linux/drivers/usb/serial/ftdi_sio.h
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   1/*
   2 * Driver definitions for the FTDI USB Single Port Serial Converter -
   3 * known as FTDI_SIO (Serial Input/Output application of the chipset)
   4 *
   5 * For USB vendor/product IDs (VID/PID), please see ftdi_sio_ids.h
   6 *
   7 *
   8 * The example I have is known as the USC-1000 which is available from
   9 * http://www.dse.co.nz - cat no XH4214 It looks similar to this:
  10 * http://www.dansdata.com/usbser.htm but I can't be sure There are other
  11 * USC-1000s which don't look like my device though so beware!
  12 *
  13 * The device is based on the FTDI FT8U100AX chip. It has a DB25 on one side,
  14 * USB on the other.
  15 *
  16 * Thanx to FTDI (http://www.ftdichip.com) for so kindly providing details
  17 * of the protocol required to talk to the device and ongoing assistence
  18 * during development.
  19 *
  20 * Bill Ryder - bryder@sgi.com formerly of Silicon Graphics, Inc.- wrote the
  21 * FTDI_SIO implementation.
  22 *
  23 */
  24
  25/* Commands */
  26#define FTDI_SIO_RESET                  0 /* Reset the port */
  27#define FTDI_SIO_MODEM_CTRL             1 /* Set the modem control register */
  28#define FTDI_SIO_SET_FLOW_CTRL          2 /* Set flow control register */
  29#define FTDI_SIO_SET_BAUD_RATE          3 /* Set baud rate */
  30#define FTDI_SIO_SET_DATA               4 /* Set the data characteristics of
  31                                             the port */
  32#define FTDI_SIO_GET_MODEM_STATUS       5 /* Retrieve current value of modem
  33                                             status register */
  34#define FTDI_SIO_SET_EVENT_CHAR         6 /* Set the event character */
  35#define FTDI_SIO_SET_ERROR_CHAR         7 /* Set the error character */
  36#define FTDI_SIO_SET_LATENCY_TIMER      9 /* Set the latency timer */
  37#define FTDI_SIO_GET_LATENCY_TIMER      10 /* Get the latency timer */
  38
  39/* Interface indices for FT2232, FT2232H and FT4232H devices */
  40#define INTERFACE_A             1
  41#define INTERFACE_B             2
  42#define INTERFACE_C             3
  43#define INTERFACE_D             4
  44
  45
  46/*
  47 *   BmRequestType:  1100 0000b
  48 *   bRequest:       FTDI_E2_READ
  49 *   wValue:         0
  50 *   wIndex:         Address of word to read
  51 *   wLength:        2
  52 *   Data:           Will return a word of data from E2Address
  53 *
  54 */
  55
  56/* Port Identifier Table */
  57#define PIT_DEFAULT             0 /* SIOA */
  58#define PIT_SIOA                1 /* SIOA */
  59/* The device this driver is tested with one has only one port */
  60#define PIT_SIOB                2 /* SIOB */
  61#define PIT_PARALLEL            3 /* Parallel */
  62
  63/* FTDI_SIO_RESET */
  64#define FTDI_SIO_RESET_REQUEST FTDI_SIO_RESET
  65#define FTDI_SIO_RESET_REQUEST_TYPE 0x40
  66#define FTDI_SIO_RESET_SIO 0
  67#define FTDI_SIO_RESET_PURGE_RX 1
  68#define FTDI_SIO_RESET_PURGE_TX 2
  69
  70/*
  71 * BmRequestType:  0100 0000B
  72 * bRequest:       FTDI_SIO_RESET
  73 * wValue:         Control Value
  74 *                   0 = Reset SIO
  75 *                   1 = Purge RX buffer
  76 *                   2 = Purge TX buffer
  77 * wIndex:         Port
  78 * wLength:        0
  79 * Data:           None
  80 *
  81 * The Reset SIO command has this effect:
  82 *
  83 *    Sets flow control set to 'none'
  84 *    Event char = $0D
  85 *    Event trigger = disabled
  86 *    Purge RX buffer
  87 *    Purge TX buffer
  88 *    Clear DTR
  89 *    Clear RTS
  90 *    baud and data format not reset
  91 *
  92 * The Purge RX and TX buffer commands affect nothing except the buffers
  93 *
  94   */
  95
  96/* FTDI_SIO_SET_BAUDRATE */
  97#define FTDI_SIO_SET_BAUDRATE_REQUEST_TYPE 0x40
  98#define FTDI_SIO_SET_BAUDRATE_REQUEST 3
  99
 100/*
 101 * BmRequestType:  0100 0000B
 102 * bRequest:       FTDI_SIO_SET_BAUDRATE
 103 * wValue:         BaudDivisor value - see below
 104 * wIndex:         Port
 105 * wLength:        0
 106 * Data:           None
 107 * The BaudDivisor values are calculated as follows:
 108 * - BaseClock is either 12000000 or 48000000 depending on the device.
