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VSTa manual pages  - ENABLE_DMA (2)

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enable_dma - enable DMA abilities for current process

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Synopsis
Description
Notes

#include <sys/syscall.h>
int enable_dma(int channel);

The enable_dma() system call changes the behavior of the kernel to permit a server to operate in a DMA mode. In particular, the process is permitted to use the page_wire() and page_release() system calls, and messages received using msg_receive() are mapped into a DMA server’s address space as writable pages, thus permitting programmed I/O directly into a client’s memory.

This call is generally useful only to DMA-based I/O servers, although certain transaction-oriented direct I/O filesystems might benefit.

The argument is the DMA channel to be used by a hardware DMA server. On architectures where there is no concept of DMA channels, it may be passed as 0. On the x86, this argument is currently unused.