XK-1A Development Board Tutorial

Before writing any code, you need a project to store your files in. To create a new project follow these steps:

The program below illuminates an LED on an XK-1A.

#include <xs1.h>

out port led = XS1_PORT_4F;

int main () {
  led <: 0b0001;
  while (1)
    ;
  return 0;
}

Copy and paste the code into your project, and then choose FileSave () to save your changes to file.

Take a look at the code in the editor. The declaration

out port led = XS1_PORT_4F;

declares an output port named led, which refers to the 4-bit port 4F. On the XK-1A, the I/O pins of port 4F are connected to the LEDs labeled LED0, LED1, LED2 and LED3.

Show image of port map...

XC input and output statements make it easy to express I/O operations on ports. The statement

led <: 0b0001;

causes the value specified to the right of <: to be output to the port specified to its left (led). The port then drives LED0 high and the other LEDs low, causing LED0 to illuminate yellow and the other LEDs to remain off.

The empty while loop prevents the program from terminating, which ensures that the LED remains illuminated.

To build and run your project, follow these steps:

To complete this part of the tutorial, perform the following steps:

The program below flashes a single LED on an XK-1A.

#include <xs1.h>

#define FLASH_PERIOD 20000000

out port led = XS1_PORT_4F;

int main (void) {
  timer tmr;
  unsigned isOn = 1;
  unsigned t;
  tmr :> t;
  while (1) {
    led <: isOn;
    t += FLASH_PERIOD;
    tmr when timerafter (t) :> void;
    isOn = !isOn;
  }
  return 0;
}

Copy and paste the code into your project, and then choose FileSave () to save your changes to file.

Take a look at the code in the editor. The declaration

timer tmr;

declares a variable named tmr, and allocates an available hardware timer. The L1 provides 10 timers, which can be used to determine when an event happens, or to delay execution until a particular time. Each timer contains a 32-bit counter that is incremented at 100MHz and whose value can be input at any time.

The statement

tmr :> t;

inputs the value of tmr‘s counter into the variable t. Having recorded the current time, the statement

t += FLASH_PERIOD;

increments this value by the required delay, and the statement

tmr when timerafter(t) :> void;

delays inputting a value until the specified time is reached. The input value is not needed, which is expressed as an input to void.

To build and run your project, follow these steps:

The Run button () can be used to switch between projects. To complete this part of the tutorial, follow these steps:

To complete this part of the tutorial, perform the following steps:

The program below inputs from one of two timers in a loop.

#include <xs1.h>

#define FLASH_PERIOD 10000000
#define CYCLE_PERIOD 50000000

out port led = XS1_PORT_4F;

int main (void) {
  timer tmrF, tmrC;
  unsigned timeF, timeC;

  tmrF :> timeF;
  tmrC :> timeC;
  while (1) {
    select {
      case tmrF when timerafter(timeF) :> void :
        /* add code to respond to timeout */
        break;
      case tmrC when timerafter(timeC) :> void :
        /* add code to respond to timeout */
        break;
    }
  }
  return 0;
}

Before continuing to the next part of this tutorial, create a new project using this code.

Take a look at the application code in the editor. The first statement in main inputs the value of the timer tmrF into the variable timeF, and the second statement inputs the value of the timer tmrC into the variable timeC.

In the while loop, the select statement waits for the an input on either tmrF or tmrC to become ready. It then performs the selected input and executes any code after it up until the keyword break.

If more than one input becomes ready at the same time, only one is executed in a single iteration of the loop; the other input is selected on the following iteration.

To complete this part of the tutorial, perform the following tasks:

To complete this part of the tutorial, perform the following tasks:

The program below creates two concurrent threads, which run two separate tasks independently of each other.

#include <xs1.h>
#include <stdio.h>

#define FLASH_PERIOD 10000000
#define CYCLE_PERIOD 50000000

out port led = XS1_PORT_4F;
in port but1 = XS1_PORT_1K;

void flashLEDs4bitPort(out port led, int flashPeriod, int cyclePeriod) {
  /* Code to flash 4 LEDs connected to a 4-bit port in a cycle */
  unsigned ledOn = 1;
  unsigned ledVal = 1;
  timer tmrF, tmrC;
  unsigned timeF, timeC;

  tmrF :> timeF;
  tmrC :> timeC;

  while (1) {
    select {
      case tmrF when timerafter(timeF) :> void:
        ledOn = !ledOn;
        if (ledOn)
          led <: ledVal;
            else
          led <: 0;
        timeF += FLASH_PERIOD;
        break;
      case tmrC when timerafter(timeC) :> void:
        ledVal <<= 1;
        if (ledVal == 0x10)
          ledVal = 1;
        timeC += CYCLE_PERIOD;
        break;
    }
  }
}

void respondToButton(in port but) {
  /* Code to respond to a button press */
 while (1) {
    but when pinseq(0) :> void;
    printf("Pressed\n");
    but when pinseq(1) :> void;
    printf("Released\n");
  }
}

int main(void) {
  par {
    flashLEDs4bitPort(led, FLASH_PERIOD, CYCLE_PERIOD);
    respondToButton(but1);
  }
  return 0;
}

Before continuing to the next part of this tutorial, create a new project using this code.

Take a look at the code in the editor. In main, the two statements inside the braces of the par are run concurrently: the current thread allocates a new hardware thread; the current thread then runs the function flashLEDs4bitPort; and the new thread runs the function respondToButton. The L1 device has a total of eight available hardware threads.

To complete this part of the tutorial, perform the following tasks:

A channel provides a synchronous, bidirectional link between two threads. It consists of two channel ends, which two threads can use to interact on demand using the XC input and output statements.

The program below creates two threads which are connected using a channel, and communicates a value over this channel.

void snd(chanend cout) {
  cout <: 1;
}

void rcv(chanend cin) {
  int x;
  cin :> x;
}

int main (void) {
  chan c;

  par {
    snd(c);
    rcv(c);
  }

  return 0;
}

The function snd declares a channel end parameter cout, which refers to one end of a channel. It uses the XC output statement to output the value 1 to a receiving thread.

The function rcv declares a channel end parameter cin and uses the XC input statement to input a value to the local variable x.

The function main declares a channel c. The locations of its two channel ends are established through its use in two statements of the par.

To complete this part of the tutorial, perform the following tasks:

This part of the tutorial shows you how to put ports and threads on different processor cores. It requires you to have two XK-1As available. Follow these steps: