XMOS VocalFusion XVF3510, Руководство пользователя

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XM-014232-PC 34
4.3.2. USB HID
A Human Interface Device (HID) is an electronic device with an interface which a human can use for
control. Examples include a Personal Computer with a keyboard and mouse or a consumer appliance
with control knobs, push buttons or a voice interface.
The XVF3510-UA uses the HID interface to inform the host system of events which have occurred on
the General Purpose Inputs (GPI). The following section describes the setup of the GPI HID triggers.
HID REPORT GENERATION
The XVF3510 is able to send HID reports when an interrupt (logic edge transition event) on a GPI pin
has been received. When interrupts are enabled using
SET_GPI_INT_CONFIG
, the interrupt bit is
automatically serviced by the HID report generator. If an interrupt has occurred, then the sticky bit is
immediately cleared and an HID report is generated. The HID features are described below:
}
HID report for the assertion of GPI pin (positive edge) and report for the de-assertion (negative
edge)
}
The HID report type is generated with one of the following standard USB HID keycodes:
-
GUI Application Control Search (0x221)
-
GUI Application Control Stop (0x226)
-
Keyboard F23 (0x72)
-
Keyboard F24 (0x73)
}
When no event has occurred, depending on “set idle” configuration by the host, it will either
reply with a de-assert report (default) or NAK (set to idle by the host)
NOTE: HID idle behaviour is platform-specific and rarely the high-level application code will have any
control over the settings. Linux, for example, typically silences the devices by issuing an indefinite idle
(NAK report if no change). Other platforms such as MacOS, on the other hand, leave the device
verbose by not issuing an idle (report always sent).
The HID function requires that a GPI pin is configured to generate interrupts on both edges.
The HID Report Descriptor used in XVF3510-UA translates the GPI pin interrupt into a HID Report
asserting one of the predefined usages.
The HID Report has the format:
BIT 7 6 5 4 3 2 1 0
F24 F23 AC Stop AC Search Reserved
The corresponding bit equals 1 when a positive edge interrupt has been detected and zero where a
negative edge interrupt has occurred. In order to configure the GPI pin that triggers the HID report,
the SET_GPI_INT_CONFIG command is used.
For example, the following command configures GPI pin 0 to generate interrupts on both edges, which
enables the HID report logic:
vfctrl_usb SET_GPI_INT_CONFIG 0 0 3
The first argument is a reserved value and should be set to 0. The second argument makes the
command target pin IP_0. The third argument selects both edges for the interrupt. To make the device
respond to the falling edge only with the value 1 and rising edge only with the value 2.