When testing the Post Configuration CRC feature, I find that INIT is not behaving as expected when I download via JTAG.
Should I be using this feature when configuring via JTAG?
The Post Configuration CRC feature provides an external flag to the system using the INIT pin.
For SPI, BPI, Serial, and SelectMAP modes, the INIT pin will flag CRC errors when the device is loaded via the Flash or via JTAG.
In ISF mode for the Spartan-3AN device, the internal flash will be required to load the FPGA before the CRC feature can be tested. The INIT pin will not properly flag an error if JTAG is used.
When the mode pins set to JTAG, the INIT pin does not reflect the status of the CRC register and will not provide a valid flag as to the state of the CRC checking. Therefore, this feature will not be available when the device is in JTAG mode as there is no other way to check the status of the CRC checker.
iMPACT will also read the Status Register for the Spartan-3A/AN devices. The status register contains the "POST_CRC_ERR error" bit. This bit will not accurately reflect the status of the Post Config CRC error and will always read a "0". This will be removed from the software, but for the time being, please ignore this bit reading.