On Wed, Jul 12, 2023 at 8:06 AM Joel Sherrill <j...@rtems.org> wrote: > > > Pavel this was filed as https://devel.rtems.org/ticket/4903. The ticket > submitter > didn't give a patch, just a code change snippet and explanation. Zack turned > it into > a patch. You will need to post that on the ticket to get the submitter's > feedback. > > I hope you don't mind copying that to the ticket and seeing what you think is > really up. > I posted it over there. Thanks Pavel and Joel.
> Thanks. > > --joel > > On Wed, Jul 12, 2023 at 8:49 AM Pavel Pisa <ppisa4li...@pikron.com> wrote: >> >> Hello Zack and Gedare, >> >> On Tuesday 11 of July 2023 19:52:27 Gedare Bloom wrote: >> > Thanks for the patch. Someone should probably test it, or identify in >> > the documentation why this calculation was off-by-1. Pavel, any clues? >> > On Sun, Jul 9, 2023 at 10:09 PM zack <zakthertems...@gmail.com> wrote: >> > > Fixes #4903 >> > > diff --git a/bsps/arm/tms570/console/tms570-sci.c >> > > b/bsps/arm/tms570/console/tms570-sci.c index 768770a4c8..59a0b7e6f1 >> > > 100644 >> > > --- a/bsps/arm/tms570/console/tms570-sci.c >> > > +++ b/bsps/arm/tms570/console/tms570-sci.c >> > > @@ -311,7 +311,7 @@ bool tms570_sci_set_attributes( >> > > /* Apply baudrate to the hardware */ >> > > baudrate *= 2 * 16; >> > > bauddiv = (BSP_PLL_OUT_CLOCK + baudrate / 2) / baudrate; >> > > - ctx->regs->BRS = bauddiv? bauddiv - 1: 0; >> > > + ctx->regs->BRS = bauddiv? bauddiv - 2: 0; >> >> I think that change is not correct. The actual used values >> for BSP_PLL_OUT_CLOCK and baudrate should be provided to analyze >> the case. The code can result in some rounding error and can >> be enhanced if fractional divider is used or even super finegrained >> fractional divider. But these options are available only for >> for SCI/LIN peripheral case. >> >> According to >> >> TMS570LS31x/21x 16/32-Bit RISC Flash Microcontroller >> Technical Reference Manual >> Literature Number: SPNU499B >> >> 26.2.3 SCI Baud Rate >> >> SCICLK Frequency = VCLK Frequency / (P + 1 + M / 16) >> >> Asynchronous baud value = SCICLK Frequency / 16 >> >> So the substraction of one corresponds to the manual. >> >> Actual code does not use M part. It would be problem if it is >> leftover from some boot/monitor but it is part of BRS 32-bit >> register which is overwritten in the whole, so such problem >> should not appear either. >> >> So I vote against the proposed change for now and suggest >> to do analysis what happens in the computation and what >> are input values and output. Change would/could affect >> negatively large number of combinations of the baudrate >> and clocks. >> >> I would consider to discuss if the rounding formula >> could/should be updated, but I think that it is the best >> which cane be achieved for rations which do not result >> in exact ratio. >> >> (BSP_PLL_OUT_CLOCK + baudrate / 2) / baudrate; >> >> If there is interrest then code can be enhanced by fraction >> dividers for SCI/LIN peripheral case. The field with variant >> should be added into tms570_sci_context and in this case >> the alternative formula can be used >> >> long long bauddiv; >> bauddiv = (BSP_PLL_OUT_CLOCK * 16ll + baudrate / 2) / baudrate; >> ctx->regs->BRS = ((bauddiv >> 4) & 0xffffff) | ((bauddiv & 0xf) << 24); >> >> which should be rewritten after header for SCI/LIN update to >> >> ctx->regs->BRS = TMS570_LIN_BRS_P(bauddiv >> 4) | TMS570_LIN_BRS_M(bauddiv >> & 0xf); > > > >> >> >> Best wishes, >> >> >> Pavel >> -- >> Pavel Pisa >> phone: +420 603531357 >> e-mail: p...@cmp.felk.cvut.cz >> Department of Control Engineering FEE CVUT >> Karlovo namesti 13, 121 35, Prague 2 >> university: http://control.fel.cvut.cz/ >> personal: http://cmp.felk.cvut.cz/~pisa >> projects: https://www.openhub.net/accounts/ppisa >> CAN related:http://canbus.pages.fel.cvut.cz/ >> RISC-V education: https://comparch.edu.cvut.cz/ >> Open Technologies Research Education and Exchange Services >> https://gitlab.fel.cvut.cz/otrees/org/-/wikis/home >> >> _______________________________________________ >> devel mailing list >> devel@rtems.org >> http://lists.rtems.org/mailman/listinfo/devel _______________________________________________ devel mailing list devel@rtems.org http://lists.rtems.org/mailman/listinfo/devel
