Prevent starting a new I2C transmission before previous stop finishes. #737
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When a stop condition is generated by the I2C DMA callback, the code does not wait for the finish of the stop condition. If while the stop condition is being generated and a new I2C transaction attempts to start, the new transaction will be inadvertently terminated by the previous stop condition. Since ISRs should finish as quickly as possible, the ISRs should not spin-wait until the stop condition finishes. Instead, the spin-wait should be placed before starting a new transaction. The patch also removes incorrect comments that falsely indicate that the code will spin-wait until the stop condition finishes.
zyma98
changed the title
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Looks reasonable for me. cc @therealprof What do you think? |
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When a stop condition is generated by the I2C DMA (example), the code does not wait for the finish of the stop condition. However, the comments falsely indicate that there will be a spin-wait.
The I2C interface can get stuck if a new I2C transmission attempts to start while the previous stop condition is being generated. The new transaction will be inadvertently terminated by the previous stop condition. Subsequently, the I2C interface gets stuck. The following figure shows that a previous stop condition being generated can immediately terminate a new start condition, and after that the I2C interface is stuck.
Since ISRs should finish as quickly as possible, the fix should not let ISRs spin-wait in the interrupt handler until the stop condition finishes. Instead, the spin-wait should be placed before starting a new transmission.
The patch also removes incorrect comments that falsely indicate that the code will spin-wait until the stop condition finishes.