When I put the following constraint in the UCF file:
CONFIG PROHIBIT = P32 ;
PAR returns the following error after parsing through the PCF generated from the UCF:
"WARNING:basdp - The SITE "P32" specified in the .PCF file was not found in the design. Please verify that:
1. the specified SITE actually exists in the original design, and
2. the specified SITE record in the .PCF file is spelled correctly.
WARNING:basdp - Ignoring constraint "PROHIBIT = SITE "P32"; " because site not found
ERROR:baspw - The .pcf file contains errors/warnings. PAR cannot proceed."
In the error message, P32 is actually the MD0 (mode pin) for a PC84 package. This is not a standard I/O. The Boundary Scan and Mode pins TDI, TCK, TMS, TDO, MD0, MD1, and MD2 are considered special purpose pins, and they will be used only if the TCK, TDI, TMS, TDO, MD0, MD1, and MD2 pads are specifically placed (instantiated) in the design. The others mentioned (HDC, LDC, INIT, DIN, DOUT) do need to be prohibited and will be used indiscriminately by the software.
M1 issues an "unknown site" error message if a PROHIBIT constraint is placed on a Boundary Scan or Mode pin site. Essentially, you can be assured that the M1 (Alliance) software will only use the Boundary Scan or Mode pins for I/O when the components are specifically placed (instantiated) in the design; there is no reason to prohibit those sites.
PROGRAM, CCLK, and DONE cannot be prohibited, as they are not I/Os.
The "P" for P26 (or any other regular I/O) must be capitalized.