hi, so do you want me make this change? On Wed, 12 Jul 2023 at 10:54, Gedare Bloom <ged...@rtems.org> wrote:
> 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