Hello,

I understand that this is not the optimal way to perform such an action, but I'm in search of why it is not working still. I am aware of how to correctly use semaphores to utilize the resource. If I step through this while debugging, the uart outputs the string just fine. If I just let the task run though without any breakpoints, it seems to output the string characters at random ie: "tstesttses". It is my understanding that wrapping the putstring func with enter and exit critical or suspend and resume all should allow this action to take place uninterrupted. This is the only task running.

Thank you

I am using:

Chip: STM32F107VC (Cortex-M3)

Compiler: arm-none-eabi-gcc

Version: FreeRTOS V8.0.1

~~~~~~~

static void prvUARTTask( void *pvParameters ) {

/* Block for 500ms. */ const TickTypet xDelay = 50 / portTICKPERIOD_MS;

const uint8_t testString[] = "test";

for(;;) {

vTaskDelay( xDelay );

taskENTER_CRITICAL();
{
	USART_PutString(testString);
}
taskEXIT_CRITICAL();

} } ~~~~~~~

If USART_PutString() is using interrupts then you won't be able to put the call in a critical section. If that is the only task using the uart then a critical section isnt needed anyway.

Try without the critical section. If that doesnt fix the problem then it must be in the USART_PutString() function. Maybe it is writing a new character to the uart before the last one has been sent.

Thanks for the reply Dave.

I tried without the critical before of course, the critical was my attempt to rule out any interruptions. The putstring does not use interrupts, its just a simple write data to register func. I'm pretty puzzled by this.

I just simplified it even more

~~~~~ static void prvUARTTask( void *pvParameters ) {

/* Block for 500ms. */ const TickTypet xDelay = 50 / portTICKPERIOD_MS;

const uint8_t testString[] = "test";

for(;;) { vTaskDelay( xDelay );

USART1->DR = ('a' & (uint16_t)0x01FF);
USART1->DR = ('b' & (uint16_t)0x01FF);
USART1->DR = ('c' & (uint16_t)0x01FF);
USART1->DR = ('d' & (uint16_t)0x01FF);
USART1->DR = ('\n' & (uint16_t)0x01FF);

} } ~~~~~~~

and I get this output now: ~~~~~~

   d







        c







             b









                   d

~~~~~~

Not that it is anything to do with FreeRTOS, but unless there is a FIFO you will have to wait until one character has been transmitted before writing the next. If there is a FIFO then you will have to check the FIFO is not full before writing the next.

You probably have to wait for each char to actually go out… you’re probably overwriting them. To test, try putting a delay between each write to the UART register that’s greater than the time to TX a byte. M

On Dec 9, 2014, at 3:41 PMEST, k3nt k3nt00@users.sf.net wrote:

Thanks for the reply Dave.

I tried without the critical before of course, the critical was my attempt to rule out any interruptions. The putstring does not use interrupts, its just a simple write data to register func. I'm pretty puzzled by this.

I just simplified it even more

static void prvUARTTask( void *pvParameters ) {

/* Block for 500ms. */ const TickTypet xDelay = 50 / portTICKPERIOD_MS;

const uint8_t testString[] = "test";

for(;;) { vTaskDelay( xDelay );

USART1->DR = ('a' & (uint16_t)0x01FF);
USART1->DR = ('b' & (uint16_t)0x01FF);
USART1->DR = ('c' & (uint16_t)0x01FF);
USART1->DR = ('d' & (uint16_t)0x01FF);
USART1->DR = ('\n' & (uint16_t)0x01FF);

} } and I get this output now:

d

c

b

d

Simple UART Output not working correctly - Cortex-M3

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I'm using ST's std periph libs. It doesn't do any checking, it just writes to the register like above. This works perfectly fine of course without a scheduler so I'm just trying to understand why and if it is in fact related.

Thanks

I just recreated this without the freertos scheduler. Same results. My apologies. Thanks for your help!