1) In MAX 10 series , there are embedded 18x18 multipliers, each 18x18 multiplier can be used as two 9x9 multipliers(mentioned in the document page-3)
2) But in Cyclone V devices , its mentioned that each DSP can give three 9x9 multipliers or two 18x18 multipliers. (page 20 in doc - https://www.intel.com/content/dam/www/programmable/us/en/pdfs/literature/hb/cyclone-v/cv_51001.pdf )
If that is the case , I understand each 18x18 multiplier cannot give us two 9x9 in cyclone V devices . Why it is so?
Since each DSP have two 18x18 multipliers, Can I somehow split each 18x18 multipliers into two independent 9x9 multipliers? So
that each DSP provide me four 9x9 multipliers?
Yes, your understanding is correct. A CV DSP block can only implement max three 9x9 multipliers. You may refer to the CV device handook vol 1 -> "CV Variable Precision DSP Blocks Operational Modes for Cyclone V Devices" for supported operational modes. There is no specific explanation on why max three 9x9 multipliers but I believe it is limited by the internal architecture of the DSP block.