=> R1 = &78 (reason code)
<= preserve all regisers to pass on, else
R1 = 0 (claimed)
R3 = pointer to 20 byte block
This service is issued when a PDriver module is about to open Resources:$.Resources.PDrivers.Messages. If another PDriver module has already opened this file, it should claim the service and return the block.
If a PDriver module issues this service and it goes unclaimed, it should allocate 20 bytes with OS_Module 6, pass the block to MessageTrans_OpenFile, and set the last word (usage count) to 1.
If the service is claimed, then the PDriver module should increase the usage count in the block by 1.
Either way, when the PDriver module is finished with the file, it should decrease the usuage count in the block by 1. If this reduces the count to 0, it should call MessageTrans_CloseFile and then OS_Module 7 to free the block.
Simple eh?
See PRM 3, page 600
PDriverGetMessages Block
Size Meaning
16 MessageTrans block, from MessageTrans_OpenFile
4 usage count
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