add alt text

embedded-workshop-book/src/configuration-descriptor.md

@@ -1,7 +1,11 @@
 # Configuration descriptor
 
 <p align="center">
-  <img src="/usb-configuration.svg" alt="TODO">
+  <img src="/usb-configuration.svg" alt="USB hierarchy diagram showing the relationship between configurations, interfaces and endpoints. The diagram consists of nested rectangles. In this version of the diagram the 'configuration 1' rectangle and the 'bNumInterface' label are highlighted in blue.
+The outermost rectangle is labeled 'device' and represents the complete USB device.
+Inside the 'device' rectangle there is one rectangle labeled 'configuration 1'; this rectangle has a 'parallel lines' symbol that indicates there may be more than one configuration instance; the symbol is labeled 'bNumConfigurations=1' indicating that this device has only one configuration.
+Inside the 'configuration 1' rectangle there are two rectangles labeled 'control endpoint' and 'interface 0'. Inside the 'control endpoint' rectangle there are two rectangles labeled 'endpoint 0 IN' and 'endpoint 0 OUT. The 'interface 0' rectangle has a 'parallel lines' symbol that indicates there may be more than one interface instance; the symbol is labeled 'bNumInterfaces=1' indicating that this configuration has only one interface.
+Inside the 'interface 0' rectangle there are three rectangles labeled 'endpoint 1 IN', 'endpoint 2 IN' and 'endpoint 2 OUT'. Between these three rectangle there is a label that says 'bNumEndpoints=3'; it indicates that this interface has only three endpoints.">
 <p>
 
 The configuration descriptor describes one of the device configurations to the host. The descriptor contains the following information about a particular configuration:

embedded-workshop-book/src/control-transfers.md

@@ -1,7 +1,11 @@
 # Control Transfers
 
 <p align="center">
-  <img src="/usb-control.svg" alt="TODO">
+  <img src="/usb-control.svg" alt="USB hierarchy diagram showing the relationship between configurations, interfaces and endpoints. The diagram consists of nested rectangles. In this version of the diagram the 'control endpoint' rectangle is highlighted in blue.
+The outermost rectangle is labeled 'device' and represents the complete USB device.
+Inside the 'device' rectangle there is one rectangle labeled 'configuration 1'; this rectangle has a 'parallel lines' symbol that indicates there may be more than one configuration instance; the symbol is labeled 'bNumConfigurations=1' indicating that this device has only one configuration.
+Inside the 'configuration 1' rectangle there are two rectangles labeled 'control endpoint' and 'interface 0'. Inside the 'control endpoint' rectangle there are two rectangles labeled 'endpoint 0 IN' and 'endpoint 0 OUT. The 'interface 0' rectangle has a 'parallel lines' symbol that indicates there may be more than one interface instance; the symbol is labeled 'bNumInterfaces=1' indicating that this configuration has only one interface.
+Inside the 'interface 0' rectangle there are three rectangles labeled 'endpoint 1 IN', 'endpoint 2 IN' and 'endpoint 2 OUT'. Between these three rectangle there is a label that says 'bNumEndpoints=3'; it indicates that this interface has only three endpoints.">
 <p>
 
 Before we continue we need to discuss how data transfers work under the USB protocol.

embedded-workshop-book/src/device-descriptor.md

@@ -1,7 +1,11 @@
 # Device Descriptor
 
 <p align="center">
-  <img src="/usb-device.svg" alt="TODO">
+  <img src="/usb-device.svg" alt="USB hierarchy diagram showing the relationship between configurations, interfaces and endpoints. The diagram consists of nested rectangles. In this version of the diagram the outermost 'device' rectangle and the 'bNumConfigurations' label are highlighted in blue.
+The outermost rectangle is labeled 'device' and represents the complete USB device.
+Inside the 'device' rectangle there is one rectangle labeled 'configuration 1'; this rectangle has a 'parallel lines' symbol that indicates there may be more than one configuration instance; the symbol is labeled 'bNumConfigurations=1' indicating that this device has only one configuration.
+Inside the 'configuration 1' rectangle there are two rectangles labeled 'control endpoint' and 'interface 0'. Inside the 'control endpoint' rectangle there are two rectangles labeled 'endpoint 0 IN' and 'endpoint 0 OUT. The 'interface 0' rectangle has a 'parallel lines' symbol that indicates there may be more than one interface instance; the symbol is labeled 'bNumInterfaces=1' indicating that this configuration has only one interface.
+Inside the 'interface 0' rectangle there are three rectangles labeled 'endpoint 1 IN', 'endpoint 2 IN' and 'endpoint 2 OUT'. Between these three rectangle there is a label that says 'bNumEndpoints=3'; it indicates that this interface has only three endpoints.">
 <p>
 
