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Hi all, I'm new to the C6711DSK and have a question regarding DSP/BIOS data types. I'm outputting a 100Hz sin wave from my 88.2kHz DAC. To produce this signal, I've filled a buffer of size 882, as follows - Float sig[100]; Void main() { Int i; for(i=0;i<882;i++) sig[i] = cos(2*PI*100*i/(Float)(SR)); McBSP_Init(); EDMA_Init(); return; } With this code I get a load of about 70%, but when I change my declaration to - float sig[882]; and change nothing else, the load drops to 15% or so. Why is this? I've also noticed that if I set the frequency of the output signal to 400Hz, with the same buffer size, my output has a slight distortion. This glitch appears as if one of the samples is being outputted incorrectly for every cycle of the signal. Its as if, a value is being writen to the sig buffer which shouldn't be there. This glitch occurs if I declare sig as - float sig[100]; but disappears if I use - Float sig[100]; If I declare the following - float sig1[100]; //not used float sig[100]; the glitch again disappears. When should I use DSP/BIOS data types and when should I not? I plan to write a PC application which allows the user to specify the frequency they wish to output. To do this I was going to create a memory segment of size 882, at base 0x20. I have the DSP set for 3 way cache. The PC would then write in the samples to this buffer for outputting. The available frequencies would be multiples of 100Hz. Is this the best approach? Thanks, Fran. |
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DSP/BIOS Float[] Vs float[]
Started by ●January 26, 2004
Reply by ●January 27, 20042004-01-27
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Rockall- There is a lot work in your e-mail explanation so maybe I'm missing something by asking this, but why would u ever declare the size of sig[] to be less than 882, if your loop length is always 882? -Jeff > I'm new to the C6711DSK and have a question regarding DSP/BIOS data > types. I'm outputting a 100Hz sin wave from my 88.2kHz DAC. To > produce this signal, I've filled a buffer of size 882, as follows - > > Float sig[100]; > > Void main() > { > Int i; > > for(i=0;i<882;i++) > sig[i] = cos(2*PI*100*i/(Float)(SR)); > > McBSP_Init(); > EDMA_Init(); > > return; > } > > With this code I get a load of about 70%, but when I change my > declaration to - > > float sig[882]; > > and change nothing else, the load drops to 15% or so. Why is this? > > I've also noticed that if I set the frequency of the output signal to > 400Hz, with the same buffer size, my output has a slight distortion. > This glitch appears as if one of the samples is being outputted > incorrectly for every cycle of the signal. Its as if, a value is > being writen to the sig buffer which shouldn't be there. This glitch > occurs if I declare sig as - > > float sig[100]; > > but disappears if I use - > > Float sig[100]; > > If I declare the following - > > float sig1[100]; //not used > float sig[100]; > > the glitch again disappears. When should I use DSP/BIOS data types > and when should I not? > > I plan to write a PC application which allows the user to specify the > frequency they wish to output. To do this I was going to create a > memory segment of size 882, at base 0x20. I have the DSP set for 3 > way cache. The PC would then write in the samples to this buffer for > outputting. The available frequencies would be multiples of 100Hz. Is > this the best approach? > > Thanks, > > Fran. > > _____________________________________ > 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/c6x > > Other Groups: http://www.dsprelated.com > |
