delisoli.blogg.se - Interrupt based ser ail readingin python for mac os

#INTERRUPT BASED SER AIL READINGIN PYTHON FOR MAC OS SERIAL#
#INTERRUPT BASED SER AIL READINGIN PYTHON FOR MAC OS SOFTWARE#

Now we can use Python + LibUSB to send Control Endpoint packets with the commandĬtrl_transfer ( bmRequestType, bmRequest, wValue, wIndex, nBytes) This isn't surprising, motors are slow and don't require a lot of data to control.Ĭontrast this to the Video/Camera device:īInterfaceSubClass 255 Vendor Specific SubclassīInterfaceProtocol 255 Vendor Specific Protocolĭevice Qualifier (for other device speed): It just means it only uses a bidirectional Control Endpoint. This motor device has no Endpoints, but that doesn't mean you can't communicate with it.

#INTERRUPT BASED SER AIL READINGIN PYTHON FOR MAC OS SERIAL#

They're very 'cheap' to develop, and every device has one even if its not mentioned.įor example, a serial port may have two Interrupt endpoints for transferring data in and out and then a control endpoint for setting the baud rate.įor more details we really do suggest reading everything at about USB as it's complex. They are used to transfer small amounts of data to say turn a device on or off.

Control Endpoints are this weird not-quite-an-Endpoint Endpoint.

This endpoint goes only in one direction (so bidirectional audio for headphone and mic would have two EPs) This is for stuff like Audio and Video where timing is key.

Isochronous Endpoints are for transferring a fair amount of data where the data must show up at the same time and if it can't it should just be dropped.

In this case, the device has to be responsive so we want fast movement.

Interrupt Endpoints are for transferring tiny amounts of data very quickly, like for a USB mouse.

This endpoint goes only in one direction (so to read and write you'd want two) It's OK if it takes a little longer but we want big packets.

Bulk Endpoints are for transferring a lot of data, like a disk drive.

This means there are no Endpoints.Įndpoints are a type of USB 'data pipe' - there are 4 kinds:

Next we'll look at bNumConfigurations (how many different descriptors we have) and lucky for us the number is 1. Next, look at the Interface Descriptor in particular, bNumEndpoints which is 0. Today we're going to be reverse engineering the Xbox Kinect Motor, one part of the Kinect device.īDeviceClass 0 (Defined at Interface level)īInterfaceClass 255 Vendor Specific Class

#INTERRUPT BASED SER AIL READINGIN PYTHON FOR MAC OS SOFTWARE#

The good news is that every computer now made has a USB host core, that does a lot of the tough work for you, and there are many software libraries to assist. The bad news is it means you have to have software assistance to decode the complex packet structure. This is good for reverse engineering because it means that at least the format of packets is agreed upon and you won't have to deal with check-sums. Rather, data is bidirectional and differential - that is the data sent depends on the difference in voltage between the two data lines D+ and D- If you want to do more USB hacking, you'll need to read Jan Axelson's USB Complete books , they're easy to follow and discuss USB in both depth and breadth. USB uses only two wires but they are not used as 'receive' and 'transmit' like serial. USB is a very complex protocol, much more complicated than Serial or Parallel, SPI and even I2C. Everyone has seen the Xbox 360 Kinect hacked in a matter of days after our "open source driver" bounty - here's how we helped the winner and here's how you can reverse engineer USB devices as well!