Struct Request

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pub struct Request { /* private fields */ }

Expand description

A run of sectors to read into memory.

Built with Request::new_raw, then refined with the with_* methods.

Implementations§

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impl Request

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pub const unsafe fn new_raw( lba: u32, sectors: u32, destination: *mut u32, ) -> Self

Read sectors sectors starting at lba (program-relative, shifted by the loader’s disc base like every SDK disc read) into destination.

§Safety

destination must be word-aligned and valid for writes of sectors * 2048 bytes, and nothing else may read or write that memory from the moment the request is submitted until it has finished (see Engine::state). The transport writes from the interrupt handler, so the memory is not held by any borrow the compiler can see. Memory that is only ever read through read_volatile until the request finishes meets this.

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pub const fn with_priority(self, priority: Priority) -> Self

Serve this request at priority.

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pub const fn with_resumes(self, times: u8) -> Self

Let the transport pick this request up again from where it stopped, up to times times, when the drive reports an error mid-transfer. Each resume costs the recovery pause and one seek. With 0 (the default) an error ends the request as Outcome::Failed and the caller decides.

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pub const fn with_byte_len(self, bytes: u32) -> Self

Store only bytes bytes instead of sectors * 2048: the last sector is popped whole but only its first words, rounded up to a word, are written, so a transfer never writes past a chunk that does not end on a sector boundary.

bytes must lie in (sectors - 1) * 2048 + 1 ..= sectors * 2048; anything else is ignored (every sector stored whole). The destination then only has to be valid for bytes rounded up to a word.

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pub const fn lba(&self) -> u32

First sector.

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pub const fn sectors(&self) -> u32

Sector count.

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pub const fn priority(&self) -> Priority

Priority.

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pub const fn end_lba(&self) -> u32

The sector after the last one, where a request that can chain onto this one starts.

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pub unsafe fn remaining_after(&self, received: u32) -> Option<Request>

The rest of this request after received sectors landed: the request to submit to continue an aborted or failed transfer. None when nothing is left.

The result is a request like any other. It starts with a fresh seek, at lba + received, into the destination advanced by received sectors, with the same priority and resume budget.

§Safety

received must be a count the transport reported for this request (or lower): the memory the new request writes is the tail of this request’s destination, and the safety contract of new_raw applies to it again.