From: "Michael G. Katzmann" <michaelk@IEEE.org>
To: Johan Hovold <johan@kernel.org>, Charles Yeh <charlesyeh522@gmail.com>
Cc: "Yeh.Charles [葉榮鑫]" <charles-yeh@prolific.com.tw>,
linux-serial@vger.kernel.org, linux-usb@vger.kernel.org,
"Joe Abbott" <jabbott@rollanet.org>
Subject: Re: non-standard baud rates with Prolific 2303 USB-serial
Date: Sat, 6 Mar 2021 15:18:45 -0500 [thread overview]
Message-ID: <3c8b6bca-4f8f-f537-7f88-9815715a7b14@IEEE.org> (raw)
In-Reply-To: <YEH7okblCx8+Odxn@hovoldconsulting.com>
On 3/5/21 4:36 AM, Johan Hovold wrote:
> On Fri, Mar 05, 2021 at 05:32:23PM +0800, Charles Yeh wrote:
>> 110 bps is not the standard Baud rate,
>> PL2303TA don't work with the current Linux driver (d5 0e 00 80), It
>> needs to "a8 a6 01 80"
>
> Ok, thanks for confirming. Then we should be able to fix this up based
> on Michael's findings.
>
>> Johan Hovold <johan@kernel.org> 於 2021年2月25日 週四 上午1:00寫道:
>>
>>> But can you confirm that your PL2303TA works with the current Linux
>>> driver at 110 Bd (and doesn't need the alternate divisor encoding)?
>
> Johan
>
How about... altering the call to pl2303_encode_baud_rate_divisor (adding 'port')
baud = pl2303_encode_baud_rate_divisor(port, buf, baud);
and checking for model and altering algorithm as below.
I've tested this on the TA version.
Michael
static speed_t pl2303_encode_baud_rate_divisor(struct usb_serial_port *port, unsigned char buf[4],
speed_t baud)
{
unsigned int baseline, mantissa, exponent;
unsigned int bcdDevice = port->serial->dev->descriptor.bcdDevice;
unsigned int bcdUSB = port->serial->dev->descriptor.bcdUSB;
enum model { eUNKNOWN, eHXD, eHXA, eTA } model;
if ( bcdUSB == 0x0110 ) {
if( bcdDevice == 0x0400 )
model = eHXD;
else if ( bcdDevice == 0x0300 )
model = eHXA; // PL2303HX(A)/XA ( EOL : PHASED OUT SINCE 2012 )
else
model = eUNKNOWN;
} else if( bcdUSB == 0x200 && bcdDevice == 0x0300 ) {
model = eTA;
}
/*
* Apparently the formula is:
* baudrate = 12M * 32 / (mantissa * 4^exponent)
* where
* mantissa = buf[8:0]
* exponent = buf[11:9]
*
* TA version has more precision
* uses mantissa = buf[bits 10:0 ]
* exponent = buf[bits 15:13]
* and x2 prescaler enable by buf[bit 16]
*/
baseline = 12000000 * 32;
mantissa = baseline / baud;
if (mantissa == 0)
mantissa = 1; /* Avoid dividing by zero if baud > 32*12M. */
exponent = 0;
if ( model == eTA ) {
while (mantissa >= 2048) {
// n.b. below is speculative for the TA chip and is based on original code
if (exponent < 15) { // we are going to divide this by 2 later
mantissa >>= 1; // divide by 2
exponent++; // currently log2 ... will become log4
} else {
/* Exponent is maxed. Trim mantissa and leave. */
mantissa = 2047 ;
break;
}
}
buf[2] = exponent & 0x01; // activate x2 prescaler if needed
exponent >>= 1; // now log base 4 (losing LSB)
buf[1] = (exponent << 5) | (mantissa >> 8);
} else {
while (mantissa >= 512) {
if (exponent < 7) {
mantissa >>= 2; /* divide by 4 */
exponent++;
} else {
/* Exponent is maxed. Trim mantissa and leave. */
mantissa = 511;
break;
}
}
buf[2] = 0;
buf[1] = exponent << 1 | mantissa >> 8;
}
buf[3] = 0x80;
buf[0] = mantissa & 0xff;
/* Calculate and return the exact baud rate. */
baud = (baseline / mantissa / (buf[2] == 0x01 ? 2:1)) >> (exponent << 1);
return baud;
}
next prev parent reply other threads:[~2021-03-06 20:19 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <3aee5708-7961-f464-8c5f-6685d96920d6@IEEE.org>
[not found] ` <dc3458f1-830b-284b-3464-20124dc3900a@IEEE.org>
2021-02-22 8:52 ` non-standard baud rates with Prolific 2303 USB-serial Johan Hovold
2021-02-22 12:39 ` Michael G. Katzmann
2021-02-22 13:18 ` Johan Hovold
[not found] ` <fb1489c2-b972-619b-b7ce-4ae8e1d2cc0f@IEEE.org>
2021-02-22 15:34 ` Johan Hovold
2021-02-22 15:42 ` Michael G. Katzmann
2021-02-22 15:50 ` Johan Hovold
2021-02-22 16:37 ` Michael G. Katzmann
2021-02-22 16:48 ` Johan Hovold
2021-02-24 23:08 ` Joe Abbott
2021-02-25 8:44 ` Johan Hovold
[not found] ` <43da22ced8e14442bbc8babea77e4ed7@MailHC2.prolific.com.tw>
2021-02-23 10:18 ` Johan Hovold
2021-02-23 13:25 ` Michael G. Katzmann
2021-02-23 14:58 ` Michael G. Katzmann
2021-02-23 15:43 ` Johan Hovold
2021-02-23 15:57 ` Michael G. Katzmann
2021-02-23 16:14 ` Johan Hovold
2021-02-23 16:30 ` Michael G. Katzmann
2021-02-23 16:52 ` Johan Hovold
2021-02-23 19:15 ` Michael G. Katzmann
2021-02-24 17:04 ` Johan Hovold
2021-02-24 18:13 ` Michael G. Katzmann
2021-02-25 8:42 ` Johan Hovold
2021-04-08 15:35 ` Johan Hovold
2021-02-24 7:34 ` Charles Yeh
2021-02-24 17:00 ` Johan Hovold
2021-02-24 17:12 ` Michael G. Katzmann
2021-03-05 9:32 ` Charles Yeh
2021-03-05 9:36 ` Johan Hovold
2021-03-06 20:18 ` Michael G. Katzmann [this message]
2021-03-07 4:15 ` Michael G. Katzmann
2021-03-11 16:08 ` Johan Hovold
2021-03-12 13:17 ` Michael G. Katzmann
2021-03-12 13:44 ` Johan Hovold
2021-03-12 20:29 ` Michael G. Katzmann
2021-03-13 1:28 ` Michael G. Katzmann
2021-03-15 9:07 ` Johan Hovold
2021-03-15 10:07 ` Charles Yeh
2021-03-15 10:24 ` Johan Hovold
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