diff options
| -rw-r--r-- | drivers/usb/serial/pl2303.c | 62 |
1 files changed, 52 insertions, 10 deletions
diff --git a/drivers/usb/serial/pl2303.c b/drivers/usb/serial/pl2303.c index 2448201..b93b3b3 100644 --- a/drivers/usb/serial/pl2303.c +++ b/drivers/usb/serial/pl2303.c @@ -4,6 +4,11 @@ * Copyright (C) 2001-2007 Greg Kroah-Hartman (greg@kroah.com) * Copyright (C) 2003 IBM Corp. * + * Copyright (C) 2009, 2013 Frank Schäfer <fschaefer.oss@googlemail.com> + * - fixes, improvements and documentation for the baud rate encoding methods + * Copyright (C) 2013 Reinhard Max <max@suse.de> + * - fixes and improvements for the divisor based baud rate encoding method + * * Original driver for 2.2.x by anonymous * * This program is free software; you can redistribute it and/or @@ -310,21 +315,58 @@ static void pl2303_encode_baudrate(struct tty_struct *tty, put_unaligned_le32(baud, buf); } else { /* + * Divisor based baud rate encoding method + * * NOTE: it's not clear if the type_0/1 chips * support this method * - * Apparently the formula for higher speeds is: - * baudrate = 12M * 32 / (2^buf[1]) / buf[0] + * divisor = 12MHz * 32 / baudrate = 2^A * B + * + * with + * + * A = buf[1] & 0x0e + * B = buf[0] + (buf[1] & 0x01) << 8 + * + * Special cases: + * => 8 < B < 16: device seems to work not properly + * => B <= 8: device uses the max. value B = 512 instead */ - unsigned tmp = 12000000 * 32 / baud; - buf[3] = 0x80; - buf[2] = 0; - buf[1] = (tmp >= 256); - while (tmp >= 256) { - tmp >>= 2; - buf[1] <<= 1; + + /* Determine factors A and B */ + unsigned int A = 0; + unsigned int B = 12000000 * 32 / baud; /* 12MHz */ + B <<= 1; /* Add one bit for rounding */ + while (B > (512 << 1) && A <= 14) { + A += 2; + B >>= 2; } - buf[0] = tmp; + if (A > 14) { /* max. divisor = min. baudrate reached */ + A = 14; + B = 512; + /* => ~45.78 baud */ + } else { + B = (B + 1) >> 1; /* Round the last bit */ + } + /* Handle special cases */ + if (B == 512) + B = 0; /* also: 1 to 8 */ + else if (B < 16) + /* + * NOTE: With the current algorithm this happens + * only for A=0 and means that the min. divisor + * (respectively: the max. baudrate) is reached. + */ + B = 16; /* => 24 MBaud */ + /* Encode the baud rate */ + buf[3] = 0x80; /* Select divisor encoding method */ + buf[2] = 0; + buf[1] = (A & 0x0e); /* A */ + buf[1] |= ((B & 0x100) >> 8); /* MSB of B */ + buf[0] = B & 0xff; /* 8 LSBs of B */ + /* Calculate the actual/resulting baud rate */ + if (B <= 8) + B = 512; + baud = 12000000 * 32 / ((1 << A) * B); } /* Save resulting baud rate */ |