Hello People,
I am a desperate programmer trying to establish an SPI communication between my Arduino Mega 2560 and a PIC based device. I need to send my data as fletcher checksum and have implemented the coding for the same. Everything except the SPI bit seems to be working. I've gone through numerous blogs and I am still not able to put my finger on where am going wrong. My coding is as follows. Any help or suggestions will be highly appreciated.
Many thanks
Lallisan.
Coding:
#include <SPI.h>
const int slaveselect = 26;
byte tx_buf[9]; // [ Addr, len, d0, d1, .. c0, c1, dummy]
uint8_t total_len = 2;
void setup() {
// put your setup code here, to run once:
Serial.begin(115200);
digitalWrite(slaveselect, HIGH);
pinMode(slaveselect, OUTPUT); //SS
pinMode(52, OUTPUT); //SCLK
pinMode(50, OUTPUT); //MOSI
SPI.begin();
Serial.println("SPI communication has begun");
}
uint16_t fletcher16( uint8_t const *data, size_t bytes )
{
uint16_t sum1 = 0xff, sum2 = 0xff;
while (bytes) {
size_t tlen = bytes > 20 ? 20 : bytes;
bytes -= tlen;
do {
sum2 += sum1 += data++;
} while (--tlen);
sum1 = (sum1 & 0xff) + (sum1 >> 8);
sum2 = (sum2 & 0xff) + (sum2 >> 8);
}
/ Second reduction step to reduce sums to 8 bits */
sum1 = (sum1 & 0xff) + (sum1 >> 8);
sum2 = (sum2 & 0xff) + (sum2 >> 8);
return sum2 << 8 | sum1;
}
void fletcher_sum_data(uint8_t id, uint8_t address, uint8_t len, int32_t value)
{
int i;
tx_buf[0] = address;
tx_buf[1] = len;
while (len--)
{
tx_buf[total_len++] = value & 0xff;
value = value >> 8;
}
uint16_t csum;
uint8_t c0, c1, f0, f1;
csum = fletcher16( tx_buf, total_len); // total_len so far
f0 = csum & 0xff;
f1 = (csum >> 8) & 0xff;
c0 = 0xff - (( f0 + f1) % 0xff);
c1 = 0xff - (( f0 + c0 ) % 0xff);
tx_buf[total_len++] = c0;
tx_buf[total_len++] = c1;
tx_buf[total_len++] = 'D'; // Dummy byte
// total_len now includes c0, c1 and dummy.
/for (i = 0; i < total_len; i++)
{
Serial.println(tx_buf);*
_ }*/_
}
void loop() {
- // put your main code here, to run repeatedly:*
- int data;*
- int received_data;*
- int ch_no = 0;*
- int data_address = 0xC0;*
- int data_length = 2;*
- int data_value = 40;*
- fletcher_sum_data(ch_no, data_address, data_length, data_value);*
- for (data = 0; data < total_len; data++)*
- {*
- Serial.print("transmitted data: ");*
- Serial.println(tx_buf[data]);*
- digitalWrite(slaveselect, LOW);*
- received_data = SPI.transfer(tx_buf[data]);*
- Serial.println(received_data);*
- digitalWrite(slaveselect, HIGH);*
- delay(1000);*
- }*
}