 109 *   FIXME: I wish I knew how to detect old chips to select proper base clock!
 110 * - BaudDivisor is a fixed point number encoded in a funny way.
 111 *   (--WRONG WAY OF THINKING--)
 112 *   BaudDivisor is a fixed point number encoded with following bit weighs:
 113 *   (-2)(-1)(13..0). It is a radical with a denominator of 4, so values
 114 *   end with 0.0 (00...), 0.25 (10...), 0.5 (01...), and 0.75 (11...).
 115 *   (--THE REALITY--)
 116 *   The both-bits-set has quite different meaning from 0.75 - the chip
 117 *   designers have decided it to mean 0.125 instead of 0.75.
 118 *   This info looked up in FTDI application note "FT8U232 DEVICES \ Data Rates
 119 *   and Flow Control Consideration for USB to RS232".
 120 * - BaudDivisor = (BaseClock / 16) / BaudRate, where the (=) operation should
 121 *   automagically re-encode the resulting value to take fractions into
 122 *   consideration.
 123 * As all values are integers, some bit twiddling is in order:
 124 *   BaudDivisor = (BaseClock / 16 / BaudRate) |
 125 *   (((BaseClock / 2 / BaudRate) & 4) ? 0x4000    // 0.5
 126 *    : ((BaseClock / 2 / BaudRate) & 2) ? 0x8000  // 0.25
 127 *    : ((BaseClock / 2 / BaudRate) & 1) ? 0xc000  // 0.125
 128 *    : 0)
 129 *
 130 * For the FT232BM, a 17th divisor bit was introduced to encode the multiples
 131 * of 0.125 missing from the FT8U232AM.  Bits 16 to 14 are coded as follows
 132 * (the first four codes are the same as for the FT8U232AM, where bit 16 is
 133 * always 0):
 134 *   000 - add .000 to divisor
 135 *   001 - add .500 to divisor
 136 *   010 - add .250 to divisor
 137 *   011 - add .125 to divisor
 138 *   100 - add .375 to divisor
 139 *   101 - add .625 to divisor
 140 *   110 - add .750 to divisor
 141 *   111 - add .875 to divisor
 142 * Bits 15 to 0 of the 17-bit divisor are placed in the urb value.  Bit 16 is
 143 * placed in bit 0 of the urb index.
 144 *
 145 * Note that there are a couple of special cases to support the highest baud
 146 * rates.  If the calculated divisor value is 1, this needs to be replaced with
 147 * 0.  Additionally for the FT232BM, if the calculated divisor value is 0x4001
 148 * (1.5), this needs to be replaced with 0x0001 (1) (but this divisor value is
 149 * not supported by the FT8U232AM).
 150 */
 151
 152enum ftdi_chip_type {
 153        SIO = 1,
 154        FT8U232AM = 2,
 155        FT232BM = 3,
 156        FT2232C = 4,
 157        FT232RL = 5,
 158        FT2232H = 6,
 159        FT4232H = 7,
 160        FT232H  = 8
 161};
 162
 163enum ftdi_sio_baudrate {
 164        ftdi_sio_b300 = 0,
 165        ftdi_sio_b600 = 1,
 166        ftdi_sio_b1200 = 2,
 167        ftdi_sio_b2400 = 3,
 168        ftdi_sio_b4800 = 4,
 169        ftdi_sio_b9600 = 5,
 170        ftdi_sio_b19200 = 6,
 171        ftdi_sio_b38400 = 7,
 172        ftdi_sio_b57600 = 8,
 173        ftdi_sio_b115200 = 9
 174};
 175
 176/*
 177 * The ftdi_8U232AM_xxMHz_byyy constants have been removed. The encoded divisor
 178 * values are calculated internally.
