Bangle 2. How to set GPS Serial1 baud rate?

I tried CAS12 and got no response. And $GNGGA continue to be output. I would expect it to stop for 30 seconds using:

>cas12();
$PCAS12,30*2D
=undefined
$

I'd like to try the CASIC commands @fanoush - do you know if they are supported ?
I tried these but not sure if I have got the checksum calculation correct, its not a simple XOR.

function prt() {
  // CFG-PRT       cc       len        id       p  
  //            ---------  --------  ---------  ----
  print([0xBA,0xCE,0x00,0x00,0x06,0x00, 0x00, 0xd4,0x00,0x00,0x00]);
  Serial1.write([0xBA,0xCE,0x00,0x00,0x06,­0x00, 0x00, 0xd4,0x00,0x00,0x00]);
}

// ck = d4040000
function rate() {
  // CFG-PRT       cc       len        id       p  
  //            ---------  --------  ---------  ----
  print([0xBA,0xCE,0x00,0x00,0x06,0x04, 0x00, 0xd4,0x04,0x00,0x00]);
  Serial1.write([0xBA,0xCE,0x00,0x00,0x06,­0x04, 0x00, 0xd4,0x04,0x00,0x00]);
}

So far I am trying simple commands with 0 payload as it means the checksum is easier to calculate.

I have written this bit of code to do the first part of the calculation.

function ck(id,len,pl) {
  var clas = new Uint32Array(1);
  var i = new Uint32Array(1);
  var sum = new Uint32Array(1);

  clas[0] = 0xBACE;
  clas[0] = clas[0] << 24 ;

  i[0] = id;
  i[0] = i[0] << 16;

  //                       len     pl
  sum[0] = clas[0] + i[0] + len   + 0;
  print(sum[0].toString(16));
}