uBlox UBX checksum calculator

ubx_checksum.py

# CFG-RATE (0x06,0x08) packet (without header 0xB5,0x62)
# payload length - 6 (little endian format), update rate 200ms, cycles - 1, reference - UTC (0)
packet = [0x06,0x08, 0x06,0x00, 0x00,0xC8, 0x00,0x01, 0x00,0x00]

CK_A,CK_B = 0, 0
for i in range(len(packet)):
  CK_A = CK_A + packet[i]
  CK_B = CK_B + CK_A

# ensure unsigned byte range
CK_A = CK_A & 0xFF
CK_B = CK_B & 0xFF

print "UBX packet checksum:", ("0x%02X,0x%02X" % (CK_A,CK_B))

Hi,
i tried it on on the last command at this link

https://ukhas.org.uk/guides:ublox_psm

GPS Cold Start (Forced Watchdog)
0xB5, 0x62, 0x06, 0x04, 0x04, 0x00, 0xFF, 0x87, 0x00, 0x00, 0x94, 0xF5

it fails

it throws
0x94 0x1D instead of above 0x94 0xF5

not sure which is correct, can you please help

You are calculating it wrong. The checksum is calculated only from payload bytes, i.e.: 0x06, 0x04, 0x04, 0x00, 0xFF, 0x87, 0x00, 0x00
No header or checksum bytes are involved in calculation.

After running with your payload, the result is:
UBX packet checksum: 0x94,0xF5

#UBX packet checksum

hi that's code works:
I will give you my tested sample
(rust lang..)
fn main() {
let data =[ 0xB5,0x62,0x01, 0x07,0x54,0x00, 0xBC,0xB5,0x4B, 0x0B,0xE2,0x07, 0x06,0x05,0x04, 0x26,0x0D,0x07, 0x04,0x00,0x00, 0x00,0x8A,0xCA, 0xF7,0x05,0x03, 0x01,0x0A,0x0C, 0x97,0x4A,0x5A, 0x57,0xA0,0xD3, 0x3B,0xE9,0xF8, 0xD5,0x00,0x00, 0xC6,0xD8,0x00, 0x00,0x59,0x05, 0x00,0x00,0x1E, 0x07,0x00,0x00, 0x09,0x00,0x00, 0x00,0xDB,0xFF, 0xFF,0xFF,0xF5, 0xFF,0xFF,0xFF, 0x26,0x00,0x00, 0x00,0x70,0x85, 0x1B,0x01,0xF5, 0x00,0x00,0x00, 0x4A,0x28,0x50, 0x00,0x90,0x00, 0x00,0x00,0x84, 0xD3,0x11,0x00, 0x93,0x4F];

let mut CK_A = 0;
let mut CK_B = 0;
let len =data.len();

for i in 0..len {
if i == 0 || i == 1 || i == len-2 || i ==len-1{continue;}
CK_A = CK_A + data[i];
CK_B = CK_B + CK_A;
}
CK_A = CK_A & 0xFF;
CK_B = CK_B & 0xFF;

println!("{:#x}",CK_A);
println!("{:#x}",CK_B);
}

//AmirMahdi Hassanzadeh