART_LCR_WLEN8; 218 break; 219 } 220 if (cflag & CSTOPB) 221 lcr |= UART_LCR_STOP; 222 if (cflag & PARENB) 223 lcr |= UART_LCR_PARITY; 224 if (!(cflag & PARODD)) 225 lcr |= UART_LCR_EPAR; 226 #ifdef CMSPAR 227 if (cflag & CMSPAR) 228 lcr |= UART_LCR_SPAR; 229 #endif 230 /* handshake control */ 231 hcr = (cflag & CRTSCTS) ? 0x03 : 0x00; 232 233 /* calc baudrate */ 234 dev_dbg(&port->dev, "%s - setting bps to %d\n", __func__, bps); 235 eval = 0; 236 switch (bps) { 237 case 0: 238 quot = calc_divisor(9600); 239 break; 240 default: 241 if ((bps < 75) || (bps > 3000000)) 242 bps = 9600; 243 quot = calc_divisor(bps); 244 break; 245 case 460800: 246 eval = 1; 247 quot = calc_divisor(bps); 248 break; 249 case 921600: 250 eval = 2; 251 quot = calc_divisor(bps); 252 break; 253 } 254 255 /* Update state: synchronize */ 256 mutex_lock(&priv->hw_lock); 257 258 /* keep old LCR_SBC bit */ 259 lcr |= (priv->lcr & UART_LCR_SBC); 260 261 dev_dbg(&port->dev, "%s - setting hcr:0x%02x,lcr:0x%02x,quot:%d\n", 262 __func__, hcr, lcr, quot); 263 264 /* handshake control */ 265 if (priv->hcr != hcr) { 266 priv->hcr = hcr; 267 ark3116_write_reg(serial, 0x8, hcr); 268 } 269 270 /* baudrate */ 271 if (priv->quot != quot) { 272 priv->quot = quot; 273 priv->lcr = lcr; /* need to write lcr anyway */ 274 275 /* disable DMA since transmit/receive is 276 * shadowed by UART_DLL 277 */ 278 ark3116_write_reg(serial, UART_FCR, 0); 279 280 ark3116_write_reg(serial, UART_LCR, 281 lcr|UART_LCR_DLAB); 282 ark3116_write_reg(serial, UART_DLL, quot & 0xff); 283 ark3116_write_reg(serial, UART_DLM, (quot>>8) & 0xff); 284 285 /* restore lcr */ 286 ark3116_write_reg(serial, UART_LCR, lcr); 287 /* magic baudrate thingy: not sure what it does, 288 * but windows does this as well. 289 */ 290 ark3116_write_reg(serial, 0xe, eval); 291 292 /* enable DMA */ 293 ark3116_write_reg(serial, UART_FCR, UART_FCR_DMA_SELECT); 294 } else if (priv->lcr != lcr) { 295 priv->lcr = lcr; 296 ark3116_write_reg(serial, UART_LCR, lcr); 297 } 298 299 mutex_unlock(&priv->hw_lock); 300 301 /* check for software flow control */ 302 if (I_IXOFF(tty) || I_IXON(tty)) { 303 dev_warn(&port->dev, 304 "software flow control not implemented\n"); 305 } 306 307 /* Don't rewrite B0 */ 308 if (tty_termios_baud_rate(termios)) 309 tty_termios_encode_baud_rate(termios, bps, bps); 310 } 311 312 static void ark3116_close(struct usb_serial_port *port) 313 { 314 struct usb_serial *serial = port->serial; 315 316 /* disable DMA */ 317 ark3116_write_reg(serial, UART_FCR, 0); 318 319 /* deactivate interrupts */ 320 ark3116_write_reg(serial, UART_IER, 0); 321 322 usb_serial_generic_close(port); 323 324 usb_kill_urb(port->interrupt_in_urb); 325 } 326 327 static int ark3116_open(struct tty_struct *tty, struct usb_serial_port *port) 328 { 329 struct ark3116_private *priv = usb_get_serial_port_data(port); 330 struct usb_serial *serial = port->serial; 331 unsigned char *buf; 332 int result; 333 334 buf = kmalloc(1, GFP_KERNEL); 335 if (buf == NULL) 336 return -ENOMEM; 337 338 result = usb_serial_generic_open(tty, port); 339 if (result) { 340 dev_dbg(&port->dev, 341 "%s - usb_serial_generic_open failed: %d\n", 342 __func__, result); 343 goto err_free; 344 } 345 346 /* remove any data still left: also clears error state */ 