RTEMS | bsps/arm/stm32f4: Add SPI bus driver (!1294)

Mon Jun 8 10:54:52 UTC 2026

Moksh Panicker commented on a discussion on bsps/arm/stm32f4/spi/spi.c: https://gitlab.rtems.org/rtems/rtos/rtems/-/merge_requests/1294#note_152110

 > +{
 > +  stm32f4_spi_bus      *bus  = arg;
 > +  volatile stm32f4_spi *regs = bus->regs;
 > +  uint32_t              sr   = regs->sr;
 > +
 > +  if (sr & STM32F4_SPI_SR_TXE) {
 > +    uint8_t byte = 0;
 > +    if (bus->tx_buf != NULL) {
 > +      byte = *bus->tx_buf++;
 > +    }
 > +    regs->dr = byte;
 > +    /*
 > +     * One byte is now in the shift register.  Disable TXE and wait
 > +     * for RXNE so we do not send another byte before the current one
 > +     * has been received (full-duplex, one byte in flight).
 > +     */

Good point, updated. The transfer now writes the first byte to DR directly, then uses only RXNE. Each received byte triggers writing the next TX byte immediately. TXE interrupt is no longer used.

-- 
View it on GitLab: https://gitlab.rtems.org/rtems/rtos/rtems/-/merge_requests/1294#note_152110
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