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

From: "Michael G. Katzmann" <michaelk@IEEE.org>
To: Johan Hovold <johan@kernel.org>
Cc: charles-yeh@prolific.com.tw, linux-serial@vger.kernel.org,
	linux-usb@vger.kernel.org, Charles Yeh <charlesyeh522@gmail.com>,
	Joe Abbott <jabbott@rollanet.org>
Subject: Re: non-standard baud rates with Prolific 2303 USB-serial
Date: Tue, 23 Feb 2021 09:58:47 -0500	[thread overview]
Message-ID: <780b9aa6-890d-47fd-d6b2-cd9a39f7634a@IEEE.org> (raw)
In-Reply-To: <YDPS3AP63/PwmwJU@hovoldconsulting.com>

On 2/22/21 10:50 AM, Johan Hovold wrote:

Well I found I have another Prolific device here that I got from Adafruit (https://www.adafruit.com/product/954)

It also has a Prolific 2303 and behaves exactly like the other one. i.e. with the current Linux driver it gives a very high baudrate when set to 110 bd and gives 110bd when the modifications are made to the driver that I found.

Is it that we are presuming that what Prolific is telling us is true and only Joe and I are actually measuring the data rate?  (i.e. why does the Prolific Windows driver set the values as Joe found ???)

Adafruit device:

Bus 001 Device 013: ID 067b:2303 Prolific Technology, Inc. PL2303 Serial Port
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               2.00
  bDeviceClass            0
  bDeviceSubClass         0
  bDeviceProtocol         0
  bMaxPacketSize0        64
  idVendor           0x067b Prolific Technology, Inc.
  idProduct          0x2303 PL2303 Serial Port
  bcdDevice            3.00
  iManufacturer           1 Prolific Technology Inc.
  iProduct                2 USB-Serial Controller
  iSerial                 0
  bNumConfigurations      1
  Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength       0x0027
    bNumInterfaces          1
    bConfigurationValue     1
    iConfiguration          0
    bmAttributes         0xa0
      (Bus Powered)
      Remote Wakeup
    MaxPower              100mA
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        0
      bAlternateSetting       0
      bNumEndpoints           3
      bInterfaceClass       255 Vendor Specific Class
      bInterfaceSubClass      0
      bInterfaceProtocol      0
      iInterface              0
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x81  EP 1 IN
        bmAttributes            3
          Transfer Type            Interrupt
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x000a  1x 10 bytes
        bInterval               1
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x02  EP 2 OUT
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0040  1x 64 bytes
        bInterval               0
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x83  EP 3 IN
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0040  1x 64 bytes
        bInterval               0

-- 
   |\      _,,,---,,_             Michael Katzmann
   /,`.-'`'    -.  ;-;;,_         NV3Z / VK2BEA / G4NYV
  |,4-  ) )-,_. ,\ (  `'-' 
 '---''(_/--'  `-'\_)             MichaelK@IEEE.org