 179 */
 180#define FTDI_SIO_SET_DATA_REQUEST       FTDI_SIO_SET_DATA
 181#define FTDI_SIO_SET_DATA_REQUEST_TYPE  0x40
 182#define FTDI_SIO_SET_DATA_PARITY_NONE   (0x0 << 8)
 183#define FTDI_SIO_SET_DATA_PARITY_ODD    (0x1 << 8)
 184#define FTDI_SIO_SET_DATA_PARITY_EVEN   (0x2 << 8)
 185#define FTDI_SIO_SET_DATA_PARITY_MARK   (0x3 << 8)
 186#define FTDI_SIO_SET_DATA_PARITY_SPACE  (0x4 << 8)
 187#define FTDI_SIO_SET_DATA_STOP_BITS_1   (0x0 << 11)
 188#define FTDI_SIO_SET_DATA_STOP_BITS_15  (0x1 << 11)
 189#define FTDI_SIO_SET_DATA_STOP_BITS_2   (0x2 << 11)
 190#define FTDI_SIO_SET_BREAK              (0x1 << 14)
 191/* FTDI_SIO_SET_DATA */
 192
 193/*
 194 * BmRequestType:  0100 0000B
 195 * bRequest:       FTDI_SIO_SET_DATA
 196 * wValue:         Data characteristics (see below)
 197 * wIndex:         Port
 198 * wLength:        0
 199 * Data:           No
 200 *
 201 * Data characteristics
 202 *
 203 *   B0..7   Number of data bits
 204 *   B8..10  Parity
 205 *           0 = None
 206 *           1 = Odd
 207 *           2 = Even
 208 *           3 = Mark
 209 *           4 = Space
 210 *   B11..13 Stop Bits
 211 *           0 = 1
 212 *           1 = 1.5
 213 *           2 = 2
 214 *   B14
 215 *           1 = TX ON (break)
 216 *           0 = TX OFF (normal state)
 217 *   B15 Reserved
 218 *
 219 */
 220
 221
 222
 223/* FTDI_SIO_MODEM_CTRL */
 224#define FTDI_SIO_SET_MODEM_CTRL_REQUEST_TYPE 0x40
 225#define FTDI_SIO_SET_MODEM_CTRL_REQUEST FTDI_SIO_MODEM_CTRL
 226
 227/*
 228 * BmRequestType:   0100 0000B
 229 * bRequest:        FTDI_SIO_MODEM_CTRL
 230 * wValue:          ControlValue (see below)
 231 * wIndex:          Port
 232 * wLength:         0
 233 * Data:            None
 234 *
 235 * NOTE: If the device is in RTS/CTS flow control, the RTS set by this
 236 * command will be IGNORED without an error being returned
 237 * Also - you can not set DTR and RTS with one control message
 238 */
 239
 240#define FTDI_SIO_SET_DTR_MASK 0x1
 241#define FTDI_SIO_SET_DTR_HIGH (1 | (FTDI_SIO_SET_DTR_MASK  << 8))
 242#define FTDI_SIO_SET_DTR_LOW  (0 | (FTDI_SIO_SET_DTR_MASK  << 8))
 243#define FTDI_SIO_SET_RTS_MASK 0x2
 244#define FTDI_SIO_SET_RTS_HIGH (2 | (FTDI_SIO_SET_RTS_MASK << 8))
 245#define FTDI_SIO_SET_RTS_LOW (0 | (FTDI_SIO_SET_RTS_MASK << 8))
 246
 247/*
 248 * ControlValue
 249 * B0    DTR state
 250 *          0 = reset
 251 *          1 = set
 252 * B1    RTS state
 253 *          0 = reset
 254 *          1 = set
 255 * B2..7 Reserved
 256 * B8    DTR state enable
 257 *          0 = ignore
 258 *          1 = use DTR state
 259 * B9    RTS state enable
 260 *          0 = ignore
 261 *          1 = use RTS state
 262 * B10..15 Reserved
 263 */
 264
 265/* FTDI_SIO_SET_FLOW_CTRL */
 266#define FTDI_SIO_SET_FLOW_CTRL_REQUEST_TYPE 0x40
 267#define FTDI_SIO_SET_FLOW_CTRL_REQUEST FTDI_SIO_SET_FLOW_CTRL
 268#define FTDI_SIO_DISABLE_FLOW_CTRL 0x0
 269#define FTDI_SIO_RTS_CTS_HS (0x1 << 8)
 270#define FTDI_SIO_DTR_DSR_HS (0x2 << 8)
 271#define FTDI_SIO_XON_XOFF_HS (0x4 << 8)
 272/*
 273 *   BmRequestType:  0100 0000b
 274 *   bRequest:       FTDI_SIO_SET_FLOW_CTRL
 275 *   wValue:         Xoff/Xon
 276 *   wIndex:         Protocol/Port - hIndex is protocol / lIndex is port
 277 *   wLength:        0
 278 *   Data:           None
 279 *
 280 * hIndex protocol is:
 281 *   B0 Output handshaking using RTS/CTS
 282 *       0 = disabled
 283 *       1 = enabled
 284 *   B1 Output handshaking using DTR/DSR
 285 *       0 = disabled
 286 *       1 = enabled
 287 *   B2 Xon/Xoff handshaking
 288 *       0 = disabled
 289 *       1 = enabled
 290 *
 291 * A value of zero in the hIndex field disables handshaking
 292 *
 293 * If Xon/Xoff handshaking is specified, the hValue field should contain the
 294 * XOFF character and the lValue field contains the XON character.
