auxdisplay: hd44780: move cursor home after clear display command

  From: Hugo Villeneuve <hvilleneuve@dimonoff.com>

The "clear display" command on the NewHaven NHD-0220DZW-AG5 display
does NOT change the DDRAM address to 00h (home position) like the
standard Hitachi HD44780 controller. As a consequence, the starting
position of the initial string LCD_INIT_TEXT is not guaranteed to be
at 0,0 depending on where the cursor was before the clear display
command.

Extract of CLEAR_DISPLAY command from datasheets of:

    Hitachi HD44780:
        ... It then sets DDRAM address 0 into the address counter...

    NewHaven NHD-0220DZW-AG5 datasheet:
	... This instruction does not change the DDRAM Address

Move the cursor home after sending clear display command to support
non-standard LCDs.

Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
---
 drivers/auxdisplay/hd44780_common.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)


base-commit: c17414a273b81fe4e34e11d69fc30cc8b1431614
  

On Thu, Jul 6, 2023 at 8:51 PM Hugo Villeneuve <hugo@hugovil.com> wrote:
>
> The "clear display" command on the NewHaven NHD-0220DZW-AG5 display
> does NOT change the DDRAM address to 00h (home position) like the
> standard Hitachi HD44780 controller. As a consequence, the starting
> position of the initial string LCD_INIT_TEXT is not guaranteed to be
> at 0,0 depending on where the cursor was before the clear display
> command.
>
> Extract of CLEAR_DISPLAY command from datasheets of:
>
>     Hitachi HD44780:
>         ... It then sets DDRAM address 0 into the address counter...
>
>     NewHaven NHD-0220DZW-AG5 datasheet:
>         ... This instruction does not change the DDRAM Address
>
> Move the cursor home after sending clear display command to support
> non-standard LCDs.
>
> Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>

Thanks! Sounds good to me, as long the extra command does not
introduce some issue with the actual HD44780 -- can we double-check
the HD44780 still works as expected?

Cc'ing Lars and Geert since they may be able to give it a quick test.

> +       /*
> +        * Some LCDs (ex: NewHaven) do not reset the DDRAM address when
> +        * executing the CLEAR_DISPLAY command. Explicitely move cursor
> +        * to home position to account for these non-standard LCDs:
> +        */
> +       return hd44780_common_home(lcd);

Few nits:

  - Explicitely -> Explicitly.
  - Isn't the command `DISPLAY_CLEAR` instead of `CLEAR_DISPLAY`? (at
least the identifier above is `LCD_CMD_DISPLAY_CLEAR`).
  - `:` -> `.`.

What about something like:

    The Hitachi HD44780 controller (and compatible ones) reset the
DDRAM address when executing the `DISPLAY_CLEAR` command, thus the
following call is not required. However, other controllers do not
(e.g. NewHaven NHD-0220DZW-AG5), thus move the cursor to home
unconditionally to support both.

Cheers,
Miguel
  

On Thu, 6 Jul 2023 21:33:05 +0200
Miguel Ojeda <miguel.ojeda.sandonis@gmail.com> wrote:

> On Thu, Jul 6, 2023 at 8:51 PM Hugo Villeneuve <hugo@hugovil.com> wrote:
> >
> > The "clear display" command on the NewHaven NHD-0220DZW-AG5 display
> > does NOT change the DDRAM address to 00h (home position) like the
> > standard Hitachi HD44780 controller. As a consequence, the starting
> > position of the initial string LCD_INIT_TEXT is not guaranteed to be
> > at 0,0 depending on where the cursor was before the clear display
> > command.
> >
> > Extract of CLEAR_DISPLAY command from datasheets of:
> >
> >     Hitachi HD44780:
> >         ... It then sets DDRAM address 0 into the address counter...
> >
> >     NewHaven NHD-0220DZW-AG5 datasheet:
> >         ... This instruction does not change the DDRAM Address
> >
> > Move the cursor home after sending clear display command to support
> > non-standard LCDs.
> >
> > Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
> 
> Thanks! Sounds good to me, as long the extra command does not
> introduce some issue with the actual HD44780 -- can we double-check
> the HD44780 still works as expected?
> 
> Cc'ing Lars and Geert since they may be able to give it a quick test.

