Commit 13c0db5

pbrookcmaglie

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Fix race condition in USB CDC transmit

If the Start of Frame interrupt triggers just after the call to USB_SendSpace in USB_Send then we can get data loss. When the first bank is full and the second partially full, the SOF handler will release the second bank via USB_Flush. Data is then lost due to overflow as USB_Send continues writing data to the now-closed bank. Fix this by re-checking the FIFO status inside LockEP, immediately before doing the data write. Signed-off-by: Paul Brook <paul@nowt.org>

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hardware/arduino/cores/arduino
- USBCore.cpp

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`‎hardware/arduino/cores/arduino/USBCore.cpp‎`

Lines changed: 4 additions & 1 deletion

Original file line number	Diff line number	Diff line change
`@@ -290,9 +290,12 @@ int USB_Send(u8 ep, const void* d, int len)`
`290`	`290`
`291`	`291`	`if (n > len)`
`292`	`292`	`n = len;`
`293`		`- len -= n;`
`294`	`293`	`{`
`295`	`294`	`LockEP lock(ep);`
	`295`	`+ // Frame may have been released by the SOF interrupt handler`
	`296`	`+ if (!ReadWriteAllowed())`
	`297`	`+ continue;`
	`298`	`+ len -= n;`
`296`	`299`	`if (ep & TRANSFER_ZERO)`
`297`	`300`	`{`
`298`	`301`	`while (n--)`

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Commit 13c0db5

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1 file changed

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`‎hardware/arduino/cores/arduino/USBCore.cpp‎`

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