TigerSHARC CLU Closer look at the XCORRS M. Smith, University of Calgary, Canada [email protected] The practice
Suppose we have the vector in-phase and out-of- phase data gathered over an antenna from a satellite for example. Gain issues make it x16 -16-16j, 16+16j, 16+16j, -16-16j 16+16j, 16+16j -16-16j, 16+16j, 16+16j, -16-16j 16+16j, 16+16j, -16-16j
16+16j, 16+16j, etc Question if the original data from the satellite had this form -1-j,1+j,1+j, -1-j,1+j,1+j, -1-j,1+j,1+j, -1-j,1+j,1+j, -1-j,1+j,1+j, -1-j,1+j,1+j, How is the satellite data delayed? FOR THIS EXAMPLE .. 0, 3, 6, 9, 12 etc
Tackle the issue with FIR First modify correlation function to handle complex values
Ignore that issue at the moment Imagine 1024 data points + 1024 PRN Need to do 1024 FIR each of 1024 taps We know how to optimize to do 2 taps every cycle (one in X and one in Y) Cycle time is 1024 * 512 cycles = 1 ms at 500 MHz
XCORS can do 8 * 16 taps each cycle in each compute block 148 times faster Where does the CLU fit in? XCORRS definition
Uses registers TR D C And something called CUT
THEORY Mathematical definition Satellite data
Quad fetch brings in 8 complex values 8 bits each Pattern here is -1 + 0j, 1 + 0j, 1 + 0j, -1 + 0j, 1 + 0j, 1 + 0j, . PRN code 2 bit complex number Seems strange to have two dummy bits
But actually makes sense PRN -1+ -1j, 1 + j, 1 + j, -1 + -1j, 1 + j, 1 + j, . +1, -1 are associated with the PSK more next lecture Problem BINARY means 1 and 0, so how represent 1 and -1 PRN
PRN 0x3 value go in as C15 and C16 0011 -- C15 = -1 j C16 = +1 + j
Loading the THR registers Standard XCORRS instruction Lower 46 bits ofTHR1:0 R7:3
TR15 += D7 * C7 + D6 * C6 + 8 taps 64 taps each cycles on both x and y compute blocks if set up properly 128 taps each cycle these are complex taps compared to 2 real taps / cycle after lab. 3 TR15:0 = XCORRS(R7:4, THR3:0) (CUT -7)
Final Result Maximum correlation occurs every 3 shifts which is what we expect Is it the correct results Correlation result expected In step
-1 +0j, 1 + 0j, 1 + 0j, 16 times with -1 - j, 1 + j, 1 + j, 16 times -1 * -1 + 1 * 1 + 1 * 1 + 48 = 0x30 -- Real component
Out of step -1 +0j, 1 + 0j, 1 + 0j, 16 times with 1 + j, 1 + j, -1 - j, 16 times -1 * 1 + 1 * 1 + 1 * -1 + -16 = -0x10 = 0xFFF0
Final Result 1) Now have correlation values for 16 shifts in TR registers store to external memory Repeat for all other necessary shifts find the maximum 2) Now make parallel in SISD mode 3) Now make parallel in SIMD
Take home Quiz 4 Old requirement Do Lab 4 with FFT and XCORRS Write tests and demonstrate XCORRS used for correlation a) Not parallel instruction format but in a loop b) Now do in optimized SISD mode c) Now do in optimized SIMD mode
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