Fix K20DX uart race condition #97
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Updated this PR to fix the KL26Z which has this problem as well. Also added a test to catch future regressions. The bug causing the echo test does not effect the atsam3u2c and lpc11u35 due to how the TX interrupt is enabled/disabled. The race condition causing TX count to get corrupted could not be reproduced in the atsam3u2c and lpc11u35. This PR does not comprehensively fix UART race conditions, since that would require an overhaul of each uart driver. Instead these are point fixes. |
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this might fix some problems what we have seen.. |
If a uart interrupt comes in at the right time then write_buffer.cnt_out can get incremented twice. This causes the TX interrupt to get stuck in a state where it is constantly transmitting data. This patch fixes that race condition by incrementing write_buffer.cnt_out in just one place - the uart interrupt.
When the mbed-os echo test runs it causes DAPLink to stop transmitting characters to the device. The echo test sends a string to the device, reads the same string back and then repeats this sequence. With optimizations in mbed-host-tests version 0.2.15 the repeat happens much faster, revealing this issue. This problem occurs because tx_in_progress is set to 1 in the middle of a a call to uart_write_data when UART1_RX_TX_IRQHandler is processing a UART RX interrupt. Because this flag is set, the function uart_write_data does not enable the transmitter interrupt as it should. This causes DAPLink to stop sending characters. This patch fixes this problem by checking that the write_buffer has data to send and enabling the transmitter interrupt in a critical section. It also prevents interrupts that aren't enabled from being processed to further avoid any race conditions. Finally, it removes tx_in_progress since this flag is no longer necessary.
Bring k20dx uart fixes into the kl26z: -Fix UART bug causing hang on echo test -Fix K20DX uart race condition
This patch adds a timing test which stress tests the UART by randomizing timing. The test is for catching race conditions in the uart, specifically when the uart finishes or starts sending data.
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This should fix #115 |
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If a uart interrupt comes in at the right time then
write_buffer.cnt_out can get incremented twice. This causes the TX
interrupt to get stuck in a state where it is constantly transmitting
data.
This patch fixes that race condition by incrementing
write_buffer.cnt_out in just one place - the uart interrupt.