Re: Efficient Bit addressing in Python.

[Hendrik van Rooyen]

Ross Ridge wrote:

>This is the code I use to convert large bit arrays to byte strings and
back:

import string
import binascii
import array

8<--------------- examples ----------------------

>I don't think you can do anything faster with standard modules, although
it might not be efficient if you're only working with a single byte.

Thanks I was not aware of binascii module this looks powerful.

- Hendrik

[Ross Ridge]

Ross Ridge wrote:

>I don't think you can do anything faster with standard modules, although
it might not be efficient if you're only working with a single byte.

Hendrik van Rooyen <ma**@microcorp.co.zawrote:

>Thanks I was not aware of binascii module this looks powerful.

Not really. It's just used as part of a trick to quickly convert a byte
string in to a bit string (a byte string with just 0s and 1s).

Unfortunately fromr you other posts you do seem to be working on
a single byte a time, so my technique probably won't be efficient.
You probably want just want to be using constants and bit masking.
Something like:
PAC_EMERGENCY_STOP = 0x01 # bit #0 on output port 0
PAC_OUTPUT_0_1 = 0x02 # replace with names for other functions
PAC_OUTPUT_0_2 = 0x04
PAC_PNEUMATIC_PUSHER = 0x08 # bit #3 on output port 0
...

def gpio_bit_on(port, bit):
r = gpio_in(port)
r |= bit
r = gpio_out(port)

def gpio_bit_off(port, bit):
r = gpio_in(port)
r &= ~bit
r = gpio_out(port)

class pac(object):
def everything_off(self):
gpio_out(PAC_OUTPUT_PORT_0, 0)
gpio_out(PAC_OUTPUT_PORT_1, 0)
gpio_out(PAC_OUTPUT_PORT_2, 0)
...
gpio_out(PAC_OUTPUT_PORT_7, 0)

def emergency_stop(self):
gpio_bit_on(PAC_OUTPUT_PORT_0, PAC_EMERGENCY_STOP)

def pusher_on(self):
gpio_bit_on(PAC_OUTPUT_PORT_0, PAC_PNEUMATIC_PUSHER)

def pusher_off(self):
gpio_bit_off(PAC_OUTPUT_PORT_0, PAC_PNEUMATIC_PUSHER)
Bit twiddling like this is pretty basic.

Ross Ridge

--
l/ // Ross Ridge -- The Great HTMU
[oo][oo] rr****@csclub.uwaterloo.ca
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