/* $OpenBSD: uftdi.c,v 1.30 2006/06/23 06:27:11 miod Exp $ */ /* $NetBSD: uftdi.c,v 1.14 2003/02/23 04:20:07 simonb Exp $ */ /* * Copyright (c) 2000 The NetBSD Foundation, Inc. * All rights reserved. * * This code is derived from software contributed to The NetBSD Foundation * by Lennart Augustsson (lennart@augustsson.net). * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * 3. All advertising materials mentioning features or use of this software * must display the following acknowledgement: * This product includes software developed by the NetBSD * Foundation, Inc. and its contributors. * 4. Neither the name of The NetBSD Foundation nor the names of its * contributors may be used to endorse or promote products derived * from this software without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE * POSSIBILITY OF SUCH DAMAGE. */ /* * FTDI FT8U100AX serial adapter driver */ /* * XXX This driver will not support multiple serial ports. * XXX The ucom layer needs to be extended first. */ #include #include #include #include #include #include #include #include #include #include #include #include #include #ifdef UFTDI_DEBUG #define DPRINTF(x) do { if (uftdidebug) printf x; } while (0) #define DPRINTFN(n,x) do { if (uftdidebug>(n)) printf x; } while (0) int uftdidebug = 0; #else #define DPRINTF(x) #define DPRINTFN(n,x) #endif #define UFTDI_CONFIG_INDEX 0 #define UFTDI_IFACE_INDEX 0 /* * These are the maximum number of bytes transferred per frame. * The output buffer size cannot be increased due to the size encoding. */ #define UFTDIIBUFSIZE 64 #define UFTDIOBUFSIZE 64 struct uftdi_softc { USBBASEDEVICE sc_dev; /* base device */ usbd_device_handle sc_udev; /* device */ usbd_interface_handle sc_iface; /* interface */ enum uftdi_type sc_type; u_int sc_hdrlen; u_char sc_msr; u_char sc_lsr; device_ptr_t sc_subdev; u_char sc_dying; u_int last_lcr; }; Static void uftdi_get_status(void *, int portno, u_char *lsr, u_char *msr); Static void uftdi_set(void *, int, int, int); Static int uftdi_param(void *, int, struct termios *); Static int uftdi_open(void *sc, int portno); Static void uftdi_read(void *sc, int portno, u_char **ptr, u_int32_t *count); Static void uftdi_write(void *sc, int portno, u_char *to, u_char *from, u_int32_t *count); Static void uftdi_break(void *sc, int portno, int onoff); Static int uftdi_8u232am_getrate(speed_t speed, int *rate); struct ucom_methods uftdi_methods = { uftdi_get_status, uftdi_set, uftdi_param, NULL, uftdi_open, NULL, uftdi_read, uftdi_write, }; USB_DECLARE_DRIVER(uftdi); USB_MATCH(uftdi) { USB_MATCH_START(uftdi, uaa); if (uaa->iface != NULL) { if (uaa->vendor == USB_VENDOR_FTDI && (uaa->product == USB_PRODUCT_FTDI_SERIAL_2232C)) return (UMATCH_VENDOR_IFACESUBCLASS); return (UMATCH_NONE); } DPRINTFN(20,("uftdi: vendor=0x%x, product=0x%x\n", uaa->vendor, uaa->product)); if (uaa->vendor == USB_VENDOR_FTDI && (uaa->product == USB_PRODUCT_FTDI_SERIAL_8U100AX || uaa->product == USB_PRODUCT_FTDI_SERIAL_8U232AM || uaa->product == USB_PRODUCT_FTDI_SEMC_DSS20 || uaa->product == USB_PRODUCT_FTDI_MHAM_KW || uaa->product == USB_PRODUCT_FTDI_MHAM_YS || uaa->product == USB_PRODUCT_FTDI_MHAM_Y6 || uaa->product == USB_PRODUCT_FTDI_MHAM_Y8 || uaa->product == USB_PRODUCT_FTDI_MHAM_IC || uaa->product == USB_PRODUCT_FTDI_MHAM_DB9 || uaa->product == USB_PRODUCT_FTDI_MHAM_RS232 || uaa->product == USB_PRODUCT_FTDI_MHAM_Y9 || uaa->product == USB_PRODUCT_FTDI_LCD_LK202_24 || uaa->product == USB_PRODUCT_FTDI_LCD_LK204_24 || uaa->product == USB_PRODUCT_FTDI_LCD_MX200 || uaa->product == USB_PRODUCT_FTDI_LCD_CFA_631 || uaa->product == USB_PRODUCT_FTDI_LCD_CFA_632 || uaa->product == USB_PRODUCT_FTDI_LCD_CFA_633 || uaa->product == USB_PRODUCT_FTDI_LCD_CFA_634)) return (UMATCH_VENDOR_PRODUCT); if (uaa->vendor == USB_VENDOR_SIIG2 && (uaa->product == USB_PRODUCT_SIIG2_US2308)) return (UMATCH_VENDOR_PRODUCT); if (uaa->vendor == USB_VENDOR_INTREPIDCS && (uaa->product == USB_PRODUCT_INTREPIDCS_VALUECAN || uaa->product == USB_PRODUCT_INTREPIDCS_NEOVI)) return (UMATCH_VENDOR_PRODUCT); if (uaa->vendor == USB_VENDOR_BBELECTRONICS && (uaa->product == USB_PRODUCT_BBELECTRONICS_USOTL4)) return (UMATCH_VENDOR_PRODUCT); if (uaa->vendor == USB_VENDOR_FALCOM && (uaa->product == USB_PRODUCT_FALCOM_TWIST || uaa->product == USB_PRODUCT_FALCOM_SAMBA)) return (UMATCH_VENDOR_PRODUCT); if (uaa->vendor == USB_VENDOR_SEALEVEL && uaa->product == USB_PRODUCT_SEALEVEL_USBSERIAL) return (UMATCH_VENDOR_PRODUCT); return (UMATCH_NONE); } USB_ATTACH(uftdi) { USB_ATTACH_START(uftdi, sc, uaa); usbd_device_handle dev = uaa->device; usbd_interface_handle iface; usb_interface_descriptor_t *id; usb_endpoint_descriptor_t *ed; char *devinfop; char *devname = USBDEVNAME(sc->sc_dev); int i; usbd_status err; struct ucom_attach_args uca; DPRINTFN(10,("\nuftdi_attach: sc=%p\n", sc)); if (uaa->iface == NULL) { /* Move the device into the configured state. */ err = usbd_set_config_index(dev, UFTDI_CONFIG_INDEX, 1); if (err) { printf("\n%s: failed to set configuration, err=%s\n", devname, usbd_errstr(err)); goto bad; } err = usbd_device2interface_handle(dev, UFTDI_IFACE_INDEX, &iface); if (err) { printf("\n%s: failed to get interface, err=%s\n", devname, usbd_errstr(err)); goto bad; } } else iface = uaa->iface; devinfop = usbd_devinfo_alloc(dev, 0); USB_ATTACH_SETUP; printf("%s: %s\n", devname, devinfop); usbd_devinfo_free(devinfop); id = usbd_get_interface_descriptor(iface); sc->sc_udev = dev; sc->sc_iface = iface; switch (uaa->vendor) { case USB_VENDOR_FTDI: switch (uaa->product) { case USB_PRODUCT_FTDI_SERIAL_8U100AX: sc->sc_type = UFTDI_TYPE_SIO; sc->sc_hdrlen = 1; break; case USB_PRODUCT_FTDI_SEMC_DSS20: case USB_PRODUCT_FTDI_SERIAL_8U232AM: