>>>>> "Thomas" == Thomas Jarosch <thomas.jarosch@xxxxxxxxxxxxx> writes:
Thomas> Hi Uwe, On Friday, 2. September 2011 16:49:00 Uwe Bonnes wrote:
>> The other basic is how this bits get stuffed in the USB request. I
>> didn't find any documentation about it. AN_120 is not explicit. Have
>> you more information?
>>
>> I wrote the code with a strong look at the corresponding calculations
>> in /usr/src/linux/drivers/usb/serial/ftdi_sio.c and a test with the
>> scope. For the cases I tested, I saw somehow sensible
>> results. However with the RS232 pattern you can't easily measure
>> exact frequency with the scope.
>>
>> What are your doubts? A slight misscalcuation and bad rounding in my
>> code or values really far off the set value. The last case I can
>> easily test with the scope. Perhaps tell the setting that you expect
>> a bigg error. It is quite easy to test now with examples/serial.
Thomas> Some (lower) baud rates get rounded and I can easily adjust the
Thomas> unit test for that.
Where are your reference values from?
Thomas> For some chips the data written to "value" and "index" changes a
Thomas> lot. I'll come up with examples in the afternoon.
One fractional bit is at 0x100 of index. The other fractional bits are
0x8000 and 0x4000 of value. So a small change in baudrate might cause huge
changes in index/value
Thomas> If you can aknowledge me that the written USB data looks sane,
Thomas> I'm willing to accept the patch even though I can't verify it
Thomas> myself.
Perhaps the unit test should look at devisor, fractional bit and clock
pre-divider separate.
Divisor = value & 0x3ff
Encoded Fractional bits = (index & 0x100)?4:0 + value >>12
clk = (index & 0x100)? 120 MHz: 48 MHz
Then difference get more readable.
--
Uwe Bonnes bon@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Institut fuer Kernphysik Schlossgartenstrasse 9 64289 Darmstadt
--------- Tel. 06151 162516 -------- Fax. 06151 164321 ----------
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