A JAM/STAPL file or SVF file contains all vectors necessary to communicate with whatever is connected to the JTAG chain. It should not be necessary to run the DETECT command before running STAPL or SVF. It should be OK to run these commands with null parts.
This issue arrises when programming through a JTAG scan-bridge device (e.g. Firecron JTX chips). This type of device does not become selected until the appropriate address is sent with Shift-IR. This select vector must be added to the STAPL code (along with additional configuration instructions) before programming vectors can pass through the bridge to secondary JTAG chains.
The bottom line here is that a Firecron scan bridge will not respond to the DETECT command and thus a NULL parts should be valid for stapl programming (and presumably SVF programming as well.)
Fixing this in stapl.c was a simple matter of removing the check for null chain->parts.
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