Nucleus PLUS sdc.c usart tx buffer seems always full

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posted
16 years ago

Thu, Jun 14, 2007 11:24 AM

We have a case where we 1) some times loose send character on the usart and now 2) Nucleus _always_ sees a full tx buffer (after sending a "random" number of characters first - several KB) and does a NU_Sleep(1) in a loop forever. This seems to hog the machine. We have sdc.c version "Nucleus PLUS\Integrator\RVCT 1.15.17" and run on for ARM9.

If this is,a s I presume, an sdc.c error - does anybody have a fix for this?

It seems like the TX interrupt has been switched off, or a skew or a glitch in the code may have handled the "while (uart->tx_buffer_write =3D=3D uart->tx_buffer_read)" idices incorrectly. They never change.

=D8yvind Teig Autronica Fire and Security AS A UTC Fire & Security Company

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posted
16 years ago

Thu, Jun 14, 2007 12:31 PM

Comment from the inititator of this thread:

If I add a cnt, so that our Nucleus task does not any more block on full TX buffer, brute force like this, then.. /* If the buffer is full wait for it to empty a little. */ UINT8 cnt=3D0; // oyviteig while ((uart->tx_buffer_write =3D=3D uart->tx_buffer_read) && (cnttx_buffer_read =3D uart->tx_buffer_write =3D 0; uart->tx_buffer_status =3D NU_BUFFER_EMPTY; }

.=2Eit goes on - and all works except I loose a full buffer. But since resetting the read and write indices help, it looks like there is a probem with them - since on next round the usart sends characters.

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posted
16 years ago

Mon, Jun 18, 2007 6:15 AM

I received this mail from a user in NL, and have been allowed to post it.It is an important list to keep in mind when we must indeed check all this - if new code does not appear from someone who reckognise our case (to save time for us).

-- User reply -- Case of classical data sharing between interrupt code and task code? Several things you should check:

1) Updates of shared variables in task code should happen with interrupts temporarily disabled. 2) Ideally task only updates read pointer and interrupt should only update write pointer. Decide when to lose characters (buffer==full and new character arrives) 3) Shared variables must be declared with volatile qualifier.