Twim: Implicitly copy buffer into RAM if needed when using embedded hal traits #165
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…mbedded hal trait
… using embedded hal traits
…already be in RAM, so no check neccessary
kalkyl
changed the title
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Could you be so kind and run |
| unsafe { w.maxcnt().bits(rx_buffer.len() as _) }); | ||
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| // Chunk write data | ||
| let wr_buffer = &mut [0; FORCE_COPY_BUFFER_SIZE][..]; |
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| let wr_buffer = &mut [0; FORCE_COPY_BUFFER_SIZE][..]; | |
| let wr_buffer = &mut [0; FORCE_COPY_BUFFER_SIZE.min(EASY_DMA_SIZE)][..]; |
I think we should take the minimum here too? Or ensure elseplace that FORCE_COPY_BUFFER_SIZE is always <= EASY_DMA_SIZE. Maybe we should do that where we define FORCE_COPY_BUFFER_SIZE even?
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Yes, i don't know how to do that min check in const though?
I guess ensuring FORCE_COPY_BUFFER_SIZE <= EASY_DMA_SIZE where we define FORCE_COPY_BUFFER_SIZE is the best solution, then we can just use FORCE_COPY_BUFFER_SIZE for our buffer and chunk sizes?
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Ok, I think we should use .min() at both places or at no place in this code then :) Otherwise it's just confusing I think.
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Totally agree, so i will use FORCE_COPY_BUFFER_SIZE in both places then :)
How can i assert FORCE_COPY_BUFFER_SIZE <= EASY_DMA_SIZE when they are defined in "top-level"?
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I am not sure we can ensure this at compile time other than manually making sure of this and maybe add a comment.
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The only hacky way i can think of right now is not pretty and not zero cost, something like:
const _CHECK_FORCE_COPY_BUFFER_SIZE: usize = EASY_DMA_SIZE - FORCE_COPY_BUFFER_SIZE;
// ERROR: FORCE_COPY_BUFFER_SIZE must be <= EASY_DMA_SIZE
..that would fail with "attempt to subtract with overflow" :)
But i guess just a comment should be enough right?
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Wont it just optimize that out and thus be zero cost?
| self.0.events_lastrx.write(|w| w); // reset event | ||
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| // Stop read operation | ||
| self.0.tasks_stop.write(|w| |
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Doesn't it stop automatically when the requested data size was received?
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No, according to the manual:
"Note that the TWI master does not stop by itself when the RAM buffer is full, or when an error occurs. The STOP task must be issued, through the use of a local or PPI shortcut, or in software as part of the error handler."
So i guess an alternative could be to add a PPI shortcut instead, like:
self.0.shorts.modify(|_r, w| w.lastrx_stop().enabled());
What do you prefer?
Thanks for your comments :)
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ok, this seems odd to me tbh, but I guess if the manual states this, it must be true :)
I think the short is cleaner but it also occupies a short slot which could be used by the user for another job. So I think we should leave it as is.
Issue #150