347 ark3116_read_reg(serial, UART_RX, buf); 348 349 /* read modem status */ 350 result = ark3116_read_reg(serial, UART_MSR, buf); 351 if (result) 352 goto err_close; 353 priv->msr = *buf; 354 355 /* read line status */ 356 result = ark3116_read_reg(serial, UART_LSR, buf); 357 if (result) 358 goto err_close; 359 priv->lsr = *buf; 360 361 result = usb_submit_urb(port->interrupt_in_urb, GFP_KERNEL); 362 if (result) { 363 dev_err(&port->dev, "submit irq_in urb failed %d\n", 364 result); 365 goto err_close; 366 } 367 368 /* activate interrupts */ 369 ark3116_write_reg(port->serial, UART_IER, UART_IER_MSI|UART_IER_RLSI); 370 371 /* enable DMA */ 372 ark3116_write_reg(port->serial, UART_FCR, UART_FCR_DMA_SELECT); 373 374 /* setup termios */ 375 if (tty) 376 ark3116_set_termios(tty, port, NULL); 377 378 kfree(buf); 379 380 return 0; 381 382 err_close: 383 usb_serial_generic_close(port); 384 err_free: 385 kfree(buf); 386 387 return result; 388 } 389 390 static int ark3116_get_serial_info(struct tty_struct *tty, 391 struct serial_struct *ss) 392 { 393 struct usb_serial_port *port = tty->driver_data; 394 395 ss->type = PORT_16654; 396 ss->line = port->minor; 397 ss->port = port->port_number; 398 ss->baud_base = 460800; 399 return 0; 400 } 401 402 static int ark3116_tiocmget(struct tty_struct *tty) 403 { 404 struct usb_serial_port *port = tty->driver_data; 405 struct ark3116_private *priv = usb_get_serial_port_data(port); 406 __u32 status; 407 __u32 ctrl; 408 unsigned long flags; 409 410 mutex_lock(&priv->hw_lock); 411 ctrl = priv->mcr; 412 mutex_unlock(&priv->hw_lock); 413 414 spin_lock_irqsave(&priv->status_lock, flags); 415 status = priv->msr; 416 spin_unlock_irqrestore(&priv->status_lock, flags); 417 418 return (status & UART_MSR_DSR ? TIOCM_DSR : 0) | 419 (status & UART_MSR_CTS ? TIOCM_CTS : 0) | 420 (status & UART_MSR_RI ? TIOCM_RI : 0) | 421 (status & UART_MSR_DCD ? TIOCM_CD : 0) | 422 (ctrl & UART_MCR_DTR ? TIOCM_DTR : 0) | 423 (ctrl & UART_MCR_RTS ? TIOCM_RTS : 0) | 424 (ctrl & UART_MCR_OUT1 ? TIOCM_OUT1 : 0) | 425 (ctrl & UART_MCR_OUT2 ? TIOCM_OUT2 : 0); 426 } 427 428 static int ark3116_tiocmset(struct tty_struct *tty, 429 unsigned set, unsigned clr) 430 { 431 struct usb_serial_port *port = tty->driver_data; 432 struct ark3116_private *priv = usb_get_serial_port_data(port); 433 434 /* we need to take the mutex here, to make sure that the value 435 * in priv->mcr is actually the one that is in the hardware 436 */ 437 438 mutex_lock(&priv->hw_lock); 439 440 if (set & TIOCM_RTS) 441 priv->mcr |= UART_MCR_RTS; 442 if (set & TIOCM_DTR) 443 priv->mcr |= UART_MCR_DTR; 444 if (set & TIOCM_OUT1) 445 priv->mcr |= UART_MCR_OUT1; 446 if (set & TIOCM_OUT2) 447 priv->mcr |= UART_MCR_OUT2; 448 if (clr & TIOCM_RTS) 449 priv->mcr &= ~UART_MCR_RTS; 450 if (clr & TIOCM_DTR) 451 priv->mcr &= ~UART_MCR_DTR; 452 if (clr & TIOCM_OUT1) 453 priv->mcr &= ~UART_MCR_OUT1; 454 if (clr & TIOCM_OUT2) 455 priv->mcr &= ~UART_MCR_OUT2; 456 457 ark3116_write_reg(port->serial, UART_MCR, priv->mcr); 458 459 mutex_unlock(&priv->hw_lock); 460 461 return 0; 462 } 463 464 static void ark3116_break_ctl(struct tty_struct *tty, int break_state) 465 { 466 struct usb_serial_port *port = tty->driver_data; 467 struct ark3116_private *priv = usb_get_serial_port_data(port); 