Our APIs are still immature and in heavy development. As we and others use them we discover aspects that are confusing or hard to use. We are correcting these problems now even though it breaks some code that uses the API, because there is currently very little code out there that depends on our API. Eventually we will publish a stable version but until then be aware that the API in our repository may change. We’ll announce any changes on this blog.
Users of our I2C API reported a few design flaws. The name of the I2CBus class was confusing: because there is only one I2C bus on the Pi, the name seemed to indicate that there could only be one instance of I2CBus active at any time. In fact it the class performs the master side of the I2C protocol on the bus. Many instances can be active at any time in different processes or even in the same process. So we have renamed it to I2CMaster.
The functions read, write and write_bytes in the quick2wire.i2c module were also confusingly named. They didn’t actually read or write but returned I/O actions that are performed by the I2CMaster.transaction method. We’ve renamed them to reading, writing and writing_bytes to make it more obvious that they don’t perform the I/O themselves.
So the I2C example program now looks like:
#!/usr/bin/env python3
from quick2wire.i2c import I2CMaster, writing_bytes, reading
import time
address = 0x20
iodir_register = 0x00
gpio_register = 0x09
with I2CMaster() as master:
master.transaction(
writing_bytes(address, iodir_register, 0xFF))
while True:
read_results = master.transaction(
writing_bytes(address, gpio_register),
reading(address, 1))
gpio_state = read_results[0][0]
print("%02x" % gpio_state)
time.sleep(1)
We’ve done the same in the SPI module as well to keep the two consistent.
There are likely to be further changes as we write classes to control our boards and other peripherals. But the APIs will settle down before long. We’ll keep you informed of any changes on this blog.