create a segment that overlays memory at a given physical address
#include <sys/seginfo.h> unsigned qnx_segment_overlay( long address, long nbytes );
The qnx_segment_overlay() function allows you to create a segment nbytes long that overlays memory at physical address address. This is often required to address dual-ported memory or system ROM.
The address is a 32-bit long byte address that points to the start of the segment. For example the EGA/VGA graphics memory is located at segment A000, which is byte address 0xA0000. In real mode, there's a restriction that the address must lie on a 16-byte boundary (8086 segmentation).
In the 32-bit version of QNX with paging, the address must start on a 4096 page boundary, and the size must be a multiple of 4096, unless the overlaid memory lies in the range 0xA0000 to 0xFFFFF (system ROM and adapter memory between 640K and 1 meg).
Although this function is available in both the 16-bit and 32-bit libraries, the qnx_segment_... family of calls is primarily intended for the 16-bit segmented version of QNX. To allocate and share memory in the 32-bit version, you should look at using the POSIX shm_open() and mmap() functions. |
A segment number on success. On error, -1 is returned, and errno is set.
#include <stdio.h> #include <i86.h> #include <sys/seginfo.h> void main() { unsigned color_base, mono_base; char __far *cp, __far *mp; /* Create a selector for color video memory */ color_base = qnx_segment_overlay( 0xb8000, 32786 ); /* Create a selector for monochrome video memory */ mono_base = qnx_segment_overlay( 0xb0000, 32786 ); /* Point at byte 100 in the display */ cp = MK_FP( color_base, 100 ); mp = MK_FP( mono_base, 100 ); putchar( '\014' ); fflush( stdout ); /* Set the byte and read it back */ *cp = 'a'; *mp = 'a'; printf( "color_base = %x, cp = %08lx\n", color_base, cp ); printf( "mono_base = %x, mp = %08lx\n", mono_base, mp ); }
QNX
Safety: | |
---|---|
Interrupt handler | No |
Signal handler | Yes, but modifies errno |
Thread | Yes |
errno, qnx_segment_alloc(), qnx_segment_alloc_flags(), qnx_segment_arm(), qnx_segment_flags(), qnx_segment_free(), qnx_segment_get(), qnx_segment_huge(), qnx_segment_index(), qnx_segment_info(), qnx_segment_overlay_flags(), qnx_segment_put(), qnx_segment_raw_alloc(), qnx_segment_raw_free(), qnx_segment_realloc()