Using SPI to send list

[martynwheeler]

Hi,

I am trying to port a function from python into upython. The function uses the spidev library in python which does not exist in upython.

here is the python function:

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    def _spi_write(self, register, payload):
        if type(payload) == int:
            payload = [payload]
        elif type(payload) == bytes:
            payload = [p for p in payload]
        elif type(payload) == str:
            payload = [ord(s) for s in payload]

        self.spi.xfer([register | 0x80] + payload)

xfer is described as

"Performs an SPI transaction. Chip-select should be released and reactivated between blocks. Delay specifies the delay in usec between blocks."

It is sending a list of two bytes in the function. In upython there is an spi.write method which sends a single byte. so can i simply loop over the list and use spi.write?

Thanks in advance,

Martyn

[Roberthh]

The spi.write method of MicroPython sends a buffer with as many bytes as are in the buffer. So you can send either each object independently, or pack them all into a buffer and send that one. For the sake of memory efficiency, I would go for the first option and encode and send the data directly in the if/elif/elif sequence of your same script.
- The int object has to be encoded in a suitable bytes object then be sent, e.g. with formatting: spi.write(b'%d' % payload)
- the byte object can be sent as it is: spi.write(payload)
- the str-object just has to be encoded to bytes and then sent: spi.write(payload.encode())

[martynwheeler]

Thanks, I will give it a go later.

[pythoncoder]

If you want exactly two bytes, for the integer I'd use

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self.spi.write(int.to_bytes(payload, 2, 'little'))

The 'little' or 'big' arg determines the order in which the bytes are transmitted.