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fix #112

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Lotte Steenbrink 2021-01-29 15:04:51 +01:00
parent d202ff31d9
commit 111b5209c8
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embedded-workshop-book/src/get-descriptor-config.md
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@ -2,6 +2,16 @@
When the host issues a GET_DESCRIPTOR *Configuration* request the device needs to respond with the requested configuration descriptor *plus* all the interface and endpoint descriptors associated to that configuration descriptor during the DATA stage.
A GET_DESCRIPTOR Configuration request is a GET_DESCRIPTOR request where the descriptor type encoded in the high bit of `wValue` is CONFIGURATION.
As a reminder, all GET_DESCRIPTOR request types are share the following properties:
Let's look into all the concepts required to respond to this request.
- `bmRequestType` is **0b10000000**
- `bRequest` is **6** (i.e. the GET_DESCRIPTOR Request Code, defined in table 9-4 of the [USB specification][usb_spec])
A GET_DESCRIPTOR *Configuration* request is determined the high bit of its `wValue` field:
- The high bit of `wValue` is **2** (i.e. the `CONFIGURATION` descriptor type, defined in table 9-5 of the [USB specification][usb_spec])
[usb_spec]: https://www.usb.org/document-library/usb-20-specification
In the next sections, let's look into all the concepts required to respond to this request.