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Serial port stream operations
OS_Pb, write byte to serial port device (IX handle)
OS_Pbt, write byte to serial port device (IX handle), with timeout
OS_Gb, get byte from serial port device (IX handle)
OS_Gbt, get byte from serial port device (IX handle) with timeout
OS_Si, low level serial port interface
Filenames
GN_Esa, read & write to filename segments
GN_Fcm, produce compressed filename
GN_Fex, expand a filename
GN_Opw, open wildcard handler
GN_Pfs, parse filename segment
GN_Prs, parse filename
GN_Wcl, close wildcard handle
GN_Wfn, fetch next match for wildcard string (handle)
GN_Wsm, match filename segment to wildcard string
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