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Add comment of usb_cable_config.

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NIIBE Yutaka
2019-04-11 13:48:26 +09:00
parent 5a6910a45b
commit 8b9d2c007a
1 changed files with 9 additions and 0 deletions
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9
mcu/sys-stm32f103.c
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@@ -21,6 +21,15 @@
#include "mcu/clk_gpio_init-stm32f.c"
/*
* When a board supports USB self-powered configuration, there is a
* control to enable external pull-up 1K5 resistor. The voltage
* source on the pull-up resistor should be only supplied when VBUS
* from the cable is available. This routine is for such a board.
*
* For a board for USB bus-powered configuration, it is common that
* there is no such control, but 1K5 resistor is fixed to +3V3.
*/
static void
usb_cable_config (int enable)
{