468 469 /* LCR is also used for other things: protect access */ 470 mutex_lock(&priv->hw_lock); 471 472 if (break_state) 473 priv->lcr |= UART_LCR_SBC; 474 else 475 priv->lcr &= ~UART_LCR_SBC; 476 477 ark3116_write_reg(port->serial, UART_LCR, priv->lcr); 478 479 mutex_unlock(&priv->hw_lock); 480 } 481 482 static void ark3116_update_msr(struct usb_serial_port *port, __u8 msr) 483 { 484 struct ark3116_private *priv = usb_get_serial_port_data(port); 485 unsigned long flags; 486 487 spin_lock_irqsave(&priv->status_lock, flags); 488 priv->msr = msr; 489 spin_unlock_irqrestore(&priv->status_lock, flags); 490 491 if (msr & UART_MSR_ANY_DELTA) { 492 /* update input line counters */ 493 if (msr & UART_MSR_DCTS) 494 port->icount.cts++; 495 if (msr & UART_MSR_DDSR) 496 port->icount.dsr++; 497 if (msr & UART_MSR_DDCD) 498 port->icount.dcd++; 499 if (msr & UART_MSR_TERI) 500 port->icount.rng++; 501 wake_up_interruptible(&port->port.delta_msr_wait); 502 } 503 } 504 505 static void ark3116_update_lsr(struct usb_serial_port *port, __u8 lsr) 506 { 507 struct ark3116_private *priv = usb_get_serial_port_data(port); 508 unsigned long flags; 509 510 spin_lock_irqsave(&priv->status_lock, flags); 511 /* combine bits */ 512 priv->lsr |= lsr; 513 spin_unlock_irqrestore(&priv->status_lock, flags); 514 515 if (lsr&UART_LSR_BRK_ERROR_BITS) { 516 if (lsr & UART_LSR_BI) 517 port->icount.brk++; 518 if (lsr & UART_LSR_FE) 519 port->icount.frame++; 520 if (lsr & UART_LSR_PE) 521 port->icount.parity++; 522 if (lsr & UART_LSR_OE) 523 port->icount.overrun++; 524 } 525 } 526 527 static void ark3116_read_int_callback(struct urb *urb) 528 { 529 struct usb_serial_port *port = urb->context; 530 int status = urb->status; 531 const __u8 *data = urb->transfer_buffer; 532 int result; 533 534 switch (status) { 535 case -ECONNRESET: 536 case -ENOENT: 537 case -ESHUTDOWN: 538 /* this urb is terminated, clean up */ 539 dev_dbg(&port->dev, "%s - urb shutting down with status: %d\n", 540 __func__, status); 541 return; 542 default: 543 dev_dbg(&port->dev, "%s - nonzero urb status received: %d\n", 544 __func__, status); 545 break; 546 case 0: /* success */ 547 /* discovered this by trail and error... */ 548 if ((urb->actual_length == 4) && (data[0] == 0xe8)) { 549 const __u8 id = data[1]&UART_IIR_ID; 550 dev_dbg(&port->dev, "%s: iir=%02x\n", __func__, data[1]); 551 if (id == UART_IIR_MSI) { 552 dev_dbg(&port->dev, "%s: msr=%02x\n", 553 __func__, data[3]); 554 ark3116_update_msr(port, data[3]); 555 break; 556 } else if (id == UART_IIR_RLSI) { 557 dev_dbg(&port->dev, "%s: lsr=%02x\n", 558 __func__, data[2]); 559 ark3116_update_lsr(port, data[2]); 560 break; 561 } 562 } 563 /* 564 * Not sure what this data meant... 565 */ 566 usb_serial_debug_data(&port->dev, __func__, 567 urb->actual_length, 568 urb->transfer_buffer); 569 break; 570 } 571 572 result = usb_submit_urb(urb, GFP_ATOMIC); 573 if (result) 574 dev_err(&port->dev, "failed to resubmit interrupt urb: %d\n", 575 result); 576 } 577 578 579 /* Data comes in via the bulk (data) URB, errors/interrupts via the int URB. 580 * This means that we cannot be sure which data byte has an associated error 581 * condition, so we report an error for all data in the next bulk read. 582 * 583 * Actually, there might even be a window between the bulk data leaving the 584 * ark and reading/resetting the lsr in the read_bulk_callback where an 585 * interrupt for the next data block could come in. 586 * Without somekind of ordering on the ark, we would have to report the 587 * error for the next block of data as well... 588 * For now, let's pretend this can't happen. 