case USB_PRODUCT_FTDI_SERIAL_2232C: case USB_PRODUCT_FTDI_LCD_LK202_24: case USB_PRODUCT_FTDI_LCD_LK204_24: case USB_PRODUCT_FTDI_LCD_MX200: case USB_PRODUCT_FTDI_LCD_CFA_631: case USB_PRODUCT_FTDI_LCD_CFA_632: case USB_PRODUCT_FTDI_LCD_CFA_633: case USB_PRODUCT_FTDI_LCD_CFA_634: case USB_PRODUCT_FTDI_MHAM_KW: case USB_PRODUCT_FTDI_MHAM_YS: case USB_PRODUCT_FTDI_MHAM_Y6: case USB_PRODUCT_FTDI_MHAM_Y8: case USB_PRODUCT_FTDI_MHAM_IC: case USB_PRODUCT_FTDI_MHAM_DB9: case USB_PRODUCT_FTDI_MHAM_RS232: case USB_PRODUCT_FTDI_MHAM_Y9: case USB_PRODUCT_SEALEVEL_USBSERIAL: sc->sc_type = UFTDI_TYPE_8U232AM; sc->sc_hdrlen = 0; break; default: /* Can't happen */ goto bad; } break; case USB_VENDOR_INTREPIDCS: switch (uaa->product) { case USB_PRODUCT_INTREPIDCS_VALUECAN: case USB_PRODUCT_INTREPIDCS_NEOVI: sc->sc_type = UFTDI_TYPE_8U232AM; sc->sc_hdrlen = 0; break; default: /* Can't happen */ goto bad; } break; case USB_VENDOR_SIIG2: switch (uaa->product) { case USB_PRODUCT_SIIG2_US2308: sc->sc_type = UFTDI_TYPE_8U232AM; sc->sc_hdrlen = 0; break; default: /* Can't happen */ goto bad; } break; case USB_VENDOR_BBELECTRONICS: switch( uaa->product ){ case USB_PRODUCT_BBELECTRONICS_USOTL4: sc->sc_type = UFTDI_TYPE_8U232AM; sc->sc_hdrlen = 0; break; default: /* Can't happen */ goto bad; } break; case USB_VENDOR_FALCOM: switch( uaa->product ){ case USB_PRODUCT_FALCOM_TWIST: case USB_PRODUCT_FALCOM_SAMBA: sc->sc_type = UFTDI_TYPE_8U232AM; sc->sc_hdrlen = 0; break; default: /* Can't happen */ goto bad; } break; } uca.bulkin = uca.bulkout = -1; for (i = 0; i < id->bNumEndpoints; i++) { int addr, dir, attr; ed = usbd_interface2endpoint_descriptor(iface, i); if (ed == NULL) { printf("%s: could not read endpoint descriptor\n", devname); goto bad; } addr = ed->bEndpointAddress; dir = UE_GET_DIR(ed->bEndpointAddress); attr = ed->bmAttributes & UE_XFERTYPE; if (dir == UE_DIR_IN && attr == UE_BULK) uca.bulkin = addr; else if (dir == UE_DIR_OUT && attr == UE_BULK) uca.bulkout = addr; else { printf("%s: unexpected endpoint\n", devname); goto bad; } } if (uca.bulkin == -1) { printf("%s: Could not find data bulk in\n", USBDEVNAME(sc->sc_dev)); goto bad; } if (uca.bulkout == -1) { printf("%s: Could not find data bulk out\n", USBDEVNAME(sc->sc_dev)); goto bad; } if (uaa->iface == NULL) uca.portno = FTDI_PIT_SIOA; else uca.portno = FTDI_PIT_SIOA + id->bInterfaceNumber; /* bulkin, bulkout set above */ uca.ibufsize = UFTDIIBUFSIZE; uca.obufsize = UFTDIOBUFSIZE - sc->sc_hdrlen; uca.ibufsizepad = UFTDIIBUFSIZE; uca.opkthdrlen = sc->sc_hdrlen; uca.device = dev; uca.iface = iface; uca.methods = &uftdi_methods; uca.arg = sc; uca.info = NULL; usbd_add_drv_event(USB_EVENT_DRIVER_ATTACH, sc->sc_udev, USBDEV(sc->sc_dev)); DPRINTF(("uftdi: in=0x%x out=0x%x\n", uca.bulkin, uca.bulkout)); sc->sc_subdev = config_found_sm(self, &uca, ucomprint, ucomsubmatch); USB_ATTACH_SUCCESS_RETURN; bad: DPRINTF(("uftdi_attach: ATTACH ERROR\n")); sc->sc_dying = 1; USB_ATTACH_ERROR_RETURN; } int uftdi_activate(device_ptr_t self, enum devact act) { struct uftdi_softc *sc = (struct uftdi_softc *)self; int rv = 0; switch (act) { case DVACT_ACTIVATE: break; case DVACT_DEACTIVATE: if (sc->sc_subdev != NULL) rv = config_deactivate(sc->sc_subdev); sc->sc_dying = 1; break; } return (rv); } int uftdi_detach(device_ptr_t self, int flags) { struct uftdi_softc *sc = (struct uftdi_softc *)self; DPRINTF(("uftdi_detach: sc=%p flags=%d\n", sc, flags)); sc->sc_dying = 1; if (sc->sc_subdev != NULL) { config_detach(sc->sc_subdev, flags); sc->sc_subdev = NULL; } usbd_add_drv_event(USB_EVENT_DRIVER_DETACH, sc->sc_udev, USBDEV(sc->sc_dev)); return (0); } Static int uftdi_open(void *vsc, int portno) { struct uftdi_softc *sc = vsc; usb_device_request_t req; usbd_status err; struct termios t; DPRINTF(("uftdi_open: sc=%p\n", sc)); if (sc->sc_dying) return (EIO); /* Perform a full reset on the device */ req.bmRequestType = UT_WRITE_VENDOR_DEVICE; req.bRequest = FTDI_SIO_RESET; USETW(req.wValue, FTDI_SIO_RESET_SIO); USETW(req.wIndex, portno); USETW(req.wLength, 0); err = usbd_do_request(sc->sc_udev, &req, NULL); if (err) return (EIO); /* Set 9600 baud, 2 stop bits, no parity, 8 bits */ t.c_ospeed = 9600; t.c_cflag = CSTOPB | CS8; (void)uftdi_param(sc, portno, &t); /* Turn on RTS/CTS flow control */ req.bmRequestType = UT_WRITE_VENDOR_DEVICE; req.bRequest = FTDI_SIO_SET_FLOW_CTRL; USETW(req.wValue, 0); USETW2(req.wIndex, FTDI_SIO_RTS_CTS_HS, portno); USETW(req.wLength, 0); err = usbd_do_request(sc->sc_udev, &req, NULL); if (err) return (EIO); return (0); } Static void uftdi_read(void *vsc, int portno, u_char **ptr, u_int32_t *count) { struct uftdi_softc *sc = vsc; u_char msr, lsr; DPRINTFN(15,("uftdi_read: sc=%p, port=%d count=%d\n", sc, portno, *count)); msr = FTDI_GET_MSR(*ptr); lsr = FTDI_GET_LSR(*ptr); #ifdef UFTDI_DEBUG if (*count != 2) DPRINTFN(10,("uftdi_read: sc=%p, port=%d count=%d data[0]=" "0x%02x\n", sc, portno, *count, (*ptr)[2])); #endif if (sc->sc_msr != msr || (sc->sc_lsr & FTDI_LSR_MASK) != (lsr & FTDI_LSR_MASK)) { DPRINTF(("uftdi_read: status change msr=0x%02x(0x%02x) " "lsr=0x%02x(0x%02x)\n", msr, sc->sc_msr, lsr, sc->sc_lsr)); sc->sc_msr = msr; sc->sc_lsr = lsr; ucom_status_change((struct ucom_softc *)sc->sc_subdev); } /* Pick up status and adjust data part. */ *ptr += 2; *count -= 2; } Static void uftdi_write(void *vsc, int portno, u_char *to, u_char *from, u_int32_t *count) { struct uftdi_softc *sc = vsc; DPRINTFN(10,("uftdi_write: sc=%p, port=%d count=%u data[0]=0x%02x\n", vsc, portno, *count, from[0])); /* Make length tag and copy data */ if (sc->sc_hdrlen > 0) *to = FTDI_OUT_TAG(*count, portno); memcpy(to + sc->sc_hdrlen, from, *count); *count += sc->sc_hdrlen; } Static void uftdi_set(void *vsc, int portno, int reg, int onoff) { struct uftdi_softc *sc = vsc; usb_device_request_t req; int ctl; DPRINTF(("uftdi_set: sc=%p, port=%d reg=%d onoff=%d\n", vsc, portno, reg, onoff)); switch (reg) { case UCOM_SET_DTR: ctl = onoff ? FTDI_SIO_SET_DTR_HIGH : FTDI_SIO_SET_DTR_LOW; break; case UCOM_SET_RTS: ctl = onoff ? FTDI_SIO_SET_RTS_HIGH : FTDI_SIO_SET_RTS_LOW; break; case UCOM_SET_BREAK: uftdi_break(sc, portno, onoff); return; default: return; } req.bmRequestType = UT_WRITE_VENDOR_DEVICE; req.bRequest = FTDI_SIO_MODEM_CTRL; USETW(req.wValue, ctl); USETW(req.wIndex, portno); USETW(req.wLength, 0); DPRINTFN(2,("uftdi_set: reqtype=0x%02x req=0x%02x value=0x%04x " "index=0x%04x len=%d\n", req.bmRequestType, req.bRequest, UGETW(req.wValue), UGETW(req.wIndex), UGETW(req.wLength))); (void)usbd_do_request(sc->sc_udev, &req, NULL); } Static int uftdi_param(void *vsc, int portno, struct termios *t) { struct uftdi_softc *sc = vsc; usb_device_request_t req; usbd_status err; int rate, data, flow; DPRINTF(("uftdi_param: sc=%p\n", sc)); if (sc->sc_dying) return (EIO); switch (sc->sc_type) { case UFTDI_TYPE_SIO: switch (t->c_ospeed) { case 300: rate = ftdi_sio_b300; break; case 600: rate = ftdi_sio_b600; break; case 1200: rate = ftdi_sio_b1200; break; case 2400: rate = ftdi_sio_b2400; break; case 4800: rate = ftdi_sio_b4800; break; case 9600: rate = ftdi_sio_b9600; break; case 19200: rate = ftdi_sio_b19200; break; case 38400: rate = ftdi_sio_b38400; break; case 57600: rate = ftdi_sio_b57600; break; case 115200: rate = ftdi_sio_b115200; break; default: return (EINVAL); } break; case UFTDI_TYPE_8U232AM: if (uftdi_8u232am_getrate(t->c_ospeed, &rate) == -1) return (EINVAL); break; } req.bmRequestType = UT_WRITE_VENDOR_DEVICE; req.bRequest = FTDI_SIO_SET_BAUD_RATE; USETW(req.wValue, rate); USETW(req.wIndex, portno); USETW(req.wLength, 0); DPRINTFN(2,("uftdi_param: reqtype=0x%02x req=0x%02x value=0x%04x " "index=0x%04x len=%d\n", req.bmRequestType, req.bRequest, UGETW(req.wValue), UGETW(req.wIndex), UGETW(req.wLength))); err = usbd_do_request(sc->sc_udev, &req, NULL); if (err) return (EIO); if (ISSET(t->c_cflag, CSTOPB)) data = FTDI_SIO_SET_DATA_STOP_BITS_2; else data = FTDI_SIO_SET_DATA_STOP_BITS_1; if (ISSET(t->c_cflag, PARENB)) { if (ISSET(t->c_cflag, PARODD)) data |= FTDI_SIO_SET_DATA_PARITY_ODD; else data |= FTDI_SIO_SET_DATA_PARITY_EVEN; } else data |= FTDI_SIO_SET_DATA_PARITY_NONE; switch (ISSET(t->c_cflag, CSIZE)) { case CS5: data |= FTDI_SIO_SET_DATA_BITS(5); break; case CS6: data |= FTDI_SIO_SET_DATA_BITS(6); break; case CS7: data |= FTDI_SIO_SET_DATA_BITS(7); break; case CS8: data |= FTDI_SIO_SET_DATA_BITS(8); break; } sc->last_lcr = data; req.bmRequestType = UT_WRITE_VENDOR_DEVICE; req.bRequest = FTDI_SIO_SET_DATA; USETW(req.wValue, data); USETW(req.wIndex, portno); USETW(req.wLength, 