gtpm1m4bTPF V4R1 Migration Guide: 3.1 to 4.1

Validating Block Addresses (VALBC)

There are significant changes to the VALBC macro for the TPF 4.1 system. In the TPF 3.1 system, when a block was previously accessed and then released, the VALBC macro returned a condition code of 1 (block not in use). In the TPF 4.1 system, the VALBC macro returns a condition code of either 1 or 2 (block not attached) because in some cases, the control program (CP) returned the frame.