Allow custom baud rates for FTDI serial ports

- Termios: cf{get,set}{i,o}speed can handle arbitrary speed values.
- The value is stored in the appropriate fields of the termios structure
  in this case. The old constants (stored in the flags) are preserved
  for BeOS binary compatibility.
- Adjust the FTDI FT232* driver to accept custom rates, by replacing the
  hardcoded regster values with a function that will compute it
  according to FTDI documentation (confirmed giving the same values for
  the existing baudrates).

headers/posix/termios.h

@@ -21,8 +21,8 @@ struct termios {
 	tcflag_t	c_cflag;	/* control modes */
 	tcflag_t	c_lflag;	/* local modes */
 	char		c_line;		/* line discipline */
-	speed_t		c_ispeed;	/* (unused) */
-	speed_t		c_ospeed;	/* (unused) */
+	speed_t		c_ispeed;	/* custom input baudrate */
+	speed_t		c_ospeed;	/* custom output baudrate */
 	cc_t		c_cc[NCCS];	/* control characters */
 };
 

src/add-ons/kernel/drivers/ports/usb_serial/FTDI.cpp

@@ -111,26 +111,24 @@ FTDIDevice::SetLineCoding(usb_cdc_line_coding *lineCoding)
 			break;
 		}
 	} else {
-		switch (lineCoding->speed) {
-			case 300: rate = ftdi_8u232am_b300; break;
-			case 600: rate = ftdi_8u232am_b600; break;
-			case 1200: rate = ftdi_8u232am_b1200; break;
-			case 2400: rate = ftdi_8u232am_b2400; break;
-			case 4800: rate = ftdi_8u232am_b4800; break;
-			case 9600: rate = ftdi_8u232am_b9600; break;
-			case 19200: rate = ftdi_8u232am_b19200; break;
-			case 38400: rate = ftdi_8u232am_b38400; break;
-			case 57600: rate = ftdi_8u232am_b57600; break;
-			case 115200: rate = ftdi_8u232am_b115200; break;
-			case 230400: rate = ftdi_8u232am_b230400; break;
-			case 460800: rate = ftdi_8u232am_b460800; break;
-			case 921600: rate = ftdi_8u232am_b921600; break;
-			default:
-				rate = ftdi_sio_b19200;
+		/* Compute baudrate register value as documented in AN232B-05 from FTDI.
+		 Bits 13-0 are the integer divider, and bits 16-14 are the fractional
+		 divider setting. 3Mbaud and 2Mbaud are special values, and at such
+		 high speeds the use of the fractional divider is not possible. */
+		if (lineCoding->speed == 3000000)
+			rate = 0;
+		else if (lineCoding->speed == 2000000)
+			rate = 1;
+		else {
+			if (lineCoding->speed > 1500000) {
 				TRACE_ALWAYS("= FTDIDevice::SetLineCoding(): Datarate: %d is "
 					"not supported by this hardware. Defaulted to %d\n",
-					lineCoding->speed, rate);
-				break;
+					lineCoding->speed, 19200);
+				lineCoding->speed = 19200;
+			}
+			rate = 3000000 * 8 / lineCoding->speed;
+			int frac = ftdi_8u232am_frac[rate & 0x7];
+			rate = (rate >> 3) | frac;
 		}
 	}
 

src/add-ons/kernel/drivers/ports/usb_serial/FTDIRegs.h

@@ -101,20 +101,17 @@ enum {
 	ftdi_sio_b115200 = 9
 };
 
-enum {
-	ftdi_8u232am_b300 = 0x2710,
-	ftdi_8u232am_b600 = 0x1388,
-	ftdi_8u232am_b1200 = 0x09c4,
-	ftdi_8u232am_b2400 = 0x04e2,
-	ftdi_8u232am_b4800 = 0x0271,
-	ftdi_8u232am_b9600 = 0x4138,
-	ftdi_8u232am_b19200 = 0x809c,
-	ftdi_8u232am_b38400 = 0xc04e,
-	ftdi_8u232am_b57600 = 0x0034,
-	ftdi_8u232am_b115200 = 0x001a,
-	ftdi_8u232am_b230400 = 0x000d,
-	ftdi_8u232am_b460800 = 0x4006,
-	ftdi_8u232am_b921600 = 0x8003
+
+/* Fractional divider values for FT232A/B devices */
+static const int ftdi_8u232am_frac[8] = {
+	0x0 << 14, /* .0   */
+	0x3 << 14, /* .125 */
+	0x2 << 14, /* .25  */
+	0x4 << 14, /* .375 */
+	0x1 << 14, /* .5   */
+	0x5 << 14, /* .625 */
+	0x6 << 14, /* .75  */
+	0x7 << 14 /* .875 */
 };
 
 /*

src/add-ons/kernel/drivers/ports/usb_serial/SerialDevice.cpp

@@ -161,8 +161,8 @@ SerialDevice::SetModes(struct termios *tios)
 	uint8 baud = tios->c_cflag & CBAUD;
 	int32 speed = baud_index_to_speed(baud);
 	if (speed < 0) {
-		baud = B19200;
-		speed = 19200;
+		baud = CBAUD;
+		speed = tios->c_ospeed;
 	}
 
 	// update our master config in full

src/system/libroot/posix/termios.c

@@ -105,6 +105,11 @@ tcsendbreak(int fd, int duration)
 speed_t
 cfgetispeed(const struct termios *termios)
 {
+	if (termios->c_cflag & CBAUD == CBAUD)
+	{
+		return termios->c_ispeed;
+	}
+
 	return termios->c_cflag & CBAUD;
 }
 
@@ -112,14 +117,14 @@ cfgetispeed(const struct termios *termios)
 int
 cfsetispeed(struct termios *termios, speed_t speed)
 {
-	/*	Check for values that the system cannot handle:
-	greater values than B230400 which is
-	the maximum value defined in termios.h
-	Note that errors from hardware device are detected only
-	until the tcsetattr() function is called */
-	if (speed > B230400 || (speed & CBAUD) != speed) {
-		__set_errno(EINVAL);
-		return -1;
+	/*	Check for custom baudrates, which must be stored in the c_ispeed
+	field instead of inlined in the flags.
+	Note that errors from hardware device (unsupported baudrates, etc) are
+	detected only when the tcsetattr() function is called */
+	if (speed > B31250) {
+		termios->c_cflag |= CBAUD;
+		termios->c_ispeed = speed;
+		return 0;
 	}
 
 	termios->c_cflag &= ~CBAUD;
@@ -131,6 +136,11 @@ cfsetispeed(struct termios *termios, speed_t speed)
 speed_t
 cfgetospeed(const struct termios *termios)
 {
+	if (termios->c_cflag & CBAUD == CBAUD)
+	{
+		return termios->c_ospeed;
+	}
+
 	return termios->c_cflag & CBAUD;
 }
 
@@ -138,10 +148,11 @@ cfgetospeed(const struct termios *termios)
 int
 cfsetospeed(struct termios *termios, speed_t speed)
 {
-	/* Check for unaccepted speed values (see above) */
-	if (speed > B230400 || (speed & CBAUD) != speed) {
-		__set_errno(EINVAL);
-		return -1;
+	/* Check for custom speed values (see above) */
+	if (speed > B31250) {
+		termios->c_cflag |= CBAUD;
+		termios->c_ospeed = speed;
+		return 0;
 	}
 
 	termios->c_cflag &= ~CBAUD;