From: "Albrecht Dreß" <albrecht.dress@arcor•de>
To: grant.likely@secretlab•ca, albrecht.dress@arcor•de
Cc: linuxppc-dev@ozlabs•org
Subject: Re: [Patch v.2] mpc5200b/uart: improve baud rate calculation (reach high baud rates, better accuracy)
Date: Thu, 4 Mar 2010 10:56:46 +0100 (CET) [thread overview]
Message-ID: <16827431.1267696606015.JavaMail.ngmail@webmail13.arcor-online.net> (raw)
In-Reply-To: <fa686aa41003031307j79e004cfk49297e419a65f5da@mail.gmail.com>
Hi Grant:
Thanks a lot for your input!
[snip]
> Save yourself some duplicated code here. The above 14 lines can be
> shared between the 512x, 52xx and 5200b versions. Create yourself an
> internal __mpc5xxx_psc_set_divisor() function that is passed the *psc,
> the divisor, and the clock select register setting (both the 5200 and
> the 5121 have the clock select register).
Hmm, yes, that's true. Will look into that.
[snip]
> > @@ -604,7 +676,6 @@ mpc52xx_uart_set_termios(struct uart_por
> >
> > =A0 =A0 =A0 =A0baud =3D uart_get_baud_rate(port, new, old, 0, port->uar=
tclk/16);
>=20
> I'm probably nitpicking, because I don't know if the io pin will
> handle this speed but uartclk/16 is no longer the maximum baudrate if
> a /4 prescaler is used.
Yes, you are right. Must of course be fixed.
[snip]
> > @@ -635,8 +706,7 @@ mpc52xx_uart_set_termios(struct uart_por
> > =A0 =A0 =A0 =A0out_8(&psc->command, MPC52xx_PSC_SEL_MODE_REG_1);
> > =A0 =A0 =A0 =A0out_8(&psc->mode, mr1);
> > =A0 =A0 =A0 =A0out_8(&psc->mode, mr2);
> > - =A0 =A0 =A0 out_8(&psc->ctur, ctr >> 8);
> > - =A0 =A0 =A0 out_8(&psc->ctlr, ctr & 0xff);
> > + =A0 =A0 =A0 psc_ops->set_divisor(port, quot);
>=20
> Hmmm. The divisor calculations have some tricky bits to them. I
> would consider changing the set_divisor() function to accept a baud
> rate, and modify the set_divisor function to call uart_get_divisor().
That sounds like a good idea to me. I will change the code that way.
> That way each set_divisor() can do whatever makes the most sense for
> the divisors available to it. The 5121 for example has both a /10 and
> a /32 divisor, plus it can use an external clock.
Ouch. I don't have a 512x, but isn't the current code plain wrong then? I=
t uses mpc5xxx_get_bus_frequency() as input for the baud rate calculation, =
and if the serial code assumes /16 instead of /10, the result must be terri=
bly off. Or did I miss something here?
Best, Albrecht.
Tolle Dekollet=E9s oder scharfe Tatoos? Vote jetzt ... oder mach selbst mit=
und zeige Deine Schokoladenseite
bei Topp oder Hopp von Arcor: http://www.arcor.de/rd/footer.toh
next prev parent reply other threads:[~2010-03-04 9:56 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-03-03 18:23 [Patch v.2] mpc5200b/uart: improve baud rate calculation (reach high baud rates, better accuracy) Albrecht Dreß
2010-03-03 21:07 ` Grant Likely
2010-03-04 9:56 ` Albrecht Dreß [this message]
2010-03-04 13:27 ` Grant Likely
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