589 */ 590 static void ark3116_process_read_urb(struct urb *urb) 591 { 592 struct usb_serial_port *port = urb->context; 593 struct ark3116_private *priv = usb_get_serial_port_data(port); 594 unsigned char *data = urb->transfer_buffer; 595 char tty_flag = TTY_NORMAL; 596 unsigned long flags; 597 __u32 lsr; 598 599 /* update line status */ 600 spin_lock_irqsave(&priv->status_lock, flags); 601 lsr = priv->lsr; 602 priv->lsr &= ~UART_LSR_BRK_ERROR_BITS; 603 spin_unlock_irqrestore(&priv->status_lock, flags); 604 605 if (!urb->actual_length) 606 return; 607 608 if (lsr & UART_LSR_BRK_ERROR_BITS) { 609 if (lsr & UART_LSR_BI) 610 tty_flag = TTY_BREAK; 611 else if (lsr & UART_LSR_PE) 612 tty_flag = TTY_PARITY; 613 else if (lsr & UART_LSR_FE) 614 tty_flag = TTY_FRAME; 615 616 /* overrun is special, not associated with a char */ 617 if (lsr & UART_LSR_OE) 618 tty_insert_flip_char(&port->port, 0, TTY_OVERRUN); 619 } 620 tty_insert_flip_string_fixed_flag(&port->port, data, tty_flag, 621 urb->actual_length); 622 tty_flip_buffer_push(&port->port); 623 } 624 625 static struct usb_serial_driver ark3116_device = { 626 .driver = { 627 .owner = THIS_MODULE, 628 .name = "ark3116", 629 }, 630 .id_table = id_table, 631 .num_ports = 1, 632 .num_bulk_in = 1, 633 .num_bulk_out = 1, 634 .num_interrupt_in = 1, 635 .port_probe = ark3116_port_probe, 636 .port_remove = ark3116_port_remove, 637 .set_termios = ark3116_set_termios, 638 .get_serial = ark3116_get_serial_info, 639 .tiocmget = ark3116_tiocmget, 640 .tiocmset = ark3116_tiocmset, 641 .tiocmiwait = usb_serial_generic_tiocmiwait, 642 .get_icount = usb_serial_generic_get_icount, 643 .open = ark3116_open, 644 .close = ark3116_close, 645 .break_ctl = ark3116_break_ctl, 646 .read_int_callback = ark3116_read_int_callback, 647 .process_read_urb = ark3116_process_read_urb, 648 }; 649 650 static struct usb_serial_driver * const serial_drivers[] = { 651 &ark3116_device, NULL 652 }; 653 654 module_usb_serial_driver(serial_drivers, id_table); 655 656 MODULE_LICENSE("GPL"); 657 658 MODULE_AUTHOR(DRIVER_AUTHOR); 659 MODULE_DESCRIPTION(DRIVER_DESC); 660 661 /* 662 * The following describes what I learned from studying the old 663 * ark3116.c driver, disassembling the windows driver, and some lucky 664 * guesses. Since I do not have any datasheet or other 665 * documentation, inaccuracies are almost guaranteed. 666 * 667 * Some specs for the ARK3116 can be found here: 668 * http://web.archive.org/web/20060318000438/ 669 * www.arkmicro.com/en/products/view.php?id=10 670 * On that page, 2 GPIO pins are mentioned: I assume these are the 671 * OUT1 and OUT2 pins of the UART, so I added support for those 672 * through the MCR. Since the pins are not available on my hardware, 673 * I could not verify this. 674 * Also, it states there is "on-chip hardware flow control". I have 675 * discovered how to enable that. Unfortunately, I do not know how to 676 * enable XON/XOFF (software) flow control, which would need support 677 * from the chip as well to work. Because of the wording on the web 678 * page there is a real possibility the chip simply does not support 679 * software flow control. 