 After receiving a GET_DESCRIPTOR request during the SETUP stage the device needs to respond with a *descriptor* during the DATA stage.

embedded-workshop-book/src/endpoint-descriptor.md

@@ -1,7 +1,11 @@
 ## Endpoint descriptor
 
 <p align="center">
-  <img src="/usb-endpoint.svg" alt="TODO">
+  <img src="/usb-endpoint.svg" alt="USB hierarchy diagram showing the relationship between configurations, interfaces and endpoints. The diagram consists of nested rectangles. In this version of the diagram the endpoint rectangles inside the 'interface 1' rectangle are highlighted in blue.
+The outermost rectangle is labeled 'device' and represents the complete USB device.
+Inside the 'device' rectangle there is one rectangle labeled 'configuration 1'; this rectangle has a 'parallel lines' symbol that indicates there may be more than one configuration instance; the symbol is labeled 'bNumConfigurations=1' indicating that this device has only one configuration.
+Inside the 'configuration 1' rectangle there are two rectangles labeled 'control endpoint' and 'interface 0'. Inside the 'control endpoint' rectangle there are two rectangles labeled 'endpoint 0 IN' and 'endpoint 0 OUT. The 'interface 0' rectangle has a 'parallel lines' symbol that indicates there may be more than one interface instance; the symbol is labeled 'bNumInterfaces=1' indicating that this configuration has only one interface.
+Inside the 'interface 0' rectangle there are three rectangles labeled 'endpoint 1 IN', 'endpoint 2 IN' and 'endpoint 2 OUT'. Between these three rectangle there is a label that says 'bNumEndpoints=3'; it indicates that this interface has only three endpoints.">
 <p>
 
 We will not need to deal with endpoint descriptors in this workshop but they are specified in section 9.6.6, Endpoint, of the USB specification.

embedded-workshop-book/src/interface-descriptor.md

@@ -1,7 +1,11 @@
 ## Interface descriptor
 
 <p align="center">
-  <img src="/usb-interface.svg" alt="TODO">
+  <img src="/usb-interface.svg" alt="USB hierarchy diagram showing the relationship between configurations, interfaces and endpoints. The diagram consists of nested rectangles. In this version of the diagram the 'interface 0' rectangle and the 'bNumEndpoints' label are highlighted in blue.
+The outermost rectangle is labeled 'device' and represents the complete USB device.
+Inside the 'device' rectangle there is one rectangle labeled 'configuration 1'; this rectangle has a 'parallel lines' symbol that indicates there may be more than one configuration instance; the symbol is labeled 'bNumConfigurations=1' indicating that this device has only one configuration.
+Inside the 'configuration 1' rectangle there are two rectangles labeled 'control endpoint' and 'interface 0'. Inside the 'control endpoint' rectangle there are two rectangles labeled 'endpoint 0 IN' and 'endpoint 0 OUT. The 'interface 0' rectangle has a 'parallel lines' symbol that indicates there may be more than one interface instance; the symbol is labeled 'bNumInterfaces=1' indicating that this configuration has only one interface.
+Inside the 'interface 0' rectangle there are three rectangles labeled 'endpoint 1 IN', 'endpoint 2 IN' and 'endpoint 2 OUT'. Between these three rectangle there is a label that says 'bNumEndpoints=3'; it indicates that this interface has only three endpoints.">
 <p>
 
 The interface descriptor describes one of the device interfaces to the host. The descriptor contains the following information about a particular interface:

embedded-workshop-book/src/interfaces.md

@@ -3,7 +3,11 @@
 We have covered configurations and endpoints but what is an *interface*?
 
 <p align="center">
-  <img src="/usb-interface.svg" alt="TODO">
+  <img src="/usb-interface.svg" alt="USB hierarchy diagram showing the relationship between configurations, interfaces and endpoints. The diagram consists of nested rectangles. In this version of the diagram the 'interface 0' rectangle and the 'bNumEndpoints' label are highlighted in blue.
+The outermost rectangle is labeled 'device' and represents the complete USB device.
+Inside the 'device' rectangle there is one rectangle labeled 'configuration 1'; this rectangle has a 'parallel lines' symbol that indicates there may be more than one configuration instance; the symbol is labeled 'bNumConfigurations=1' indicating that this device has only one configuration.
+Inside the 'configuration 1' rectangle there are two rectangles labeled 'control endpoint' and 'interface 0'. Inside the 'control endpoint' rectangle there are two rectangles labeled 'endpoint 0 IN' and 'endpoint 0 OUT. The 'interface 0' rectangle has a 'parallel lines' symbol that indicates there may be more than one interface instance; the symbol is labeled 'bNumInterfaces=1' indicating that this configuration has only one interface.
+Inside the 'interface 0' rectangle there are three rectangles labeled 'endpoint 1 IN', 'endpoint 2 IN' and 'endpoint 2 OUT'. Between these three rectangle there is a label that says 'bNumEndpoints=3'; it indicates that this interface has only three endpoints.">
 <p>
 
