Connecting multiple slaves with PcDuino SPI bus - spi

Question

I am currently working on a 3D-printer like project where I have to control 3 stepper drivers using SPI from a PcDuino. There a very few examples and only a bad documentation out there describing what I am looking for. It seems the preinstalled API does not support multiple slaves, but if I am understanding it correctly I just have to add more CS lines and control them my self?
Is there anything else to take care of and how long do I need to hold the CS low while sending or receiving data?
(Well I guess receiving is no problem as it is on another line anyway)

Answer 1

Turned out to be quiet easy:
Just have to select, transfer and deselect.
No sleep or waiting needed.
Select and deselect have to be done using the pin devices api,
so you can use as many slaves as you have free pins.
Example implementation:
void GPIOpin::set(FILE* fd, size_t value) {
char buffer[4];
memset(buffer, 0, 4);
sprintf(buffer, "%d", value);
fseek(fd, 0, SEEK_SET);
fwrite(buffer, 1, 4, fd);
fflush(fd);
}
bool SPI::transfer(size_t slaveIndex, uint8_t* buffer, uint64_t size) const {
if(!handle) return false;
struct spi_ioc_transfer transfer;
memset(&transfer, 0, sizeof(transfer));
transfer.len = 1;
for(size_t i = 0; i < size; ++i) {
slaveCS[slaveIndex].setValue(0);
transfer.tx_buf = transfer.rx_buf = (uint64_t)&buffer[i];
if(ioctl(handle, SPI_IOC_MESSAGE(1), &transfer) != transfer.len)
return false;
slaveCS[slaveIndex].setValue(1);
}
return true;
}
Complete code:
https://github.com/Lichtso/PrismCNC/tree/master/backend
Only difficulty: The master has to deselect and reselect the slave for each byte transferred. (but this could be a issue of the slave chips, not sure, just tested 3 different devices including an Arduino)