 295 */
 296
 297/*
 298 * FTDI_SIO_GET_LATENCY_TIMER
 299 *
 300 * Set the timeout interval. The FTDI collects data from the slave
 301 * device, transmitting it to the host when either A) 62 bytes are
 302 * received, or B) the timeout interval has elapsed and the buffer
 303 * contains at least 1 byte.  Setting this value to a small number
 304 * can dramatically improve performance for applications which send
 305 * small packets, since the default value is 16ms.
 306 */
 307#define  FTDI_SIO_GET_LATENCY_TIMER_REQUEST FTDI_SIO_GET_LATENCY_TIMER
 308#define  FTDI_SIO_GET_LATENCY_TIMER_REQUEST_TYPE 0xC0
 309
 310/*
 311 *  BmRequestType:   1100 0000b
 312 *  bRequest:        FTDI_SIO_GET_LATENCY_TIMER
 313 *  wValue:          0
 314 *  wIndex:          Port
 315 *  wLength:         0
 316 *  Data:            latency (on return)
 317 */
 318
 319/*
 320 * FTDI_SIO_SET_LATENCY_TIMER
 321 *
 322 * Set the timeout interval. The FTDI collects data from the slave
 323 * device, transmitting it to the host when either A) 62 bytes are
 324 * received, or B) the timeout interval has elapsed and the buffer
 325 * contains at least 1 byte.  Setting this value to a small number
 326 * can dramatically improve performance for applications which send
 327 * small packets, since the default value is 16ms.
 328 */
 329#define  FTDI_SIO_SET_LATENCY_TIMER_REQUEST FTDI_SIO_SET_LATENCY_TIMER
 330#define  FTDI_SIO_SET_LATENCY_TIMER_REQUEST_TYPE 0x40
 331
 332/*
 333 *  BmRequestType:   0100 0000b
 334 *  bRequest:        FTDI_SIO_SET_LATENCY_TIMER
 335 *  wValue:          Latency (milliseconds)
 336 *  wIndex:          Port
 337 *  wLength:         0
 338 *  Data:            None
 339 *
 340 * wValue:
 341 *   B0..7   Latency timer
 342 *   B8..15  0
 343 *
 344 */
 345
 346/*
 347 * FTDI_SIO_SET_EVENT_CHAR
 348 *
 349 * Set the special event character for the specified communications port.
 350 * If the device sees this character it will immediately return the
 351 * data read so far - rather than wait 40ms or until 62 bytes are read
 352 * which is what normally happens.
