Forum Discussion
Honored ContributorHow to choose device : CPLD or FPGA ?
I want to implement a polynomial function to continuously process a digital temperature signal and output a variable based on such evaluation. What device to look out for ? CPLD or FPGA ?
How can I decide that this implementation would need this much LEs ? Please help in this regard.13 Replies
Altera_ForumWell , I think of going ahead with MAX V CPLD having 570 LEs.
Board cost is also very cheap.- Altera_Forum
Yes, I meant that.
- Altera_Forum--- Quote Start --- I intend to use a fast ( bare ) thermocouple whose response time is 0.3 sec, such that the entire calculation wouldn't cross 0.5 seconds in giving output. --- Quote End --- At speed you also have other options than a CPLD or FPGA ...
- Altera_Forum
I intend to use a fast ( bare ) thermocouple whose response time is 0.3 sec, such that the entire calculation wouldn't cross 0.5 seconds in giving output.
- Altera_Forum--- Quote Start --- Pipe-line the multiplication. You can multiply + accumulate. A MAX II device should do it. --- Quote End --- You mean 'serialise it'. Pipe-lining increases speed but doesn't decrease the amount of LUTs. A 32 by 8 serial multiply takes about 190 Logic Cells in MaxII. This is some 'old' AHDL code I did many years ago, I guess it can be improved upon though. paawansharmas didn't indicate how fast he needs to run.
- Altera_Forum
Pipe-line the multiplication. You can multiply + accumulate. A MAX II device should do it.
- Altera_Forum
It can be done with 38 adders or in total about 1000 'full adders', which comes down to about 1000 LE's for a MAXII device (assuming a few AND-ing functions can be combined at the same time), requiring a EPM1270 device, so you're better off using the smallest of Cyclone II, III or IV series and just use the hardware multipliers.
- Altera_Forum
it wont be as simple as 43 adders
if x is 8 bits, x^2 will need 16 bits, and x^3 needs 24. Then if A,B,C,D are 8 bits again, the output is going to be 32 bits. So thats a lot of adders. Different devices have different size LEs - some have 4input LUTs, some have 6. So to estimate the number of LEs required its simpler just to write the code and compile it. - Altera_Forum
Considering
Y = Ax3 + bx2 + Cx + D I conclude at 5 multipliers and 3 adders ( using both mul. and add.) or 43 addres ( using only adders, for a 8 bit input) It can give a rough estimate of LEs consumed ? - Altera_Forum
Thanks Tricky for your valuable suggestions.
