Sending Struct on SPI?

Another short article for embedded developers like me who are learning

We all use structures in our C / C++ programing most of the time and we also use spi bus as well

95% of the time we just use spi bus to communicate with some sort of sensor or peripheral on bus only receiving bytes which are very much presented to us in formalized and agreed upon structured data way

Like i am sending you byte and you reply me with a byte

What if i want to send a whole structure on spi bus which contains something like this

and my spi bus data register is only 8bit long how can i send a 32 bit unsigned integer with it and also a float etc,

is it even possible and lets say we are sending this data to some other microcontroller on pcb will it be able to receive it?

lets find a way to do it

Problem statement

we have both on sending and receiving side a buffer which is only 8bits long it can send and receive bytes perfectly and we want to send a struct which has all kind of data types so we need to serialize this struct into bytes

We need a memory in C which is 8 bits long in form of stack or array and contains the data our structure has

To get this memory we can use a union which is a shared memory we can put our struct in it and shape the union in form of byte arrays each element only 8bit long here is how we can do it

Then we can copy our data of struct into a union object like this

then we can simply type cast our union object into uint8_t pointer and send that to our spi bus

This is the result i get on my logic analyzer

It is accurate if we ignore the endianness of esp32 which is little endian chip

also don't forget to pack your struct otherwise you will be sending extra bytes of garbage values which is bad