UART TX FIFO SIZE

Started by Hong Jiang February 25, 2005
Hi all members:

I can get a Rx FIFO depth through FCR register,but how can I calculate the Tx FIFO size.

According to the LPC2119 document,this CPU's UART is compatible with the 16c550's which has a certain Tx FIFO size while I cann't find any words about that in philipse's document.

thanks
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An Engineer's Guide to the LPC2100 Series

At 04:30 PM 2/25/05 +0800, Hong Jiang wrote:

>Hi all members:
>
>I can get a Rx FIFO depth through FCR register,but how can I calculate the
>Tx FIFO size.
>
>According to the LPC2119 document,this CPU's UART is compatible with the
>16c550's which has a certain Tx FIFO size while I cann't find any words
>about that in philipse's document.

The top of page 140 of the user manual "16 byte Receive and Transmit FIFOs."

Robert

" 'Freedom' has no meaning of itself. There are always restrictions,
be they legal, genetic, or physical. If you don't believe me, try to
chew a radio signal. "

Kelvin Throop, III



--- In , Robert Adsett <subscriptions@a...> wrote:
> At 04:30 PM 2/25/05 +0800, Hong Jiang wrote:
>
> >Hi all members:
> >
> >I can get a Rx FIFO depth through FCR register,but how can I
calculate the
> >Tx FIFO size.
> >
> >According to the LPC2119 document,this CPU's UART is compatible
with the
> >16c550's which has a certain Tx FIFO size while I cann't find any
words
> >about that in philipse's document.
>
> The top of page 140 of the user manual "16 byte Receive and Transmit
FIFOs."
>
> Robert
>
> " 'Freedom' has no meaning of itself. There are always restrictions,
> be they legal, genetic, or physical. If you don't believe me, try to
> chew a radio signal. "
>
> Kelvin Throop, III

I just wish they gave you a way to know how many bytes are in the FIFO
(at least the tx fifo). In my drivers I just keep track of how many I
put in, and they when I get THRE I reset the count to zero.

--Peter



At 09:11 PM 2/25/05 +0000, peterburdine wrote:
>I just wish they gave you a way to know how many bytes are in the FIFO
>(at least the tx fifo). In my drivers I just keep track of how many I
>put in, and they when I get THRE I reset the count to zero.

Why? If you are doing a polled transmission I could see the use for a FIFO
full flag but for interrupt driven you can stuff the FIFO faster than you
can remove a byte from it at most baud rates. Even for polled transmission
I don't see much loss of efficiency (if there were you could easily switch
to interrupt driven). I don't see any use for a FIFO count and I've not
seen a UART with a FIFO that has one.

Robert
" 'Freedom' has no meaning of itself. There are always restrictions,
be they legal, genetic, or physical. If you don't believe me, try to
chew a radio signal. "

Kelvin Throop, III



--- In , Robert Adsett <subscriptions@a...> wrote:
> At 09:11 PM 2/25/05 +0000, peterburdine wrote:
> >I just wish they gave you a way to know how many bytes are in the FIFO
> >(at least the tx fifo). In my drivers I just keep track of how many I
> >put in, and they when I get THRE I reset the count to zero.
>
> Why? If you are doing a polled transmission I could see the use for
a FIFO
> full flag but for interrupt driven you can stuff the FIFO faster
than you
> can remove a byte from it at most baud rates. Even for polled
transmission
> I don't see much loss of efficiency (if there were you could easily
switch
> to interrupt driven). I don't see any use for a FIFO count and I've
not
> seen a UART with a FIFO that has one.
>
> Robert >
> " 'Freedom' has no meaning of itself. There are always restrictions,
> be they legal, genetic, or physical. If you don't believe me, try to
> chew a radio signal. "
>
> Kelvin Throop, III

Well thats what I meant to get at, there is no way to tell if it is full.





peterburdine <> wrote:

--- In , Robert Adsett <subscriptions@a...> wrote:
> At 04:30 PM 2/25/05 +0800, Hong Jiang wrote:
>
> >Hi all members:
> >
> >I can get a Rx FIFO depth through FCR register,but how can I
calculate the
> >Tx FIFO size.
> >
> >According to the LPC2119 document,this CPU's UART is compatible
with the
> >16c550's which has a certain Tx FIFO size while I cann't find any
words
> >about that in philipse's document.
>
> The top of page 140 of the user manual "16 byte Receive and Transmit
FIFOs."
>
> Robert
>
> " 'Freedom' has no meaning of itself. There are always restrictions,
> be they legal, genetic, or physical. If you don't believe me, try to
> chew a radio signal. "
>
> Kelvin Throop, III

I just wish they gave you a way to know how many bytes are in the FIFO
(at least the tx fifo). In my drivers I just keep track of how many I
put in, and they when I get THRE I reset the count to zero.

--Peter

peterburdine:

Thanks a lot!I'm too careless to find the Tx FIFO size.

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