On 3/5/21 4:36 AM, Johan Hovold wrote:

On Fri, Mar 05, 2021 at 05:32:23PM +0800, Charles Yeh wrote:

quoted

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.

quoted

Johan Hovold [off-list ref] 於 2021年2月25日 週四 上午1:00寫道：

quoted

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;
}