 353 */
 354
 355
 356#define  FTDI_SIO_SET_EVENT_CHAR_REQUEST FTDI_SIO_SET_EVENT_CHAR
 357#define  FTDI_SIO_SET_EVENT_CHAR_REQUEST_TYPE 0x40
 358
 359
 360/*
 361 *  BmRequestType:   0100 0000b
 362 *  bRequest:        FTDI_SIO_SET_EVENT_CHAR
 363 *  wValue:          EventChar
 364 *  wIndex:          Port
 365 *  wLength:         0
 366 *  Data:            None
 367 *
 368 * wValue:
 369 *   B0..7   Event Character
 370 *   B8      Event Character Processing
 371 *             0 = disabled
 372 *             1 = enabled
 373 *   B9..15  Reserved
 374 *
 375 */
 376
 377/* FTDI_SIO_SET_ERROR_CHAR */
 378
 379/*
 380 * Set the parity error replacement character for the specified communications
 381 * port
 382 */
 383
 384/*
 385 *  BmRequestType:  0100 0000b
 386 *  bRequest:       FTDI_SIO_SET_EVENT_CHAR
 387 *  wValue:         Error Char
 388 *  wIndex:         Port
 389 *  wLength:        0
 390 *  Data:           None
 391 *
 392 *Error Char
 393 *  B0..7  Error Character
 394 *  B8     Error Character Processing
 395 *           0 = disabled
 396 *           1 = enabled
 397 *  B9..15 Reserved
 398 *
 399 */
 400
 401/* FTDI_SIO_GET_MODEM_STATUS */
 402/* Retrieve the current value of the modem status register */
 403
 404#define FTDI_SIO_GET_MODEM_STATUS_REQUEST_TYPE 0xc0
 405#define FTDI_SIO_GET_MODEM_STATUS_REQUEST FTDI_SIO_GET_MODEM_STATUS
 406#define FTDI_SIO_CTS_MASK 0x10
 407#define FTDI_SIO_DSR_MASK 0x20
 408#define FTDI_SIO_RI_MASK  0x40
 409#define FTDI_SIO_RLSD_MASK 0x80
 410/*
 411 *   BmRequestType:   1100 0000b
 412 *   bRequest:        FTDI_SIO_GET_MODEM_STATUS
 413 *   wValue:          zero
 414 *   wIndex:          Port
 415 *   wLength:         1
 416 *   Data:            Status
 417 *
 418 * One byte of data is returned
 419 * B0..3 0
 420 * B4    CTS
 421 *         0 = inactive
 422 *         1 = active
 423 * B5    DSR
 424 *         0 = inactive
 425 *         1 = active
 426 * B6    Ring Indicator (RI)
 427 *         0 = inactive
 428 *         1 = active
 429 * B7    Receive Line Signal Detect (RLSD)
 430 *         0 = inactive
 431 *         1 = active
 432 */
 433
 434
 435
 436/* Descriptors returned by the device
 437 *
 438 *  Device Descriptor
 439 *
 440 * Offset       Field           Size    Value   Description
 441 * 0    bLength         1       0x12    Size of descriptor in bytes
 442 * 1    bDescriptorType 1       0x01    DEVICE Descriptor Type
 443 * 2    bcdUSB          2       0x0110  USB Spec Release Number
 444 * 4    bDeviceClass    1       0x00    Class Code
 445 * 5    bDeviceSubClass 1       0x00    SubClass Code
 446 * 6    bDeviceProtocol 1       0x00    Protocol Code
 447 * 7    bMaxPacketSize0 1       0x08    Maximum packet size for endpoint 0
 448 * 8    idVendor        2       0x0403  Vendor ID
 449 * 10   idProduct       2       0x8372  Product ID (FTDI_SIO_PID)
 450 * 12   bcdDevice       2       0x0001  Device release number
 451 * 14   iManufacturer   1       0x01    Index of man. string desc
 452 * 15   iProduct        1       0x02    Index of prod string desc
 453 * 16   iSerialNumber   1       0x02    Index of serial nmr string desc
 454 * 17   bNumConfigurations 1    0x01    Number of possible configurations
 455 *
 456 * Configuration Descriptor
 457 *
 458 * Offset       Field                   Size    Value
 459 * 0    bLength                 1       0x09    Size of descriptor in bytes
 460 * 1    bDescriptorType         1       0x02    CONFIGURATION Descriptor Type
 461 * 2    wTotalLength            2       0x0020  Total length of data
 462 * 4    bNumInterfaces          1       0x01    Number of interfaces supported
 463 * 5    bConfigurationValue     1       0x01    Argument for SetCOnfiguration() req
 464 * 6    iConfiguration          1       0x02    Index of config string descriptor
 465 * 7    bmAttributes            1       0x20    Config characteristics Remote Wakeup
