Avatar for Nadnerb


Member since Nov 2018 • Last active Jan 2019
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    Avatar for Nadnerb

    I was going through the Espruino Source code and noticed that the sleep uses WFE instead of WFI for the nrf52

    It was my understanding that WFI is typically used for standby and WFE is used for spinlocks. Just wondering what the benefit of using WFE is in this instance, and if we can get more power savings by using WFI if we are sleeping for a long period of time with an Interrupt wake-up source?

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    Avatar for Nadnerb

    I put together this implementation using a byte array without having to copy and allocate new strings.

    var buff = new Uint8Array(1024);
    //ascii string to byte array
    for (let i = 0; i < data.length; i++) {
          let c = ('0' + data.charCodeAt(i).toString(16)).slice(-­2);
          buff[i * 2] = c.charCodeAt(0);
          buff[i * 2 + 1] = c.charCodeAt(1);
    //Ascii string from byte Array - Note 'apply' only works for 64 arguments
    function fromByteArray(len) {
          if (len < 64) return String.fromCharCode.apply(String, buff.slice(0,len));
          for (var result = [], i = 0; i < len; i += 64) {
                result.push(String.fromCharCode.apply(St­ring, buff.slice(i, i + 64)));
          return result.join("").slice(0,len); 
    //Hex string to byte array
    function toByteArray(data) {
          for (let i = 0; i < data.length/2; i++) {
                buff[i] = parseInt((data.substring(i*2,i*2+2)),16)­
          buff.slice(0,data.length /2);

    After running a process.memory() command before and after these changes, I can't see any significant memory savings. Should we expect any improvements in memory usage by using a byte array, or does the string append provide the best use of memory allocation?

    What improvements could we make to this implementation to improve memory allocation?