Embedded

SVC will be pended if a higher priority exception arrives during the stacking. If the priority of SVC is raised above the previously higher priority exception inside its handler, SVC will be activated immediately, nested above the current handler, which causes problems because the register context seen by the SVC handler is not system call arguments.

Read-modify-write on the cr1 register of I²C may generate two consecutive start condition and hang the peripheral.

The Rust HAL Library stm32f4xx-hal failed to set the LAST bit in I²C CR2 before initiating a DMA read. We tracked down the problem with a logic analyzer and identified the fix.

The I²C bus may be stuck busy after a software reset if the slave peripheral is holding the SDA line upon reset. Manually generating some clock pulses on the SCL line and sending a NACK on the SDA line will make the peripheral to release the SDA line, allowing normal operation.

STM32F4xx I²C can be stuck after start condition when the stop bit is set while the I²C bus is already idle.

We discuss why 2-byte alignment is not sufficient for thumb2 instructions even though the ISA supports an arbitrary mixture of 2- and 4-byte instructions.