680 * 681 * I got my ark3116 as part of a mobile phone adapter cable. On the 682 * PCB, the following numbered contacts are present: 683 * 684 * 1:- +5V 685 * 2:o DTR 686 * 3:i RX 687 * 4:i DCD 688 * 5:o RTS 689 * 6:o TX 690 * 7:i RI 691 * 8:i DSR 692 * 10:- 0V 693 * 11:i CTS 694 * 695 * On my chip, all signals seem to be 3.3V, but 5V tolerant. But that 696 * may be different for the one you have ;-). 697 * 698 * The windows driver limits the registers to 0-F, so I assume there 699 * are actually 16 present on the device. 700 * 701 * On an UART interrupt, 4 bytes of data come in on the interrupt 702 * endpoint. The bytes are 0xe8 IIR LSR MSR. 703 * 704 * The baudrate seems to be generated from the 12MHz crystal, using 705 * 4-times subsampling. So quot=12e6/(4*baud). Also see description 706 * of register E. 707 * 708 * Registers 0-7: 709 * These seem to be the same as for a regular 16450. The FCR is set 710 * to UART_FCR_DMA_SELECT (0x8), I guess to enable transfers between 711 * the UART and the USB bridge/DMA engine. 712 * 713 * Register 8: 714 * By trial and error, I found out that bit 0 enables hardware CTS, 715 * stopping TX when CTS is +5V. Bit 1 does the same for RTS, making 716 * RTS +5V when the 3116 cannot transfer the data to the USB bus 717 * (verified by disabling the reading URB). Note that as far as I can 718 * tell, the windows driver does NOT use this, so there might be some 719 * hardware bug or something. 720 * 721 * According to a patch provided here 722 * (http://lkml.org/lkml/2009/7/26/56), the ARK3116 can also be used 723 * as an IrDA dongle. Since I do not have such a thing, I could not 724 * investigate that aspect. However, I can speculate ;-). 725 * 726 * - IrDA encodes data differently than RS232. Most likely, one of 727 * the bits in registers 9..E enables the IR ENDEC (encoder/decoder). 728 * - Depending on the IR transceiver, the input and output need to be 729 * inverted, so there are probably bits for that as well. 730 * - IrDA is half-duplex, so there should be a bit for selecting that. 731 * 732 * This still leaves at least two registers unaccounted for. Perhaps 733 * The chip can do XON/XOFF or CRC in HW? 734 * 735 * Register 9: 736 * Set to 0x00 for IrDA, when the baudrate is initialised. 737 * 738 * Register A: 739 * Set to 0x01 for IrDA, at init. 740 * 741 * Register B: 742 * Set to 0x01 for IrDA, 0x00 for RS232, at init. 743 * 744 * Register C: 745 * Set to 00 for IrDA, at init. 746 * 747 * Register D: 748 * Set to 0x41 for IrDA, at init. 749 * 750 * Register E: 751 * Somekind of baudrate override. The windows driver seems to set 752 * this to 0x00 for normal baudrates, 0x01 for 460800, 0x02 for 921600. 753 * Since 460800 and 921600 cannot be obtained by dividing 3MHz by an integer, 754 * it could be somekind of subdivisor thingy. 755 * However,it does not seem to do anything: selecting 921600 (divisor 3, 756 * reg E=2), still gets 1 MHz. I also checked if registers 9, C or F would 757 * work, but they don't. 758 * 759 * Register F: unknown 760 */ 761