0); DPRINTFN(2,("uftdi_param: reqtype=0x%02x req=0x%02x value=0x%04x " "index=0x%04x len=%d\n", req.bmRequestType, req.bRequest, UGETW(req.wValue), UGETW(req.wIndex), UGETW(req.wLength))); err = usbd_do_request(sc->sc_udev, &req, NULL); if (err) return (EIO); if (ISSET(t->c_cflag, CRTSCTS)) { flow = FTDI_SIO_RTS_CTS_HS; USETW(req.wValue, 0); } else if (ISSET(t->c_iflag, IXON|IXOFF)) { flow = FTDI_SIO_XON_XOFF_HS; USETW2(req.wValue, t->c_cc[VSTOP], t->c_cc[VSTART]); } else { flow = FTDI_SIO_DISABLE_FLOW_CTRL; USETW(req.wValue, 0); } req.bmRequestType = UT_WRITE_VENDOR_DEVICE; req.bRequest = FTDI_SIO_SET_FLOW_CTRL; USETW2(req.wIndex, flow, portno); USETW(req.wLength, 0); err = usbd_do_request(sc->sc_udev, &req, NULL); if (err) return (EIO); return (0); } void uftdi_get_status(void *vsc, int portno, u_char *lsr, u_char *msr) { struct uftdi_softc *sc = vsc; DPRINTF(("uftdi_status: msr=0x%02x lsr=0x%02x\n", sc->sc_msr, sc->sc_lsr)); if (msr != NULL) *msr = sc->sc_msr; if (lsr != NULL) *lsr = sc->sc_lsr; } void uftdi_break(void *vsc, int portno, int onoff) { struct uftdi_softc *sc = vsc; usb_device_request_t req; int data; DPRINTF(("uftdi_break: sc=%p, port=%d onoff=%d\n", vsc, portno, onoff)); if (onoff) { data = sc->last_lcr | FTDI_SIO_SET_BREAK; } else { data = sc->last_lcr; } req.bmRequestType = UT_WRITE_VENDOR_DEVICE; req.bRequest = FTDI_SIO_SET_DATA; USETW(req.wValue, data); USETW(req.wIndex, portno); USETW(req.wLength, 0); (void)usbd_do_request(sc->sc_udev, &req, NULL); } Static int uftdi_8u232am_getrate(speed_t speed, int *rate) { /* Table of the nearest even powers-of-2 for values 0..15. */ static const unsigned char roundoff[16] = { 0, 2, 2, 4, 4, 4, 8, 8, 8, 8, 8, 8, 16, 16, 16, 16, }; unsigned int d, freq; int result; if (speed <= 0) return (-1); /* Special cases for 2M and 3M. */ if (speed >= 3000000 * 100 / 103 && speed <= 3000000 * 100 / 97) { result = 0; goto done; } if (speed >= 2000000 * 100 / 103 && speed <= 2000000 * 100 / 97) { result = 1; goto done; } d = (FTDI_8U232AM_FREQ << 4) / speed; d = (d & ~15) + roundoff[d & 15]; if (d < FTDI_8U232AM_MIN_DIV) d = FTDI_8U232AM_MIN_DIV; else if (d > FTDI_8U232AM_MAX_DIV) d = FTDI_8U232AM_MAX_DIV; /* * Calculate the frequency needed for d to exactly divide down * to our target speed, and check that the actual frequency is * within 3% of this. */ freq = speed * d; if (freq < (quad_t)(FTDI_8U232AM_FREQ << 4) * 100 / 103 || freq > (quad_t)(FTDI_8U232AM_FREQ << 4) * 100 / 97) return (-1); /* * Pack the divisor into the resultant value. The lower * 14-bits hold the integral part, while the upper 2 bits * encode the fractional component: either 0, 0.5, 0.25, or * 0.125. */ result = d >> 4; if (d & 8) result |= 0x4000; else if (d & 4) result |= 0x8000; else if (d & 2) result |= 0xc000; done: *rate = result; return (0); }