How to optimize the code for reading SPI through ARDUINO in SLAVE mode - optimization

Question

Not important:
I am doing a project to integrate a bluetooth module into a car radio pioneer. I understand perfectly well that it's easier to buy a new one =) but it's not interesting. At the moment, the byproduct was an adapter on arduino of resistor buttons, which the pioneer did not understand. The same adapter also controls the bluetooth board, it can switch the track forward and backward (there is no button on the steering wheel for pause). Now I want the bluetooth to turn on only in AUX mode. But there is a problem, which mode can be understood only by reading the signal from the SPI bus of the commutation microcircuit. I was able to read this data using arduino nano. I do not have an analyzer, but it is not necessary that I would understand something additional with it.
Essence of the question:
Using the scientific poke method, I found sequences indicating the launch of a particular mode, for example:
10110011
1
111
1000000
I'm sure I'm doing it wrong, but in the meantime I get duplicate results. But, when I try to detect them using IF, the nano speed is not enough and the chip starts to pass data.
#include "SPI.h"
bool flag01, flag02, flag03, flag11, flag12, flag13, flag31, flag32, flag33;
void setup (void)
{
Serial.begin(9600);
pinMode(MISO, OUTPUT);
SPCR |= _BV(SPE);
SPI.attachInterrupt();
}
// Вызываем функцию обработки прерываний по вектору SPI
// STC - Serial Transfer Comlete
ISR(SPI_STC_vect)
{
// Получаем байт из регистра данных SPI
byte c = SPDR;
Serial.println(c, BIN);
if (c == 0b1) {
Serial.println("1 ok");
flag11 = true;
} else {
flag11 = false;
}
if (c == 0b11 && flag11) {
Serial.println("11 ok");
flag12 = true;
} else {
flag12 = false;
flag11 = false;
}
if (c == 0b1100000 && flag11 && flag12) {
Serial.println("1100000 ok");
flag13 = true;
} else {
flag13 = false;
flag12 = false;
flag11 = false;
}
}
void loop(void)
{}
I myself am scared to look at this code, but I cannot think of anything better. It seems like I heard about some kind of buffer, but I don't know how to screw it to this solution. After all, the data packets go with dropping the CS signal and I can’t figure out how to determine the beginning and end of the packet from the commands in order to write it to a buffer or array and only then go through it with a comparison.
I will be grateful if someone will tell me at least in which direction to move.
There is also esp8266, but there is a limitation on the size of a data packet of 32 bits in a slave mode and I do not know how to get around it correctly.
So, actually the question.
How can I optimize the code so that the arduino has time to process the data and I can catch the pattern?
Perhaps, if we implement reading of data of arbitrary length on esp8266, or at least fill them to the required length, it would help me. But I still can't figure it out with the spi.slave library.

Answer 1

First you should keep your ISR as short as possible, certainly don't use Serial print inside the ISR.
Secondly, if you don't know exactly how long the data is, then you need to have a buffer to capture the data and try to determine the data length first before you trying to analysis it.
volatile uint8_t byteCount = 0;
volatile bool dataReady = false;
byte data[32];
// SPI interrupt routine
ISR (SPI_STC_vect)
{
data[byteCount++] = SPDR;
dataReady = true;
}
void setup (void)
{
// your SPI and Serial setup code
}
void loop (void)
{
// for determine the data stream length
if (dataReady) {
Serial.println(byteCount);
dataReady = false;
}
}
Once you know how long the data stream is (let assumed it is 15-byte long), you can then change your sketch slightly to capture the data and analysis it.
volatile uint8_t byteCount = 0;
volatile bool dataReady = false;
byte data[32];
// SPI interrupt routine
ISR (SPI_STC_vect)
{
data[byteCount++] = SPDR;
if (byteCount == 15)
dataReady = true;
}
void loop (void)
{
if (dataReady) {
dataReady = false;
// do your analysis here
}
}