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 <f...@mniewoehner.de> 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
>
>
> --
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>
>
>
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