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When I transmit over spi it also seems to be receiving (when i don't want it to). Should I transmit whatever I need to. _Then_ enable the receive part of the mcbsp, then send a "dummy" transmit to get the clocks, then read DRR, then disable receive, and transmit again...? will this give me the correct data? as of now, i am getting the wrong data despite the fact that the data is being correctly output on DR by the ext SPI device (verified on a scope). |
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mcbsp spi receive
Started by ●October 8, 2002
Reply by ●October 8, 20022002-10-08
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Lucy, Customarily, when you clock data out on an SPI channel, data is simultaneously clocked in to your receive register. You have to determine whether this data is useful, or should be ignored. It sounds like in your case, the data should be ignored. Then, when you want to receive data, you need to transmit dummy data, then immediately do a couple of reads of the SPI receive register to flush it out of any buffered data, and then wait for the real receive dat to come in. Ususlly this is done with interrupts to avoid wasted CPU cycles in a wait loop. All of the above assumes that you are programming the *master* SPI device. Hope this helps, Best Regards, Tony ______________________________ Tony Zampini () Director of Engineering DSP Global Inc. 33 Plan Way, Bldg. #4 Warwick, RI 02886 Tel. 401-737-9900 FAX: 401-739-4197 www.dspglobal.com ----- Original Message ----- From: "Lucy Jordan" <> To: <> Sent: Monday, October 07, 2002 10:34 PM Subject: [c54x] mcbsp spi receive > When I transmit over spi it also seems to be receiving (when i don't > want it to). > Should I transmit whatever I need to. _Then_ enable the receive part > of the mcbsp, then send a "dummy" transmit to get the clocks, then > read DRR, then disable receive, and transmit again...? will this give > me the correct data? as of now, i am getting the wrong data despite > the fact that the data is being correctly output on DR by the ext SPI > device (verified on a scope). > _____________________________________ > Note: If you do a simple "reply" with your email client, only the author of this message will receive your answer. You need to do a "reply all" if you want your answer to be distributed to the entire group. > > _____________________________________ > About this discussion group: > > To Join: Send an email to > > To Post: Send an email to > > To Leave: Send an email to > > Archives: http://www.yahoogroups.com/group/c54x > > Other Groups: http://www.dsprelated.com > ">http://docs.yahoo.com/info/terms/ > |
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Reply by ●October 8, 20022002-10-08
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Yes don't enable the receive until you expect data back from the SPI your clocking out to. Also be sure to clear the DR beforehand its tripple buffered and may contain old data. Phil --- In c54x@y..., "Lucy Jordan" <screaminglucy@y...> wrote: > When I transmit over spi it also seems to be receiving (when i don't > want it to). > Should I transmit whatever I need to. _Then_ enable the receive part > of the mcbsp, then send a "dummy" transmit to get the clocks, then > read DRR, then disable receive, and transmit again...? will this give > me the correct data? as of now, i am getting the wrong data despite > the fact that the data is being correctly output on DR by the ext SPI > device (verified on a scope). |
Reply by ●October 8, 20022002-10-08
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I'm not concerned with wasting cycles while I poll, so do you think the following would work? The dsp is the spi master. void spi_send () { check xrdy write data to DXR wait for rrdy //wait for output data to be shifted out read DRR //clear rrdy for garbage data } unsigned char spi_receive() { check xrdy write dummy data to DXR wait for rrdy //wait for receive to complete read DRR //this should be correct data? } -----Original Message----- From: Tony Zampini Sent: Tuesday, October 08, 2002 9:02 AM To: ; Lucy Jordan Subject: Re: [c54x] mcbsp spi receive Lucy, Customarily, when you clock data out on an SPI