drivers: usb: stm32: add support for incomplete isochronous in transfer #84622
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Hello @AlgotAxelzon, and thank you very much for your first pull request to the Zephyr project! |
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Implement the HAL callback function `HAL_PCD_ISOINIncompleteCallback` in which the endpoint write semaphore is given back, thus allowing subsequent writes to the endpoint after an isochronous transfer has been incompleted (not read by the host). This approach was chosen because it is similar to what is done in the already implemented HAL callback `HAL_PCD_DataInStageCallback` which also gives the write semaphore back but also calls the endpoint callback function. The reason for not also calling the endpoint callback function is because I do not see any appropriate cb_status (`enum usb_dc_ep_cb_status_code`) to pass. If passing `USB_DC_EP_DATA_IN` is okay even though "In transaction done on this EP" is not completely true, then this should also be added. This has been tested by setting up an isochronous endpoint, writing to it, and verify that `HAL_PCD_DataInStageCallback` is called and subsequent writes are possible. Signed-off-by: Algot Axelzon <[email protected]>
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Hi, I updated the commit message again. As stated in there I am unsure if the endpoint callback should be called or not. |
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Currently the
write_semfor an endpoint is only given back if the data was actually read by host (and thus callingHAL_PCD_DataInStageCallbackwherin the semaphore is given back).The problem that occurs is when you want to implement an isochronous endpoint that periodically writes data to the endpoint. As isochronous transfers are not supposed to have any guarantee of delivery it should be possible to send data again and again without a host having to read/receive them. With the current design this is not possible.
To solve this problem another HAL callback was implemented in a similar fashion to
HAL_PCD_DataInStageCallback. This other callback function is namedHAL_PCD_ISOINIncompleteCallback, and as its name suggests it is being called when data in an isochronous in endpoint has not been "delivered". So, in this callback the write semaphore is given back allowing for sequent writes.Please let me know if you have any input on this!