int isa_dma_acquire(int chanel_number)

Reserve a DMA channel. Returns 0 on success or EBUSY if the channel was already reserved by this or a different driver. Most of the ISA devices are not able to share DMA channels anyway, so normally this function is called when attaching a device. This reservation was made redundant by the modern interface of bus resources but still must be used in addition to the latter. If not used then later, other DMA routines will panic.

int isa_dma_release(int chanel_number)

Release a previously reserved DMA channel. No transfers must be in progress when the channel is released (in addition the device must not try to initiate transfer after the channel is released).

void isa_dmainit(int chan, u_int bouncebufsize)

Allocate a bounce buffer for use with the specified channel. The requested size of the buffer can not exceed 64KB. This bounce buffer will be automatically used later if a transfer buffer happens to be not physically contiguous or outside of the memory accessible by the ISA bus or crossing the 64KB boundary. If the transfers will be always done from buffers which conform to these conditions (such as those allocated by bus_dmamem_alloc() with proper limitations) then isa_dmainit() does not have to be called. But it is quite convenient to transfer arbitrary data using the DMA controller. The bounce buffer will automatically care of the scatter-gather issues.

void isa_dmastart(int flags, caddr_t addr, u_int nbytes, int chan)

Prepare to start a DMA transfer. This function must be called to set up the DMA controller before actually starting transfer on the device. It checks that the buffer is contiguous and falls into the ISA memory range, if not then the bounce buffer is automatically used. If bounce buffer is required but not set up by isa_dmainit() or too small for the requested transfer size then the system will panic. In case of a write request with bounce buffer the data will be automatically copied to the bounce buffer.

flags - a bitmask determining the type of operation to be done. The direction bits B_READ and B_WRITE are mutually exclusive.

addr - virtual address of the buffer

nbytes - length of the buffer. Must be less or equal to 64KB. Length of 0 is not allowed: the DMA controller will understand it as 64KB while the kernel code will understand it as 0 and that would cause unpredictable effects. For channels number 4 and higher the length must be even because these channels transfer 2 bytes at a time. In case of an odd length the last byte will not be transferred.

chan - channel number

void isa_dmadone(int flags, caddr_t addr, int nbytes, int chan)

Synchronize the memory after device reports that transfer is done. If that was a read operation with a bounce buffer then the data will be copied from the bounce buffer to the original buffer. Arguments are the same as for isa_dmastart(). Flag B_RAW is permitted but it does not affect isa_dmadone() in any way.

int isa_dmastatus(int channel_number)

Returns the number of bytes left in the current transfer to be transferred. In case the flag B_READ was set in isa_dmastart() the number returned will never be equal to zero. At the end of transfer it will be automatically reset back to the length of buffer. The normal use is to check the number of bytes left after the device signals that the transfer is completed. If the number of bytes is not 0 then something probably went wrong with that transfer.

int isa_dmastop(int channel_number)

Aborts the current transfer and returns the number of bytes left untransferred.