channel, data is simultaneously clocked in to your receive register. You have to determine whether this data is useful, or should be ignored. It sounds like in your case, the data should be ignored. Then, when you want to receive data, you need to transmit dummy data, then immediately do a couple of reads of the SPI receive register to flush it out of any buffered data, and then wait for the real receive dat to come in. Ususlly this is done with interrupts to avoid wasted CPU cycles in a wait loop. All of the above assumes that you are programming the *master* SPI device. Hope this helps, Best Regards, Tony ______________________________ Tony Zampini () Director of Engineering DSP Global Inc. 33 Plan Way, Bldg. #4 Warwick, RI 02886 Tel. 401-737-9900 FAX: 401-739-4197 www.dspglobal.com ----- Original Message ----- From: "Lucy Jordan" <> To: <> Sent: Monday, October 07, 2002 10:34 PM Subject: [c54x] mcbsp spi receive > When I transmit over spi it also seems to be receiving (when i don't > want it to). > Should I transmit whatever I need to. _Then_ enable the receive part > of the mcbsp, then send a "dummy" transmit to get the clocks, then > read DRR, then disable receive, and transmit again...? will this give > me the correct data? as of now, i am getting the wrong data despite > the fact that the data is being correctly output on DR by the ext SPI > device (verified on a scope). > _____________________________________ > Note: If you do a simple "reply" with your email client, only the author of this message will receive your answer. You need to do a "reply all" if you want your answer to be distributed to the entire group. > > _____________________________________ > About this discussion group: > > To Join: Send an email to > > To Post: Send an email to > > To Leave: Send an email to > > Archives: http://www.yahoogroups.com/group/c54x > > Other Groups: http://www.dsprelated.com > ">http://docs.yahoo.com/info/terms/ |
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Reply by ●October 8, 20022002-10-08
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Yes, I would just add one thing to your spi_send() function to insure that no old receive data is sitting in the receive fifo: void spi_send () { check xrdy write data to DXR -> read DRR -> read DRR wait for rrdy //wait for output data to be shifted out read DRR //clear rrdy for garbage data } Tony ----- Original Message ----- From: "Lucy Jordan" <> To: "'Tony Zampini'" <> Cc: <> Sent: Tuesday, October 08, 2002 3:48 PM Subject: RE: [c54x] mcbsp spi receive > > I'm not concerned with wasting cycles while I poll, so do you think the > following would work? > The dsp is the spi master. > > void spi_send () > { > check xrdy > write data to DXR > wait for rrdy //wait for output data to be shifted out > read DRR //clear rrdy for garbage data > } > unsigned char spi_receive() > { > check xrdy > write dummy data to DXR > wait for rrdy //wait for receive to complete > read DRR //this should be correct data? > } > > -----Original Message----- > From: Tony Zampini > Sent: Tuesday, October 08, 2002 9:02 AM > To: ; Lucy Jordan > Subject: Re: [c54x] mcbsp spi receive > > Lucy, > Customarily, when you clock data out on an SPI channel, data is > simultaneously > clocked in to your receive register. You have to determine whether this > data > is > useful, or should be ignored. It sounds like in your case, the data > should > be ignored. Then, when you want to receive data, you need to transmit > dummy > data, then immediately do a couple of reads of the SPI receive register > to > flush it > out of any buffered data, and then wait for the real receive dat to come > in. > Ususlly this is done with interrupts to avoid wasted CPU cycles in a > wait > loop. > > All of the above assumes that you are programming the *master* SPI > device. > > Hope this helps, > > Best Regards, > Tony > ______________________________ > Tony Zampini () > Director of Engineering > DSP Global Inc. > 33 Plan Way, Bldg. #4 > Warwick, RI 02886 > Tel. 401-737-9900 > FAX: 401-739-4197 > www.dspglobal.com > > ----- Original Message ----- > From: "Lucy Jordan" <> > To: <> > Sent: Monday, October 07, 2002 10:34 PM > Subject: [c54x] mcbsp spi receive > > When I transmit over spi it