On 03/14/2014 04:11 PM, Stanislav Meduna wrote:
Hi,following scenario: - a Freescale i.MX28 machine - RS232 AUART looped back Rx - Tx or two different ports cross-connected - a test program sending data in one thread and receiving in the other: thread A periodically sends "Quick brown fox jumps over the lazy dog", thread B receives - stop the program using ctrl-C - restart => sometimes the receiving thread gets "dogQuick", receiving characters from the previous transmission The extra characters definitely come from the receiver - the transmission is OK. This was verified by a scope. My theory is that this behaviour is caused by mxs_auart_shutdown function gating and mxs_auart_startup reenabling the clock instead of doing a soft reset. If the clock is gated while the AUART already has something in the FIFO, but did not generate the interrupt yet, the internal state machine is frozen in this state. As soon as it is reenabled, the characters are delivered to a new user. I am using a 3.4.77 kernel, but the relevant code looks the same in the recent kernels (when not using DMA). I also backported patches waiting for the transmission FIFO to clear at mxs_auart_shutdown. I did not find any possibility to fully clear the receiver - even if one disables the AUART and reads everything from the FIFO, the character currently in transmit might be still somewhere (the reference manual states that disabling is effective after the current character is received). Which might be 1 ms at 9600 and one has no clue whether it is the case. Also note that the function mxs_auart_reset is in fact not doing a reset - it just makes sure that the AUART comes out of one after the initialization. Maybe a full reset at startup is the solution... Pleas Cc: me when answering.
Does disabling the fifo on shutdown clear the fifo? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