 An interface is closest to a USB device's function. For example, a USB mouse may expose a single HID (Human Interface Device) interface to report user input to the host. USB devices can expose multiple interfaces within a configuration. For example, the nRF52840 Dongle could expose both a CDC ACM interface (AKA virtual serial port) *and* a HID interface; the first interface could be used for (`log::info!`-style) logs; and the second one could provide a RPC (Remote Procedure Call) interface to the host for controlling the nRF52840's radio.

embedded-workshop-book/src/usb-endpoints.md

@@ -1,7 +1,11 @@
 # USB Endpoints
 
 <p align="center">
-  <img src="/usb-all-endpoints.svg" alt="TODO">
+  <img src="/usb-all-endpoints.svg" alt="USB hierarchy diagram showing the relationship between configurations, interfaces and endpoints. The diagram consists of nested rectangles. In this version of the diagram all the endpoint rectangles are highlighted in blue.
+The outermost rectangle is labeled 'device' and represents the complete USB device.
+Inside the 'device' rectangle there is one rectangle labeled 'configuration 1'; this rectangle has a 'parallel lines' symbol that indicates there may be more than one configuration instance; the symbol is labeled 'bNumConfigurations=1' indicating that this device has only one configuration.
+Inside the 'configuration 1' rectangle there are two rectangles labeled 'control endpoint' and 'interface 0'. Inside the 'control endpoint' rectangle there are two rectangles labeled 'endpoint 0 IN' and 'endpoint 0 OUT. The 'interface 0' rectangle has a 'parallel lines' symbol that indicates there may be more than one interface instance; the symbol is labeled 'bNumInterfaces=1' indicating that this configuration has only one interface.
+Inside the 'interface 0' rectangle there are three rectangles labeled 'endpoint 1 IN', 'endpoint 2 IN' and 'endpoint 2 OUT'. Between these three rectangle there is a label that says 'bNumEndpoints=3'; it indicates that this interface has only three endpoints.">
 <p>
 
 Under the USB protocol data transfers occur over *endpoints*.
@@ -11,7 +15,11 @@ Endpoints are similar to UDP or TCP ports in that they allow logical multiplexin
 Endpoints are identified by their address, a zero-based index, and direction. There are four types of endpoints: control endpoints, bulk endpoints, interrupt endpoints and isochronous endpoints. Each endpoint type has different properties: reliability, latency, etc. In this workshop we'll only need to deal with control endpoints.
 
 <p align="center">
-  <img src="/usb-control.svg" alt="TODO">
+  <img src="/usb-control.svg" alt="USB hierarchy diagram showing the relationship between configurations, interfaces and endpoints. The diagram consists of nested rectangles. In this version of the diagram the 'control endpoint' rectangle is highlighted in blue.
+The outermost rectangle is labeled 'device' and represents the complete USB device.
+Inside the 'device' rectangle there is one rectangle labeled 'configuration 1'; this rectangle has a 'parallel lines' symbol that indicates there may be more than one configuration instance; the symbol is labeled 'bNumConfigurations=1' indicating that this device has only one configuration.
+Inside the 'configuration 1' rectangle there are two rectangles labeled 'control endpoint' and 'interface 0'. Inside the 'control endpoint' rectangle there are two rectangles labeled 'endpoint 0 IN' and 'endpoint 0 OUT. The 'interface 0' rectangle has a 'parallel lines' symbol that indicates there may be more than one interface instance; the symbol is labeled 'bNumInterfaces=1' indicating that this configuration has only one interface.
+Inside the 'interface 0' rectangle there are three rectangles labeled 'endpoint 1 IN', 'endpoint 2 IN' and 'endpoint 2 OUT'. Between these three rectangle there is a label that says 'bNumEndpoints=3'; it indicates that this interface has only three endpoints.">
 <p>
 
 All USB devices must use "endpoint 0" as the default control endpoint. "Endpoint 0" actually refers to two endpoints: endpoint 0 IN and endpoint 0 OUT. This endpoint pair is used to establish a *control pipe*, a bidirectional communication channel between the host and device where data is exchanged using a predefined format. The default control pipe over endpoint 0 is mandatory: it must always be present and must always be active.