Serial discard line break #274
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Current version of write will never use the interrupt mode transmission, because it fails to check if holding register is empty. This commit fix that, and several (maybe not all) bugs related to interrupt mode serial transmission.
When possible, fill the tx FIFO in interrupt handler, in order to reduce number of interrupts called and overhead.
In case of line break, a 0x00 byte is added to the receive fifo. This commit change the irq handler to discard this data. Other LSR interrupt sources (overrun, parity or framing error) are ignored.
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I also have a question about the hardware implementation of the uart. From my experiments, it seems that when i disconnect the uart rx pin (using |
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| void UARTClass::flush( void ) | ||
| { | ||
| while (_tx_buffer->_iHead != _tx_buffer->_iTail); //wait for transmit data to be sent | ||
| while (_tx_buffer->_iHead != *(volatile int*)&(_tx_buffer->_iTail)); //wait for transmit data to be sent |
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Is there a particular reason for casting the pointer to a volatile pointer first prior to using it? Is the code being optimized out by the compiler if the volatile casting is omitted?
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The reason is that iTail can be updated in the irq handler.
Without the volatile, the compiler may optimize the code by reading it only once from memory, and keeping its value in register. That would lead to an infinite loop.
I don't remember if i actually ran into this problem or not, and i did not check the resulting assembly, but that looks like a typical case where volatile is needed.
Note that this more related to pull request #266 than to #274
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I will rebase this against #266 (when merged), and complete it with the parity and framing error cases, so put it on hold for now. |
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Released and merged with 266. |
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Enable the Receiver Line Status interrupt source in order to discard the 0x00 byte that is generated in case of line break.
I need this because i use the uart to implement a half duplex communication by connecting rx and tx together and enabling/disabling rx/tx. When i disable rx, a line break is generated, and a false data byte of 0x00 is read.
Maybe data shoud also be discarded in case of parity error and framing error?
This code is based on #266
Test case :
serial3_error.ino.txt