Re: non-standard baud rates with Prolific 2303 USB-serial

From: Charles Yeh <charlesyeh522@gmail.com>
To: Johan Hovold <johan@kernel.org>
Cc: "Michael G. Katzmann" <michaelk@ieee.org>,
	"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: Wed, 24 Feb 2021 15:34:43 +0800	[thread overview]
Message-ID: <CAAZvQQ6F=cQ-EhC0kgeTVM3GrtBWR+HfM6UJWj2AEF1NYZ-vAQ@mail.gmail.com> (raw)
In-Reply-To: <YDUysZY90FfVhrHK@hovoldconsulting.com>

PL2303HXD
          ===>Device Descriptor<===
bLength:                           0x12
bDescriptorType:                   0x01
bcdUSB:                          0x0110
bDeviceClass:                      0x00  -> This is an Interface Class
Defined Device
bDeviceSubClass:                   0x00
bDeviceProtocol:                   0x00
bMaxPacketSize0:                   0x40 = (64) Bytes
idVendor:                        0x067B = Prolific Technology, Inc.
idProduct:                       0x2303
bcdDevice:                       0x0400


PL2303TA
          ===>Device Descriptor<===
bLength:                           0x12
bDescriptorType:                   0x01
bcdUSB:                          0x0200
bDeviceClass:                      0x00  -> This is an Interface Class
Defined Device
bDeviceSubClass:                   0x00
bDeviceProtocol:                   0x00
bMaxPacketSize0:                   0x40 = (64) Bytes
idVendor:                        0x067B = Prolific Technology, Inc.
idProduct:                       0x2303
bcdDevice:                       0x0300


PL2303HX(A)/XA ( EOL : PHASED OUT SINCE 2012 )
          ===>Device Descriptor<===
bLength:                           0x12
bDescriptorType:                   0x01
bcdUSB:                          0x0110
bDeviceClass:                      0x00  -> This is an Interface Class
Defined Device
bDeviceSubClass:                   0x00
bDeviceProtocol:                   0x00
bMaxPacketSize0:                   0x40 = (64) Bytes
idVendor:                        0x067B = Prolific Technology, Inc.
idProduct:                       0x2303
bcdDevice:                       0x0300


You can use the two fields bcdUSB & bcdDevice to distinguish PL2303HXD
/ PL2303TA / PL2303HX(A)/XA

Johan Hovold <johan@kernel.org> 於 2021年2月24日 週三 上午12:51寫道：
>
> On Tue, Feb 23, 2021 at 11:30:41AM -0500, Michael G. Katzmann wrote:
> > On 2/23/21 11:14 AM, Johan Hovold wrote:
> > > I only have an HXD (and a GC) here.
> > >
> > > The HXD has bcdUSB as 1.10 unlike your TA with 2.00, but not sure that
> > > helps.
> >
> > Sound promising .. why do you think this is this not reliable?
>
> Perhaps it is. Perhaps even bcdDevice of 3.00 is enough (includes some
> older variants that the TA replaced supposedly). Not sure anyone ever
> tried the current scheme on those older models.
>
> Charles, could you post the output of "lsusb -v" for your PL2303TA? And
> did you verify that you actually got 110 Bd with the current Linux
> driver?
>
> Johan