xtos_
Estimates a mapping length from cached channels and rate, then returns a read-only shared mmap address.
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Declaration
#include <xtos/bci.h>
void *xtos_bci_get_mmap_buffer(xtos_bci_session_t *session, size_t *size);Parameters
| Parameter | Type | Description |
|---|---|---|
| session | xtos_bci_session_t * | Non-NULL session handle; the session owns the mapping. |
| size | size_t * | May be NULL; when non-NULL, receives the mapping byte count on success. |
Return value
Returns a borrowed mapping address on success; returns NULL with errno on failure. size is not guaranteed written on failure.
Errors
| errno | Condition |
|---|---|
| EINVAL | session is NULL, or cached information produces a mapping length of zero. |
| ENOMEM/EACCES | mmap cannot establish the mapping or device permission is insufficient. |
| system errno | Preserves errno from mmap failure. |
Notes
- The first call estimates channels×sampling_rate×sizeof(float)×2; later calls return the cached address without recalculation. If GET_INFO failed, cached fields remain zero and the estimated length may be 0, causing mmap to fail; callers must verify cached info before requesting the mapping.
- The public implementation performs several size_t multiplications without explicit overflow checks; callers should validate channel count, sampling rate, and the product range first.
- The mapping uses PROT_READ|MAP_SHARED and is unmapped by destroy; callers must not free or munmap it.
- The public interface provides no write/read position, stable snapshot, or consumer-advance protocol; a pointer alone is not complete zero-copy consumption.
Example
Source
This reference describes headers and implementation at OpenXTOS commit dd313955ad57542bcd2af8827157d1bbd0cf5e83.