RM0440 Rev 4 477/2126
RM0440 CORDIC co-processor (CORDIC)
485
Figure 40. CORDIC convergence for square root
Note: The convergence rate decreases as the quantization error starts to become significant.
The CORDIC can perform four iterations per clock cycle. For each function, the maximum
error remaining after every four iterations is shown in Table 115, together with the number of
clock cycles required to reach that precision. From this table, the desired number of cycles
can be determined and programmed in the PRECISION field of the CORDIC_CR register.
The co-processor stops as soon as the programmed number of iterations has completed,
and the result can be read immediately.
Table 115. Precision vs. number of iterations
Function
Number of
iterations
Number of
cycles
Max residual error
(1)
q1.31 format q1.15 format
Sin, Cos,
Phase
(2)
, Mod,
Atan
(4)
412
-3
2
-3
822
-7
2
-7
12 3 2
-11
2
-11
16 4 2
-15
2
-15
20 5 2
-18
2
-16
24 6 2
-19
2
-16
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