[avr-gcc-list] Re: USART - Interrupt - problem -Similar

[Steve]

Matthew, Christian,

Thanks for the advice.

>Jolly good (I assume "constantly" means no more often than it should).

Constantly means every time that a character has been sent :)

I would of course use bit masks in an application, the purpose of the
code was just to understand the UART interrupts. However I was not aware
of the _BV macro for this. Therefore thanks for pointing me to this.

Steve


On Monday 24 May 2004 7:53 pm, Steve wrote:
> Matthew,
>
> I followed your advise and now have the transmit complete interrupt
> firing constantly.

Jolly good (I assume "constantly" means no more often than it should).

>Just quickly incase it helps someone else; I changed
> the interrupt code to the following:
>
> /*UDRE data register empty*/
> SIGNAL(SIG_UART_DATA)
> {
>       UCR = 0xD8; //disable this int
> }

It's a really good idea to use the _BV macro and the predefined bits for
this 
sort of thing (and it's probably not a good idea to set all the bits,
you 
would be better off using a mask) ie:

UCR &= ~_BV(UDRIE);

It's clearer, and also not all AVRs have the same bits in the same
places.

Cheers,

Matthew.

------------------------------

Date: Tue, 25 May 2004 00:14:48 +0100
From: Christian Ludlam <address@hidden>
To: address@hidden
Subject: Re: [avr-gcc-list] Re: Re: USART - Interrupt - problem -Similar
        (SOLVED)
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In-Reply-To: <address@hidden>
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Message: 5

On 24 May Matthew Arcus wrote:

> On Monday 24 May 2004 7:53 pm, Steve wrote:
> >Just quickly incase it helps someone else; I changed the interrupt
code to
> >the following:
> >
> > /*UDRE data register empty*/
> > SIGNAL(SIG_UART_DATA)
> > {
> >     UCR = 0xD8; //disable this int
> > }
> 
> It's a really good idea to use the _BV macro and the predefined bits
for
> this  sort of thing (and it's probably not a good idea to set all the
bits,
> you  would be better off using a mask) ie:
> 
> UCR &= ~_BV(UDRIE);
> 
> It's clearer, and also not all AVRs have the same bits in the same
places.

In this case it's more efficient too, since the compiler can use the cbi
instruction (saving a register and a cycle).

-- 
Christian Ludlam
address@hidden

------------------------------

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