How to implement mutual exclusion for critical sections in code?

Hi @CarlosAM_INTEL ,

I am using Altera Cyclone V SOC Development kit. I have modified the example code provided alongwith namely,

Altera-SoCFPGA-HardwareLib-16550-CV-ARMCC:

The interrupt callback function that writes data into the buffer is modified as below:

volatile unsigned int tail = 0;

volatile unsigned int head = 0;

char buffer[ALT_16550_BUFFER_PROVISION_RX_BUFFER_SIZE];

void recieveData(ALT_16550_BUFFER_t * buffer1)

{

#if ALT_16550_BUFFER_ENABLE_SMP

/* Signal we are in the RX section. */

buffer1->isr_rx = true;

#endif

ALT_STATUS_CODE status = ALT_E_SUCCESS;

uint32_t fifo_level_rx;

uint32_t copy_size;

if (status == ALT_E_SUCCESS)

{

status = alt_16550_fifo_level_get_rx(buffer1->handle, &fifo_level_rx);

}

if (status == ALT_E_SUCCESS)

{

/* Copy the RX FIFO into the RX buffer. */

// alt_16550_int_disable_rx(buffer.handle);

// alt_int_global_disable_all();

// portCPU_IRQ_DISABLE();

const unsigned int tail_1 = tail;

const unsigned int head_1 = head;

// portCPU_IRQ_ENABLE();

if(head_1 < tail_1) {

copy_size = stdminul(fifo_level_rx,tail_1 - head_1);

}else{

copy_size = stdminul(fifo_level_rx,ALT_16550_BUFFER_PROVISION_RX_BUFFER_SIZE - head_1);

}

alt_16550_fifo_read(buffer1->handle,&(buffer[head_1]), copy_size);

// portCPU_IRQ_DISABLE();

head = (head_1 + copy_size) % ALT_16550_BUFFER_PROVISION_RX_BUFFER_SIZE;

// portCPU_IRQ_ENABLE();

// alt_int_global_enable_all();

// alt_16550_int_enable_rx(buffer.handle);

/* Disable RX interrupts if the RX buffer is full. */

/* if ((tail == 0) && (head == ALT_16550_BUFFER_PROVISION_RX_BUFFER_SIZE))

{

status = alt_16550_int_disable_rx(buffer1->handle);

}*/

}

}

The function in main that reads bytes from the buffer is given below:

char readBuffer() {

portCPU_IRQ_DISABLE();

const unsigned int tail_1 = tail;

const unsigned int head_1 = head;

portCPU_IRQ_ENABLE();

if(tail_1 == head_1) {

return NULL;

}

const char data = rxBuffer.buffer[tail_1];

portCPU_IRQ_DISABLE();

tail = (tail_1+1) % ALT_16550_BUFFER_PROVISION_RX_BUFFER_SIZE;

portCPU_IRQ_ENABLE();

// alt_int_global_enable_all();

// alt_16550_int_enable_rx(buffer.handle);

// alt_int_global_enable();

return data;

}

#define portCPU_IRQ_DISABLE() \

__asm volatile ( "CPSID i"); \

__asm volatile ( "DSB" ); \

__asm volatile ( "ISB" );

#define portCPU_IRQ_ENABLE() \

__asm volatile ( "CPSIE i"); \

__asm volatile ( "DSB" ); \

__asm volatile ( "ISB" );

I wish to protect access of tail and head. The interrupt function is receiving the whole data. But when we read from the buffer, some bytes are lost ( almost half).