rtems_binary_semaphore_post from IRQ handler

[jameszxj]

From the document c-user.pdf 25.6.6，the funciton may be called from interrupt context. I have used rtems_semaphore_xxx API in UART drivers, it works fine.
RTEMS_FATAL_SOURCE_EXCEPTION should print the PC,LR ...
I think you can trace the PC pointer to see what makes the FATAL.




------------------ Original ------------------
From:  "Ярослав Лещински"<midniwalker at gmail.com>;
Date:  Sun, May 5, 2019 11:55 PM
To:  "users"<users at rtems.org>;

Subject:  Re: rtems_binary_semaphore_post from IRQ handler



Hello again,

still have some troubles with post/wait binary semaphore sequence. Could someone suggest what is a right way when you're working with semaphore inside interrupts.


I have sys call via spidev which is waiting for the binary semaphore. Semaphore released inside the interrupt. In some cases after several transmission I'm getting fatal: RTEMS_FATAL_SOURCE_EXCEPTION. 


I'll be really appreciate for any suggestions.


BRs, Yaroslav.



On Wed, 17 Apr 2019 at 16:25, Ярослав Лещинский <midniwalker at gmail.com> wrote:

Hello,

I wrote spidev driver for stm32l4 mcu.


spi_trasfer function looks like:


static int spi_transfer(
    spi_bus *base,
    const spi_ioc_transfer *msgs,
    uint32_t msg_count)
{
    struct stm32l4_spi_bus *bus = (struct stm32l4_spi_bus *)base;


    SPI_TypeDef *spix = (SPI_TypeDef *)bus->driver.spix;
    enum spi_major_num num = get_spi_major_number(spix);


    bus->msg = &msgs[0];
    spi_bus_table[num] = bus;
    spi_bus_table[num]->msg_count = msg_count;
    spi_bus_table[num]->messages_left = msg_count;


    int msg_error = spi_setup_trasfer(
            spi_bus_table[num],
            spi_bus_table[num]->msg,
            spi_bus_table[num]->messages_left);


    rtems_binary_semaphore_wait(&bus->sem);


    return (msg_error == 0)? 0 : -EINVAL;
}



Transmission proceeded via SPI IRQ + DMA IRQ. In DMA IRQ handler after dma successfully transmitted all data I'm using rtems_binary_semaphore_post for corresponding semaphore.


    bool bus_is_broken = (bus == NULL) ||
                         (msg_count < bus->messages_left) ||
                         (msg_count == 0);
    int ret = 0;


    if(bus_is_broken == true)
    {
        return -EINVAL;
    }


    if(msgs->cs_change == true)
    {
        spi_css_deselect(&bus->driver);
    }


    if(bus->messages_left > 0)
    {
        const size_t msg_idx = msg_count - bus->messages_left;
        ret = spi_do_transfer(bus, msgs, msg_idx);


        bus->messages_left--;


        if(ret != 0)
        {
            rtems_binary_semaphore_post(&bus->sem);


            return ret;
        }
    }
    else
    {
        rtems_binary_semaphore_post(&bus->sem);
    }


    return ret;



Currently I see that semaphore was successfully posted but control was not returned to spi_transfer.


As I know there are can be some issues with a context switching. Does rtems_binary_semaphore_post know about where control should be returned?




Thanks.


-- 
--
Kind regards,
Yaroslav Leshchinsky











 



-- 
--
Kind regards,
Yaroslav Leshchinsky
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