register accessor layer and SPI support

[FoamyGuy]

Only SPI is implemented right now, I'll work on I2C next.

Adds new RegisterAccessor classes which RWBits and RWBit use so that they are agnostic to bus type.

I have successfully tested with a development version of the bmp5xx driver. I'll submit a PR over in that repo soon with the driver that relies on this new functionality.

Marking this draft until I2C is implemented, but wanted to get it opened now for any feedback.

[tannewt]

Thanks for the draft PR. This is definitely the right direction.

[FoamyGuy]

I found that the OV5640 camera module has I2C interface with 2 byte register addresses. I was able to successfully test the current version from this PR branch with this code.

import board
import busio
import digitalio
from adafruit_bus_device.i2c_device import I2CDevice
from adafruit_register.register_accessor import I2CRegisterAccessor
from adafruit_register.register_bits import ROBits, RWBits

I2C_ADDRESS = 0x3C
REG_CHIP_ID_HIGH = 0x300A

class OV5640Tester():
    chip_id = ROBits(16, REG_CHIP_ID_HIGH, 0, register_width=2, lsb_first=False)

    def __init__(self, i2c):

        try:
            i2c_device = I2CDevice(i2c, I2C_ADDRESS)
            self.register_accessor = I2CRegisterAccessor(i2c_device, address_width=2, lsb_first=False)
        except ValueError:
            raise ValueError(f"No I2C device found.")


if __name__ == '__main__':
    print("construct bus")
    i2c = busio.I2C(board.GP5, board.GP4)
    print("construct camera")
    reset = digitalio.DigitalInOut(board.GP14)

    ov5640 = OV5640Tester(i2c)
    print(hex(ov5640.chip_id))

[FoamyGuy]

Thank you. I got honed in on write_then_readinto() using the same buffer for both in/out in the existing implementation, overlooked that it can use different ones. That is quite convenient.

The latest commit removes the buffer concatenation and only uses _full_buffer() for i2c.write(). SPI write is split back into 2 writes now as well without concatenation.

I tested the latest version successfully with I2C & SPI on BMP5x & SPA06-003, and I2C / multi-byte address with OV5640. I submitted the latter as a new example to this repo as well.

[tannewt]

Thanks for iterating on this! I'm glad multibyte is working too.

[tannewt]

Same here, explain the protocol over I2C that this supports.

[tannewt]

Also talk about the relationship between address and data.

[FoamyGuy]

@tannewt All of those changes are made in the latest commit.

[tannewt]

One more minor doc thing. Do you want to undraft this PR?

[tannewt]

Also talk about the relationship between address and data.

[FoamyGuy]

Added more detail about the order of the addresses and data in the latest commit, and I've marked this ready now.

Thank you

[tannewt]

Ok, this will work. Thanks!