From: "Michael G. Katzmann" <michaelk@IEEE.org>
To: Johan Hovold <johan@kernel.org>
Cc: "Charles Yeh" <charlesyeh522@gmail.com>,
"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: Fri, 12 Mar 2021 20:28:04 -0500 [thread overview]
Message-ID: <a475110e-2f44-eeca-3cd2-dd946e5abfe7@IEEE.org> (raw)
In-Reply-To: <YEtwNzhCmvyKhRto@hovoldconsulting.com>
On 3/12/21 8:44 AM, Johan Hovold wrote:
Let me try that patch in the right format 8-)
--- a/drivers/usb/serial/pl2303.c 2021-03-12 09:30:22.963992109 -0500
+++ b/drivers/usb/serial/pl2303.c 2021-03-12 20:00:20.003526891 -0500
@@ -188,6 +188,7 @@
unsigned long quirks;
unsigned int no_autoxonxoff:1;
unsigned int no_divisors:1;
+ unsigned int alt_divisors:1;
};
struct pl2303_serial_private {
@@ -217,10 +218,12 @@
[TYPE_TA] = {
.name = "TA",
.max_baud_rate = 6000000,
+ .alt_divisors = true,
},
[TYPE_TB] = {
.name = "TB",
.max_baud_rate = 12000000,
+ .alt_divisors = true,
},
[TYPE_HXD] = {
.name = "HXD",
@@ -618,6 +621,46 @@
return baud;
}
+static speed_t pl2303_encode_baud_rate_divisor_alt(unsigned char buf[4],
+ speed_t baud)
+{
+ unsigned int baseline, mantissa, exponent;
+
+ /*
+ * Apparently, for the TA version the formula is:
+ * baudrate = 12M * 32 / (mantissa * 2^exponent)
+ * where
+ * mantissa = buf[10:0]
+ * exponent = buf[15:13 16]
+ */
+ baseline = 12000000 * 32;
+ mantissa = baseline / baud;
+ if (mantissa == 0)
+ mantissa = 1; /* Avoid dividing by zero if baud > 32*12M. */
+ exponent = 0;
+ while (mantissa >= 2048) {
+ if (exponent < 15) {
+ mantissa >>= 1; /* divide by 2 */
+ exponent++;
+ } else {
+ /* Exponent is maxed. Trim mantissa and leave. */
+ mantissa = 2047;
+ break;
+ }
+ }
+
+ buf[3] = 0x80;
+ buf[2] = exponent & 0x01; // LS bit of exponent
+ buf[1] = (exponent & ~0x01) << 4 | mantissa >> 8; // 3 bits of the exponent and MS 3 bits of the mantissa
+ buf[0] = mantissa & 0xff; // LS 8 bits of the mantissa
+
+ /* Calculate and return the exact baud rate. */
+ baud = (baseline / mantissa) >> exponent;
+
+ return baud;
+}
+
+
static void pl2303_encode_baud_rate(struct tty_struct *tty,
struct usb_serial_port *port,
u8 buf[4])
@@ -645,6 +688,8 @@
if (baud == baud_sup)
baud = pl2303_encode_baud_rate_direct(buf, baud);
+ else if (spriv->type->alt_divisors)
+ baud = pl2303_encode_baud_rate_divisor_alt(buf, baud);
else
baud = pl2303_encode_baud_rate_divisor(buf, baud);
next prev parent reply other threads:[~2021-03-13 1:29 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
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 [this message]
2021-03-15 9:07 ` Johan Hovold
2021-03-15 10:07 ` Charles Yeh
2021-03-15 10:24 ` Johan Hovold
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=a475110e-2f44-eeca-3cd2-dd946e5abfe7@IEEE.org \
--to=michaelk@ieee.org \
--cc=charles-yeh@prolific.com.tw \
--cc=charlesyeh522@gmail.com \
--cc=jabbott@rollanet.org \
--cc=johan@kernel.org \
--cc=linux-serial@vger.kernel.org \
--cc=linux-usb@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).