also seems to be receiving (when i don't > > want it to). > > Should I transmit whatever I need to. _Then_ enable the receive part > > of the mcbsp, then send a "dummy" transmit to get the clocks, then > > read DRR, then disable receive, and transmit again...? will this give > > me the correct data? as of now, i am getting the wrong data despite > > the fact that the data is being correctly output on DR by the ext SPI > > device (verified on a scope). > > > > > > > > > > > > _____________________________________ > > Note: If you do a simple "reply" with your email client, only the > author > of this message will receive your answer. You need to do a "reply all" > if > you want your answer to be distributed to the entire group. > > > > _____________________________________ > > About this discussion group: > > > > To Join: Send an email to > > > > To Post: Send an email to > > > > To Leave: Send an email to > > > > Archives: http://www.yahoogroups.com/group/c54x > > > > Other Groups: http://www.dsprelated.com > > > > > > ">http://docs.yahoo.com/info/terms/ > > > > > |
Reply by ●October 9, 20022002-10-09
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Hi Lucy Looks like that will work. The only thing I do differnet is disable the recieve via the RRST in the SPCR1 until I expect data in. Phil --- In c54x@y..., "Lucy Jordan" <screaminglucy@y...> wrote: > > I'm not concerned with wasting cycles while I poll, so do you think the > following would work? > The dsp is the spi master. > > void spi_send () > { > check xrdy > write data to DXR > wait for rrdy //wait for output data to be shifted out > read DRR //clear rrdy for garbage data > } > unsigned char spi_receive() > { > check xrdy > write dummy data to DXR > wait for rrdy //wait for receive to complete > read DRR //this should be correct data? > } > > -----Original Message----- > From: Tony Zampini > Sent: Tuesday, October 08, 2002 9:02 AM > To: c54x@y...; Lucy Jordan > Subject: Re: [c54x] mcbsp spi receive > > Lucy, > Customarily, when you clock data out on an SPI channel, data is > simultaneously > clocked in to your receive register. You have to determine whether this > data > is > useful, or should be ignored. It sounds like in your case, the data > should > be ignored. Then, when you want to receive data, you need to transmit > dummy > data, then immediately do a couple of reads of the SPI receive register > to > flush it > out of any buffered data, and then wait for the real receive dat to come > in. > Ususlly this is done with interrupts to avoid wasted CPU cycles in a > wait > loop. > > All of the above assumes that you are programming the *master* SPI > device. > > Hope this helps, > > Best Regards, > Tony > ______________________________ > Tony Zampini (tony@d...) > Director of Engineering > DSP Global Inc. > 33 Plan Way, Bldg. #4 > Warwick, RI 02886 > Tel. 401-737-9900 > FAX: 401-739-4197 > www.dspglobal.com > > ----- Original Message ----- > From: "Lucy Jordan" <screaminglucy@y...> > To: <c54x@y...> > Sent: Monday, October 07, 2002 10:34 PM > Subject: [c54x] mcbsp spi receive > > When I transmit over spi it also seems to be receiving (when i don't > > want it to). > > Should I transmit whatever I need to. _Then_ enable the receive part > > of the mcbsp, then send a "dummy" transmit to get the clocks, then > > read DRR, then disable receive, and transmit again...? will this give > > me the correct data? as of now, i am getting the wrong data despite > > the fact that the data is being correctly output on DR by the ext SPI > > device (verified on a scope). > > > > > > > > > > > > _____________________________________ > > Note: If you do a simple "reply" with your email client, only the > author > of this message will receive your answer. You need to do a "reply all" > if > you want your answer to be distributed to the entire group. > > > > _____________________________________ > > About this discussion group: > > > > To Join: Send an email to c54x-subscribe@y... > > > > To Post: Send an email to c54x@y... > > > > To Leave: Send an email to c54x-unsubscribe@y... > > > > Archives: http://www.yahoogroups.com/group/c54x > > > > Other Groups: http://www.dsprelated.com > > > > > > ">http://docs.yahoo.com/info/terms/ > > > > > > |
