Question regarding ns16550

[Daniel Gutson]

On Fri, Oct 24, 2014 at 2:16 PM, Daniel Gutson
<daniel.gutson at tallertechnologies.com> wrote:
> On Fri, Oct 24, 2014 at 2:33 AM, Sebastian Huber
> <sebastian.huber at embedded-brains.de> wrote:
>> On 23/10/14 18:12, Daniel Gutson wrote:
>>>
>>> On Thu, Oct 23, 2014 at 5:47 AM, Sebastian Huber
>>> <sebastian.huber at embedded-brains.de>  wrote:
>>>>
>>>> >Hello Daniel,
>>>
>>> Hi Sebastian,
>>>
>>>> >
>>>> >I never notice a problem with this driver.  It should only write to the
>>>> > FIFO
>>>> >in case it is completely empty.  Did you observe problems?
>>>
>>> no, I didn't (actually I found this while looking for a serial bug
>>> which turned out to be due
>>> to a different cause).
>>> However, I notice that this isn't like what the polling write does (of
>>> course I'm not talking
>>> about the polling/interrput difference, but when writing byte-per-byte
>>> to the FIFO, I think
>>> both methods should do the same).
>>> IOW, what happens if the 'for' loop is too fast for the device? Will
>>> the latter be able to
>>> put the char in the FIFO and be ready for the next one? Isn't
>>> SP_LSR_THOLD exactly
>>> to tell whether the device' FIFO is ready to accept the next byte?
>>> Writing to the FIFO when it's completely empty is not the problem I
>>> see since it is
>>> guaranteed by the interrupt. My concern is different: it's whether the
>>> FIFO is filled too fast
>>> for the device.
>>>
>>>
>>
>> Its not clear to me from the documentation if this is really necessary.  I
>> never noticed problems on several targets with this driver.

FWIW, we asked TI about this:
http://e2e.ti.com/support/arm/sitara_arm/f/791/p/378177/1331822.aspx#1331822
In short: they explained that the register is not needed when in FIFO
mode, which is the case (but it is needed when writing byte-per-byte).

   Daniel.

>
> Ok.
>
>>
>>
>> --
>> Sebastian Huber, embedded brains GmbH
>>
>> Address : Dornierstr. 4, D-82178 Puchheim, Germany
>> Phone   : +49 89 189 47 41-16
>> Fax     : +49 89 189 47 41-09
>> E-Mail  : sebastian.huber at embedded-brains.de
>> PGP     : Public key available on request.
>>
>> Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.
>
>
>
> --
>
> Daniel F. Gutson
> Chief Engineering Officer, SPD
>
>
> San Lorenzo 47, 3rd Floor, Office 5
>
> Córdoba, Argentina
>
>
> Phone: +54 351 4217888 / +54 351 4218211
>
> Skype: dgutson



-- 

Daniel F. Gutson
Chief Engineering Officer, SPD


San Lorenzo 47, 3rd Floor, Office 5

Córdoba, Argentina


Phone: +54 351 4217888 / +54 351 4218211

Skype: dgutson