Mode

0	Copy data to a real memory buffer from an extended memory buffer or vice versa.
1	Access extended memory via a window.

Both spare the user the complexities of protected mode.

Mode 0 allows operation in real mode. smxEMS calls switch into protected mode to perform their functions, then return to real mode. While in protected mode, interrupts are disabled. Typical transfer time for 512 bytes on a 20 MHz 386DX is 375 microseconds.

Mode 1 puts the application and smx into Virtual 8086 mode. In this mode, interrupts are disabled only when changing the window, not when accessing extended memory. Interrupts (which must occur in protected mode) are automatically mapped to the correct real mode interrupt service routines. This adds some overhead to interrupt servicing. The user may choose, instead, to write protected mode isr's.

smxEMS is provided in source code form with on-disk documentation.

smxEMS provides the following services:

Ems_Initialize (mode, size)

Determines amount of extended memory and divides it into blocks. Then establishes VM86 environment, if mode 1 is specified.

Ems_Test ()

Tests if in protected mode

Mode 0:

Ems_Allocate (num_bytes)

Allocates a buffer of size num_bytes. Returns handle to it.

Ems_Free (handle)

Frees buffer.

Ems_CopyTo (handle, real_buf)

Copies from real_buf to extended memory buffer.

Ems_CopyFrom (handle, real_buf)

Inverse.

Mode 1:

Ems_Exit ()

Returns processor to real mode.

Ems_MapPage (seg)

Sets real address of window to seg.

Ems_SetPage (block)

Maps extended memory block to window.