RX and TX UART with NIOS2/e

Question

Hello all, i am beginner in NIOS2 programming and I try to use UART_0 in my system, where i have 22kB RAM on chip. So I have used the hello_world_small template. I tryed to blink with led, setting pio ports and sending with printf("hello world.
") text to jtag uart and read the jtag uart characters. (alt_getchar).  But i am not able to read and send the chars to uart_0, because i am not able to use fopen or open in this small model:  ---------------- like this ---------------------- char* msg = "Detected the character 't'.
"; FILE* fp; char prompt = 0; fp = fopen ("/dev/uart1", "r+"); //Open file for reading and writing if (fp) { while (prompt != 'v')  {  // Loop until we receive a 'v'. prompt = getc(fp);  // Get a character from the UART. if (prompt == 't') {  // Print a message if character is 't'. fwrite (msg, strlen (msg), 1, fp); } } fprintf(fp, "Closing the UART file.
"); fclose (fp); } return 0;  How can I read UART_0 and write to UART_0 ? I tryed to find some examples on alterawiki, but without succesfull.  Thank you very much.  Jan Naceradsky, Czech Republic

altera_forum · Answer

Personally I'd look at the register definition for the UART and write a function to add bytes to the fifo.

You then have to make a concious decision about what to do when the tx fifo is full.

Either:

- spin waiting for space.

- tell caller how many bytes were written (who might ignore the error).

You might decide it is worth adding a software fifo, but a large hardware fifo has much the same effect.

If you do use a software fifo, you don't necessarily need to use interupts - provided the software can poll the hardware often enough.

The same is true of receive - make the hardware fifo big enough.

I don't know if the uart can share an internal memory block between its rx and tx sides.

It also ought to be possibly to design a multi-port uart that uses a single memory block.

altera_forum · Answer

I used two file pointers : one for Transmit and one for receive

altera_forum · Answer

I would give the alt_stdio functions a try. Read about them in the docs...and there should be some examples as well.

altera_forum · Answer

Yes, i can use the functions:

alt_printf()

alt_putchar()

alt_putstr()

alt_getchar()

they work with stdin,stdout, but how can i change this standard i/o from jtag uart to uart_0 ?

And in additionally, when i tryed getchar function, it waits for RETURN. How can i make this, when i need to read the binary message from uart ?

Thank you very much.

Jan

altera_forum · Answer

Hi all,  I finally found some examples and make program, which work - it sends 4 bytes via uart0 and receives max.16 bytes via uart0. It works in hello world small template and when i compile, it take only 1852bytes (i run this on DE0_NANO development board). -------------------------------------------------- # include &lt;stdio.h&gt; # include &lt;unistd.h&gt; # include &lt;fcntl.h&gt; # include "sys/alt_stdio.h" # include "system.h" # include "altera_avalon_pio_regs.h" # include "altera_avalon_uart_regs.h" # include "altera_avalon_uart.h"  // global variables int count = 0,ch,n,status,led=0xff; int rx_cnt,rx_buf[16];  int main() {     alt_printf("1.Hello from Nios II!
");      while(1)     {   // printf("Hello from Nios II!
");         IOWR_ALTERA_AVALON_PIO_DATA(DATA_BUS_BASE, count );         IOWR_ALTERA_AVALON_PIO_DATA(LED_BASE, count);         count++;                  // send 4 bytes via UART0 (with waiting 100us)         IOWR_ALTERA_AVALON_UART_TXDATA(UART_0_BASE,0xFF);         usleep(100);         IOWR_ALTERA_AVALON_UART_TXDATA(UART_0_BASE,0xAA);         usleep(100);         IOWR_ALTERA_AVALON_UART_TXDATA(UART_0_BASE,count/256);         usleep(100);         IOWR_ALTERA_AVALON_UART_TXDATA(UART_0_BASE,count%256);         usleep(100);          // read bytes from UART and wait 20ms         rx_cnt=0;         for(n=0;n&lt;1000;n++)         {  usleep(20);            ch = IORD_ALTERA_AVALON_UART_STATUS(UART_0_BASE);            // if received some byte, read it            if ((ch&amp;0x80)==0x80)            {   ch = IORD_ALTERA_AVALON_UART_RXDATA(UART_0_BASE);                rx_buf[rx_cnt]= ch;                rx_cnt++;            }         }          // print the bytes to terminal         if (rx_cnt&gt;0)         {  alt_printf("rx_data:");            for(n=0;n&lt;rx_cnt;n++)            {  alt_printf("%x ",rx_buf[n]);            }            alt_printf("
");         }      }     return 0; } ------------------------  Jan Naceradsky, Czech Republic

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RX and TX UART with NIOS2/e

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