Fix rare NRF52 serial TX lockup #8910
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When using UARTSerial sending data over the uart follows the sequence
below:
<-TX done ISR runs and sets a software interrupt to pending
<-Software interrupt fires:
-disables TX done interrupt
-calls UARTSerial TX handler which sends bytes until the uart
buffer filled (writeable returns false). Sending a byte
re-enables the TX done interrupt continuing the cycle
Due to this sequence, if the UARTSerial TX handler does not send a byte
then the transmit state machine mentioned above will get stuck with
the TX done interrupt disabled. The events causing this failure:
<-TX done ISR runs and sets a software interrupt to pending
<-Software interrupt fires:
-disables TX done interrupt
-calls UARTSerial TX handler:
-checks writeable which is true and sends a byte
<- interrupted by a higher priority interrrupt
<- TX done ISR runs, setting software interrupt to
pending again
-checks writeable which is true and sends a second byte
-Software interrupt finishes
<-Software interrupt fires:
-disables TX done interrupt
-calls UARTSerial TX handler:
-checks writeable which is false and DOES NOT SEND A BYTE
-Software interrupt finishes, the TX interrupt is still disabled
*-Byte gets sent but TX done ISR does not fire
This patch prevents the TX lockup by removing the code in the
software interrupt which disables the TX done interrupt. Disabling the
TX done interrupt at this point is not necessary so this code is safe
to remove.
kjbracey
approved these changes
Nov 30, 2018
0xc0170
approved these changes
Nov 30, 2018
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Description
When using UARTSerial to send serial data the uart NRF52 UART driver follows the sequence below:
Due to this sequence, if the UARTSerial TX handler does not send a byte then the transmit state machine mentioned above will get stuck with the TX done interrupt disabled. The events causing this failure:
This patch prevents the TX lockup by removing the code in the software interrupt which disables the TX done interrupt. Disabling the TX done interrupt at this point is not necessary so this code is safe to remove.
Pull request type