Reply by Purushottam Mishra _98d07036_●June 24, 20022002-06-24
Hi all,
I am using DSK6211 kit with codec TLC320AD535.
I am facing a problem here.
When I feed a digital signal (such as negative square wave 0 to -1) to
the DAC ( by McBSP_write() function) the analog waveform as seen at the
output of the DAC in an oscillator comes to be exactly opposite to what
is expected ( a square wave of 0V to 1V). But, when a feed a positive signal
of ( 0V - 1V) the waveform obtained at the output is ( -0.5V to 0.5V).
The signal gets shifted equally around the x-axis.
Please help.
Purushottam.
Reply by Brad Cadle●June 24, 20022002-06-24
I have not looked at the SPRA document in a while, but we had some severe
problems with the first iteration of the document. Indeed the revision of
the document we used last year (SPRA633 without the A) had typo's in the
example code!! We ended having better success writing our own driver from
scratch.
Here are a couple of issues and mistakes we made which caused problems in
our attempts using our own code:
1) We initially used some bitwise & and | operators on the some write
only
EDMA registers which really messed things up.
2) We had a lot of difficulty having our EDMA bit buffers off chip. The
problem was EDMA would write directly to offchip memory and if you did not
tell the processor to resolve the cache mis-match we we would generally find
the first bit or two wrong. The easy fix is to configure the processor to
1/4 sram and 3/4 Cache and then EDMA the bits into on-chip memory (or do not
use cache at all which would be a waste). A more difficult fix is to tell
the processor to resolve the cache mis-match in the EDMA ISR, wait for the
mis-match to resolve and then convert the bits into bytes.
Once we moved beyond these two major issues our own driver seemed to work
well. Incidently we used the on-chip clock to drive the mcbsp and had to
use 32 bit wide words for bit frames rather than 16 bit to cover the baud
rates we needed.
-----Original Message-----
From: [mailto:]
Sent: Monday, June 24, 2002 9:23 AM
To:
Subject: [c6x] McBSP & UART
Hi,
We are trying to use the McBSP to interface to a UART. we followed the
application report document (SPRA633A) for TI. For a loop back mode it works
fine, we get what ever we sent. Connecting to a serial PC port it seems we
are missing the first 2 bits and the data is completely out of Synch. Any
idea what could be the cause? Thanks.
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About this discussion group:
Hi,
We are trying to use the McBSP to interface to a UART. we followed the
application report document (SPRA633A) for TI. For a loop back mode it works
fine, we get what ever we sent. Connecting to a serial PC port it seems we
are
missing the first 2 bits and the data is completely out of Synch.
Any idea what could be the cause?
Thanks.