h6. [[BufferManager]] h6(. » [[BufferManager SWI Calls|SWI Calls]] h6((. » Buffer_Threshold h2. Buffer_Threshold h5. (SWI &42949) |_<^{width:3em}. Entry | | |<^. R0 |<^. Buffer handle | |<^. R1 |<^. Threshold | |_<^{width:3em}. Exit || |<. R1 |<^. Previous value | h4. Use The threshold value in R1 is -1 to read, and 0 for none. [[OS_UpCall 8]] and [[OS_UpCall 9]] are issued if bit 3 of the [[Buffer Flags Word|buffer_flags]] is set, and the buffer free space crosses the threshold.