Allwinner H3 UART speed 250000 bps ?

[asdf...@gmail.com]

I am experiencing issues with Allwinner H3's UART. Trying to use it @ 250000 bps, but unable to established reliable communication. It works fine up to 150000 bps, but above this speed no proper communication. I tried Armbian with 4.14.65 and 4.13 Linux kernels.

[Arjan van Vught]

This 250000 is similar to DMX. And from a baremetal programming point of view I can tell that is speed is working fine on H2+/H3 (http://www.raspberrypi-dmx.org/allwinner-h3)

- Arjan

[Jernej Škrabec]

Dne sreda, 12. september 2018 ob 18:16:45 CEST je asdf...@gmail.com
napisal(a):

Currently, with 24 MHz clock parent, 1.5 Mbps is the highest possible rate (24
MHz / 16 / x, where x is integer number). Theoretically, it is possible to
change clock parent but I'm not sure anyone actually tried that. Such change
would also affect I2C IIRC.

Best regards,
Jernej

[Arjan van Vught]

Op donderdag 13 september 2018 16:35:22 UTC+2 schreef Jernej Skrabec:

With baudrate = 24000000 / 16 / x = 250000, then x =  6 (UART_DLH=6, UART_DLL=0)

So with the F_24M the requested 250000 is doable. No need to change clock parent.

- Arjan

[Jernej Škrabec]

Dne četrtek, 13. september 2018 ob 17:35:32 CEST je Arjan van Vught
napisal(a):

> Op donderdag 13 september 2018 16:35:22 UTC+2 schreef Jernej Skrabec:
> > Dne sreda, 12. september 2018 ob 18:16:45 CEST je asdf...@gmail.com

> > <javascript:>

> >
> > napisal(a):
> > > I am experiencing issues with Allwinner H3's UART. Trying to use it @
> > > 250000 bps, but unable to established reliable communication. It works
> >
> > fine
> >
> > > up to 150000 bps, but above this speed no proper communication. I tried
> > > Armbian with 4.14.65 and 4.13 Linux kernels.
> >
> > Currently, with 24 MHz clock parent, 1.5 Mbps is the highest possible rate
> > (24
> > MHz / 16 / x, where x is integer number). Theoretically, it is possible to
> > change clock parent but I'm not sure anyone actually tried that. Such
> > change
> > would also affect I2C IIRC.
> >
> > Best regards,
> > Jernej
> >
> >
> > With baudrate = 24000000 / 16 / x = 250000, then x = 6 (UART_DLH=6,
>
> UART_DLL=0)
> So with the F_24M the requested 250000 is doable. No need to change clock
> parent.

Sorry, I misread. I though 2.5 Mbps is needed.

Best regards,
Jernej

>
> - Arjan

[Maksims Matjakubovs]

 Hello,

 Please check IRC history at http://irclog.whitequark.org/linux-sunxi .
 It's possible to get 2.5Mbps UART speed by changing UART (needed APB) parent clock source to PLL and it frequency to 40Mhz .

 I used V3s UART at speed 12.5Mbps (with parent clock 200Mhz) and it worked normally. 

Best regards,
Maksims