On Thu, Jan 13, 2022 at 8:19 AM Petro Karashchenko < petro.karashche...@gmail.com> wrote:
> Hi, > > I've been working to add SAMv7 Qencoder interface and see that Qencoder > driver expects QEIOC_POSITION to be int32_t value. The issue is that SAMv7 > has 16 bit timer counter interface and the SW extension to 32 bits (by > adding adding or subtracting UINT16_MAX+1 when counter matches 0xffff) does > not seems to work reliably because sometimes pulses are incremented / > decremented not by 1 by the HW. > > The question that I have is whether the Qencder position is expected to > count to negative values "INT16_MIN, ..., -2, -1, 0, 1, 2, .. INT16_MAX" or > position can be in range "0 ... UINT16_MAX" or there are not strict > requirements? > > Best regards, > Petro Correct; you can't rely on that. > I don't know at the moment whether the position is expected to be signed or unsigned, but I have code somewhere to extend precision from 16 bit to 32 bit. If I remember correctly it always saves the previous reading. Each time it samples the encoder it subtracts the old from the new. If > 0x7fff it subtracts the complement, otherwise it adds the value, to a 32-bit variable, which is used as the counter. Let me know if you need me to find the code. Hope this helps, Nathan
