Why does reconfiguration of the Hard Processor System (HPS) over JTAG fail for Intel® Agilex™ and Intel® Stratix® 10 devices after a corrupted bitstream has been loaded through U-boot?

Due to a known problem in Intel® Quartus® Prime Pro Edition software version 20.3, loading a corrupted bitstream through U-boot on Intel® Agilex™ and Intel® Stratix® 10 devices will create an error state that prevents reconfiguration of the Hard Processing Ssystem (HPS) over JTAG.  You may see the following error messages when attempting to reconfigure the HPS over JTAG with a good bitstream.

Error (18939):  Unexpected error in JTAG server:  JTAG chain broken

Error (18947):  Device not responding

If a corrupted HPS bitstream is loaded through U-boot, you can work around this problem by power cycling the device.  This will allow you to successfully reconfigure the HPS over JTAG with a good bitstream.

This problem is fixed starting with the Intel® Quartus® Prime Pro Edition software version 20.4.