Oops, thank you. I had fixed that but forgot to update my mail before sending
...
Diff:
- for (int i = 0; i < 10000; i++) {
+ for (int i = 0; i < 10000; ) {
On Fri, 2021-07-23 at 11:22 -0400, Michael Plante wrote:
> Haven't studied your full email, but every third sample in your for loop is
> uninitialized.
>
> On Tue, Jul 20, 2021, 1:30 PM Michael Niewöhner <foss@xxxxxxxxxxxxxx> wrote:
> > Hi there!
> >
> > I'm having issues with setting the baudrate/frequency in bitbang mode.
> >
> > First a general question on `ftdi_set_baudrate`. I wonder what the reason is
> > that libftdi multiplies the baudrate by 4 in bitbang mode. I couldn't find
> > any
> > reasons for that in the datasheet, but I might have just missed something.
> >
> > For my actual issue, let's have a look at some code:
> >
> > ```
> > // usual ftdi open and setup
> > // ...
> >
> > // bitbang buffer generation
> > uint8_t *wave = malloc(10000);
> > for (int i = 0; i < 10000; i++) {
> > wave[i++] = 0x00;
> > wave[i++] = 0x01;
> > }
> >
> > ftdi_set_bitmode(ftdi, 0xff, BITMODE_RESET);
> > ftdi_set_baudrate(ftdi, 200000);
> > ftdi_set_bitmode(ftdi, 0x01, BITMODE_BITBANG);
> > ftdi_write_data(ftdi, wave, 10000);
> > ```
> >
> > The resulting waveform should have a frequency of 100kHz (200000 baud / 2
> > bits
> > per full cycle). However, my logic analyzer shows 500kHz. Setting the
> > baudrate
> > after mode setup, leads to 2 MHz - that's what I described in my initial
> > question (freq * 4). Still, the frequency is 5 times higher than expected.
> >
> > For comparison, I have tested this with pyftdi:
> >
> > ```
> > from pyftdi.gpio import GpioAsyncController
> > g = GpioAsyncController()
> > g.configure("ftdi://ftdi:4232/2", direction=0xff)
> > g.ftdi.reset()
> > g.set_frequency(200000)
> > g.write(b'\x00\x01' * 5000)
> > ```
> >
> > This time I measure 100kHz!
> >
> > I had a look at the different implementations for divisor calculations. One
> > difference is, that pyftdi makes use of the /5 divisor in -H ftdis. Also, I
> > get
> > different divisor values but I have not yet compared the calculation yet
> > (but
> > I
> > saw that they differ):
> >
> > baudrate libftdi1 pyftdi
> > 1000 b= 1000, v=12000, i=514 b= 992, v=64771, i= 2
> > 40000 b= 40000, v= 300, i=514 b= 40000, v= 1500, i=514
> > 100000 b=100000, v= 120, i=514 b=100000, v= 600, i=514
> > 200000 b=200000, v= 60, i=514 b=200000, v= 300, i=514
> > 800000 b=800000, v= 15, i=514 b=800000, v= 75, i=514
> >
> > b = resulting baudrate
> > v = value
> > i = index
> >
> > In most cases (except 1000 Hz for example, that could be optimized in
> > pyftdi),
> > the `value` is 5 times higher for pyftdi. I'm not yet sure, what that means
> > exactly, since I haven't fully understood the calculations, yet.
> >
> > Any ideas, what could be wrong here?
> >
> >
> >
> > Michael
> >
> >
> > --
> > libftdi - see http://www.intra2net.com/en/developer/libftdi for details.
> > To unsubscribe send a mail to libftdi+unsubscribe@xxxxxxxxxxxxxxxxxxxxxxx
> >
>
>
> libftdi - see http://www.intra2net.com/en/developer/libftdi for details.
> To unsubscribe send a mail to libftdi+unsubscribe@xxxxxxxxxxxxxxxxxxxxxxx
>
--
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