The high-level code supplies a pair of memory allocation functions,
150 and 151, which are guaranteed to return
memory in the first 16~MB of physical memory. This memory is, therefore,
suitable for use with DMA. The amount of memory allocated per request <#1428#>
must<#1428#> be a multiple of 512 bytes, and <#1429#> must<#1429#> be less than or
equal to 4096 bytes. The total amount of memory available via
152 is a complex function of the 153
structure variables 154, 155, and
156.
The 157 pointer is available to point to a region of
memory allocated with 158. The low-level SCSI driver is
responsible for managing this pointer and its associated memory, and should
free the area when it is no longer needed.