diff options
| -rw-r--r-- | usbdrv/usbconfig-prototype.h | 5 |
1 files changed, 3 insertions, 2 deletions
diff --git a/usbdrv/usbconfig-prototype.h b/usbdrv/usbconfig-prototype.h index 19369e0..488d776 100644 --- a/usbdrv/usbconfig-prototype.h +++ b/usbdrv/usbconfig-prototype.h @@ -166,8 +166,9 @@ section at the end of this file). * This macro (if defined) is executed in the assembler module when a * Start Of Frame condition is detected. It is recommended to define it to * the name of an assembler macro which is defined here as well so that more - * than one assembler instruction can be used. The macro may use registers - * YL and SREG. + * than one assembler instruction can be used. The macro may use the register + * YL and modify SREG. If it lasts longer than a couple of cycles, USB messages + * immediately after an SOF pulse may be lost and must be retried by the host. * What can you do with this hook? Since the SOF signal occurs exactly every * 1 ms (unless the host is in sleep mode), you can use it to tune OSCCAL in * designs running on the internal RC oscillator. |