Hi Miguel,
I do not have a standard Hitachi controller to test it on, so lets wait
for feedback from Lars and Geert or others.

> > +       /*
> > +        * Some LCDs (ex: NewHaven) do not reset the DDRAM address when
> > +        * executing the CLEAR_DISPLAY command. Explicitely move cursor
> > +        * to home position to account for these non-standard LCDs:
> > +        */
> > +       return hd44780_common_home(lcd);
> 
> Few nits:
> 
>   - Explicitely -> Explicitly.
>   - Isn't the command `DISPLAY_CLEAR` instead of `CLEAR_DISPLAY`? (at
> least the identifier above is `LCD_CMD_DISPLAY_CLEAR`).

Yes, I have also modified the commit log message to be consistent with
the code.

>   - `:` -> `.`.
> What about something like:
> 
>     The Hitachi HD44780 controller (and compatible ones) reset the
> DDRAM address when executing the `DISPLAY_CLEAR` command, thus the
> following call is not required. However, other controllers do not
> (e.g. NewHaven NHD-0220DZW-AG5), thus move the cursor to home
> unconditionally to support both.

Ok, changed comments to that.

Thank you,
Hugo.
  

Am 2023-07-06 21:49, schrieb Hugo Villeneuve:
> On Thu, 6 Jul 2023 21:33:05 +0200
> Miguel Ojeda <miguel.ojeda.sandonis@gmail.com> wrote:
> 
>> On Thu, Jul 6, 2023 at 8:51 PM Hugo Villeneuve <hugo@hugovil.com> 
>> wrote:
>> >
>> > The "clear display" command on the NewHaven NHD-0220DZW-AG5 display
>> > does NOT change the DDRAM address to 00h (home position) like the
>> > standard Hitachi HD44780 controller. As a consequence, the starting
>> > position of the initial string LCD_INIT_TEXT is not guaranteed to be
>> > at 0,0 depending on where the cursor was before the clear display
>> > command.
>> >
>> > Extract of CLEAR_DISPLAY command from datasheets of:
>> >
>> >     Hitachi HD44780:
>> >         ... It then sets DDRAM address 0 into the address counter...
>> >
>> >     NewHaven NHD-0220DZW-AG5 datasheet:
>> >         ... This instruction does not change the DDRAM Address
>> >
>> > Move the cursor home after sending clear display command to support
>> > non-standard LCDs.
>> >
>> > Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
>> 
>> Thanks! Sounds good to me, as long the extra command does not
>> introduce some issue with the actual HD44780 -- can we double-check
>> the HD44780 still works as expected?
>> 
>> Cc'ing Lars and Geert since they may be able to give it a quick test.
> 
> Hi Miguel,
> I do not have a standard Hitachi controller to test it on, so lets wait
> for feedback from Lars and Geert or others.

Sorry guys,
I do not have access to the relevant hardware anymore. I am CC'ing 
Christian,
who has the relevant hardware and maybe he can help testing the patch.
Christian is on vacation up until mid august, so we have to wait a bit 
more
for someone able to test this.

BTW: The displays I did the work back then on were for sure not genuine
Hitachi ones either.
I do not see, that the little patch should do any harm.

Regards,
Lars
  

poeschel@lemonage.de writes:

> Am 2023-07-06 21:49, schrieb Hugo Villeneuve:
>> On Thu, 6 Jul 2023 21:33:05 +0200
>> Miguel Ojeda <miguel.ojeda.sandonis@gmail.com> wrote:
>>
>>> On Thu, Jul 6, 2023 at 8:51 PM Hugo Villeneuve <hugo@hugovil.com> wrote:
>>> >
>>> > The "clear display" command on the NewHaven NHD-0220DZW-AG5 display
>>> > does NOT change the DDRAM address to 00h (home position) like the
>>> > standard Hitachi HD44780 controller. As a consequence, the starting
>>> > position of the initial string LCD_INIT_TEXT is not guaranteed to be
>>> > at 0,0 depending on where the cursor was before the clear display
>>> > command.
>>> >
>>> > Extract of CLEAR_DISPLAY command from datasheets of:
>>> >
>>> >     Hitachi HD44780:
>>> >         ... It then sets DDRAM address 0 into the address counter...
>>> >
>>> >     NewHaven NHD-0220DZW-AG5 datasheet:
>>> >         ... This instruction does not change the DDRAM Address
>>> >
>>> > Move the cursor home after sending clear display command to support
>>> > non-standard LCDs.
>>> >
>>> > Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
>>> Thanks! Sounds good to me, as long the extra command does not
>>> introduce some issue with the actual HD44780 -- can we double-check
>>> the HD44780 still works as expected?
>>> Cc'ing Lars and Geert since they may be able to give it a quick test.
>> Hi Miguel,
>> I do not have a standard Hitachi controller to test it on, so lets wait
>> for feedback from Lars and Geert or others.
>
> Sorry guys,
> I do not have access to the relevant hardware anymore. I am CC'ing Christian,
> who has the relevant hardware and maybe he can help testing the patch.
> Christian is on vacation up until mid august, so we have to wait a bit more
> for someone able to test this.
>
> BTW: The displays I did the work back then on were for sure not genuine
> Hitachi ones either.
> I do not see, that the little patch should do any harm.
>
> Regards,
> Lars


