Date: Fri, 26 Apr 2019 08:30:58 +0000 From: bugzilla-noreply@freebsd.org To: bugs@FreeBSD.org Subject: [Bug 237576] UART NS8250 parity and frame errors detection doesn't work Message-ID: <bug-237576-227@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=237576 Bug ID: 237576 Summary: UART NS8250 parity and frame errors detection doesn't work Product: Base System Version: CURRENT Hardware: Any OS: Any Status: New Severity: Affects Some People Priority: --- Component: kern Assignee: bugs@FreeBSD.org Reporter: smaryus@gmail.com On the UART NS8250 errors (parity/frame) are not detected when data is received because every time there is a read on LSR register the errors bit is removed. See [1] Current UART core implementation relies on the LSR register to detect if data is received. If data is received LSR is read again in pair with DATA register to determine if the received byte generate any errors. At this time LSR error bit is clear so no errors are reported. In code: 1. uart_core.c: `uart_intr()` calls `UART_IPEND` which will go into `ns8250_bus_ipend()`. Here LSR register is read and returns data received. 2. `uart_intr` calls `uart_intr_rxready` -> `UART_RECEIVE` -> `ns8250_bus_receive`. Here LSR is read again to check if the received byte generated error, but error bit from LSR is now 0. It was cleared by step 1. [1] https://en.wikibooks.org/wiki/Serial_Programming/8250_UART_Programming#Line_Status_Register -- You are receiving this mail because: You are the assignee for the bug.help
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