DMA

86Box offers two mechanisms for Direct Memory Access: 8237 DMA for ISA devices and direct memory read/write for PCI devices.

8237 DMA

86box/dma.h provides the dma_channel_read and dma_channel_write functions to read or write (respectively) a value from or to an 8237 DMA channel.

dma_channel_read

Parameter	Description
channel	DMA channel number: 0-3 for 8-bit channels or 5-7 for 16-bit channels.
Return value	8- (channels 0-3) or 16-bit (channels 5-7) value read from the given DMA channel, or DMA_NODATA if no data was read. May include a DMA_OVER bit flag (located above the most significant data bit so as to not interfere with the data) indicating that this was the last byte or word transferred, after which the channel is auto-initialized or masked depending on its configuration.

dma_channel_write

Parameter	Description
channel	DMA channel number: 0-3 for 8-bit channels or 5-7 for 16-bit channels.
val	8- (channels 0-3) or 16-bit (channels 5-7) value to write to the given DMA channel.
Return value	0 on success; DMA_NODATA if no data was actually written; DMA_OVER if this was the last byte or word transferred, after which the channel is auto-initialized or masked depending on its configuration.

Direct memory read/write

86box/mem.h provides the mem_read*_phys and mem_write*_phys functions, which read or write physical memory directly. These are useful for PCI devices, which perform DMA on their own.

mem_readb_phys / mem_readw_phys / mem_readl_phys

Parameter	Description
addr	32-bit memory address to read.
Return value	8- (mem_readb_phys), 16- (mem_readw_phys) or 32-bit (mem_readl_phys) value read from the given memory address.

mem_writeb_phys / mem_writew_phys / mem_writel_phys

Parameter	Description
addr	32-bit memory address to write.
val	8- (mem_readb_phys), 16- (mem_readw_phys) or 32-bit (mem_readl_phys) value to write to the given memory address.