I was actually hooking up a 16x2 HD44780 on my BeagleBone Black last
night before I came across this patch, so I was able to test this. It
works fine for me. I tested with:

    $ printf '\f' > /dev/lcd
    $ printf 'Hello\nWorld!\n' > /dev/lcd
    $ printf '\x1b[LR' > /dev/lcd
    $ printf '\x1b[LR' > /dev/lcd
    $ printf '\x1b[LR' > /dev/lcd
    $ printf '\f' > /dev/lcd
    $ printf 'Goodbye\nWorld!\n' > /dev/lcd

As expected, "Goodbye World!" was correctly placed left-aligned on the
display, split over both lines. Let me know if there is something else
you would like me to do to test this!

Tested-by: David Reaver <me@davidreaver.com>
  

On Sat, Jul 22, 2023 at 4:54 PM David Reaver <me@davidreaver.com> wrote:
>
> I was actually hooking up a 16x2 HD44780 on my BeagleBone Black last
> night before I came across this patch, so I was able to test this. It
> works fine for me. I tested with:
>
>     $ printf '\f' > /dev/lcd
>     $ printf 'Hello\nWorld!\n' > /dev/lcd
>     $ printf '\x1b[LR' > /dev/lcd
>     $ printf '\x1b[LR' > /dev/lcd
>     $ printf '\x1b[LR' > /dev/lcd
>     $ printf '\f' > /dev/lcd
>     $ printf 'Goodbye\nWorld!\n' > /dev/lcd
>
> As expected, "Goodbye World!" was correctly placed left-aligned on the
> display, split over both lines. Let me know if there is something else
> you would like me to do to test this!
>
> Tested-by: David Reaver <me@davidreaver.com>

Thanks a lot, that is very helpful!

I will wait a while in case Christian or somebody else wants to test
it, and send it for 6.6.

Cheers,
Miguel
  

On Sat, 22 Jul 2023 18:04:03 +0200
Miguel Ojeda <miguel.ojeda.sandonis@gmail.com> wrote:

> On Sat, Jul 22, 2023 at 4:54 PM David Reaver <me@davidreaver.com> wrote:
> >
> > I was actually hooking up a 16x2 HD44780 on my BeagleBone Black last
> > night before I came across this patch, so I was able to test this. It
> > works fine for me. I tested with:
> >
> >     $ printf '\f' > /dev/lcd
> >     $ printf 'Hello\nWorld!\n' > /dev/lcd
> >     $ printf '\x1b[LR' > /dev/lcd
> >     $ printf '\x1b[LR' > /dev/lcd
> >     $ printf '\x1b[LR' > /dev/lcd
> >     $ printf '\f' > /dev/lcd
> >     $ printf 'Goodbye\nWorld!\n' > /dev/lcd
> >
> > As expected, "Goodbye World!" was correctly placed left-aligned on the
> > display, split over both lines. Let me know if there is something else
> > you would like me to do to test this!
> >
> > Tested-by: David Reaver <me@davidreaver.com>
> 
> Thanks a lot, that is very helpful!
> 
> I will wait a while in case Christian or somebody else wants to test
> it, and send it for 6.6.

Hi Miguel,
in the meantime, I will send V2 of the patch with the changes you
suggested for the commit message and the comments.

Hugo.