<error message>
Error: GXB Central Control Units "gxb0_pathname" and "gxb1_pathname" cannot have the same starting channel number (0)

When implementing multiple transceiver channels on devices with high-speed transceivers, such as Stratix IV GX and Arria II GX, there are multiple ALTGX macros in the design and the starting channel number is not set separately. will result in this error.

This can be resolved by setting the starting channel number differently in each ALTGX macro (starting channel numbers are 0,4,8,12...and multiples of 4).
Example: If you have 4 ALTGX in your design, you can avoid this error by setting them to 0, 4, 8, 12 respectively.

Also, this error is not only for ALTGX but also for various IPs that use high speed transceivers.
Example: If you implement SerialLite II with multiple channels and have multiple SerialLite II macros in your design, you need to set the starting channel number in the settings separately.
Conversely, if you configure multiple channels with one SerialLite II macro, that is, if you have one SerialLite II macro in your design, you do not need to be aware of this start channel number.