everything is now documented

2018-01-25 22:23:10 +01:00
parent a44eb5f16a
commit 3784a46951
25 changed files with 387 additions and 82 deletions
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+USB support is implemented using the STM32 USB Device library.
+
+The library is copied into the core project to make customizations easier to maintain
+across different ports. The USBD library supports all versions of the HAL and LL.
+
+GEX uses USB classes CDC/ACM and MSC/SCSI.
+The two classes are combined into a composite class with association descriptors.
+
+USB interrupts are processed by the USBD library and endpoint callbacks in the composite
+class are fired. To avoid race conditions (and because DAPlink did it the same way), the
+events are notified to the USB thread (TaskMain) which calls endpoint handlers in the
+corresponding class drivers.
+
+VFS is handled synchronously on the main thread. CDC messages (TinyFrame data) are queued
+and processed by the message queue thread. This makes it possible to query hardware
+(e.g. slow USART or NeoPixel) without stalling the USB communication. This arrangement
+also makes it possible to wait on a binary semaphore when sending data back to host. The
+semaphore is set from the CDC TxComplete callback and taken by the TinyFrame write
+function, serving as a form of flow control.