 466 * 8    MaxPower                1       0x1E    Max power consumption
 467 *
 468 * Interface Descriptor
 469 *
 470 * Offset       Field                   Size    Value
 471 * 0    bLength                 1       0x09    Size of descriptor in bytes
 472 * 1    bDescriptorType         1       0x04    INTERFACE Descriptor Type
 473 * 2    bInterfaceNumber        1       0x00    Number of interface
 474 * 3    bAlternateSetting       1       0x00    Value used to select alternate
 475 * 4    bNumEndpoints           1       0x02    Number of endpoints
 476 * 5    bInterfaceClass         1       0xFF    Class Code
 477 * 6    bInterfaceSubClass      1       0xFF    Subclass Code
 478 * 7    bInterfaceProtocol      1       0xFF    Protocol Code
 479 * 8    iInterface              1       0x02    Index of interface string description
 480 *
 481 * IN Endpoint Descriptor
 482 *
 483 * Offset       Field                   Size    Value
 484 * 0    bLength                 1       0x07    Size of descriptor in bytes
 485 * 1    bDescriptorType         1       0x05    ENDPOINT descriptor type
 486 * 2    bEndpointAddress        1       0x82    Address of endpoint
 487 * 3    bmAttributes            1       0x02    Endpoint attributes - Bulk
 488 * 4    bNumEndpoints           2       0x0040  maximum packet size
 489 * 5    bInterval               1       0x00    Interval for polling endpoint
 490 *
 491 * OUT Endpoint Descriptor
 492 *
 493 * Offset       Field                   Size    Value
 494 * 0    bLength                 1       0x07    Size of descriptor in bytes
 495 * 1    bDescriptorType         1       0x05    ENDPOINT descriptor type
 496 * 2    bEndpointAddress        1       0x02    Address of endpoint
 497 * 3    bmAttributes            1       0x02    Endpoint attributes - Bulk
 498 * 4    bNumEndpoints           2       0x0040  maximum packet size
 499 * 5    bInterval               1       0x00    Interval for polling endpoint
 500 *
 501 * DATA FORMAT
 502 *
 503 * IN Endpoint
 504 *
 505 * The device reserves the first two bytes of data on this endpoint to contain
 506 * the current values of the modem and line status registers. In the absence of
 507 * data, the device generates a message consisting of these two status bytes
 508 * every 40 ms
 509 *
 510 * Byte 0: Modem Status
 511 *
 512 * Offset       Description
 513 * B0   Reserved - must be 1
 514 * B1   Reserved - must be 0
 515 * B2   Reserved - must be 0
 516 * B3   Reserved - must be 0
 517 * B4   Clear to Send (CTS)
 518 * B5   Data Set Ready (DSR)
 519 * B6   Ring Indicator (RI)
 520 * B7   Receive Line Signal Detect (RLSD)
 521 *
 522 * Byte 1: Line Status
 523 *
 524 * Offset       Description
 525 * B0   Data Ready (DR)
 526 * B1   Overrun Error (OE)
 527 * B2   Parity Error (PE)
 528 * B3   Framing Error (FE)
 529 * B4   Break Interrupt (BI)
 530 * B5   Transmitter Holding Register (THRE)
 531 * B6   Transmitter Empty (TEMT)
 532 * B7   Error in RCVR FIFO
 533 *
 534 */
 535#define FTDI_RS0_CTS    (1 << 4)
 536#define FTDI_RS0_DSR    (1 << 5)
 537#define FTDI_RS0_RI     (1 << 6)
 538#define FTDI_RS0_RLSD   (1 << 7)
 539
 540#define FTDI_RS_DR      1
 541#define FTDI_RS_OE      (1<<1)
 542#define FTDI_RS_PE      (1<<2)
 543#define FTDI_RS_FE      (1<<3)
 544#define FTDI_RS_BI      (1<<4)
 545#define FTDI_RS_THRE    (1<<5)
 546#define FTDI_RS_TEMT    (1<<6)
 547#define FTDI_RS_FIFO    (1<<7)
 548
 549/*
 550 * OUT Endpoint
 551 *
 552 * This device reserves the first bytes of data on this endpoint contain the
 553 * length and port identifier of the message. For the FTDI USB Serial converter
 554 * the port identifier is always 1.
 555 *
 556 * Byte 0: Line Status
 557 *
 558 * Offset       Description
 559 * B0   Reserved - must be 1
 560 * B1   Reserved - must be 0
 561 * B2..7        Length of message - (not including Byte 0)
 562 *
 563 */
 564
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