diff options
| -rw-r--r-- | chip/stm32/usb.c | 12 |
1 files changed, 9 insertions, 3 deletions
diff --git a/chip/stm32/usb.c b/chip/stm32/usb.c index 631dc8a19d..ff71b4e582 100644 --- a/chip/stm32/usb.c +++ b/chip/stm32/usb.c @@ -346,9 +346,15 @@ int usb_is_enabled(void) void *memcpy_to_usbram(void *dest, const void *src, size_t n) { - int i; - uint8_t *s = (uint8_t *) src; - usb_uint *d = (usb_uint *)((uintptr_t) dest & ~1); + /* + * The d pointer needs to be volatile to prevent GCC from possibly + * breaking writes to the USB packet RAM into multiple 16-bit writes, + * which, due to the way the AHB2APB bridge works would clobber what + * we write with 32-bit extensions of the 16-bit writes. + */ + int i; + uint8_t *s = (uint8_t *) src; + usb_uint volatile *d = (usb_uint volatile *)((uintptr_t) dest & ~1); if ((((uintptr_t) dest) & 1) && n) { /* |