User manual

USB interrupt results in a

USBHID_handleSendCompleted () event,

indicating the HID report has now been sent

bUsbSendCompleted flag is set to TRUE

USB event handlers

From within the USB API

USB interrupt results in new

MSC SCSI command received

Wake from LPM

The handler returns TRUE, waking the

device from LPM0 (if it was sleeping)

Port I/O ISR

Pushbutton is pressed

bButton1Pressed or

bButton1Pressed

flag is set to TRUE

www.ti.com

User Experience Software

Similarly, code checks for these other interrupt-driven events that may have occurred after the main loop

checked their flags. If execution enters sleep while these flags are set, they are not handled until yet

another interrupt occurs. This could cause the device to be unresponsive.

For similar reasons, interrupts are disabled prior to evaluating any of these flags. It takes several cycles to

evaluate these conditions, and because these events can occur at any time, the status of the early flags

could potentially change before LPM0 is actually entered. If LPM0 were then entered, they would get

missed. Disabling interrupts prevents that from happening; the events are simply queued up. When

interrupts are re-enabled, any interrupts that came in take effect immediately.

Therefore, the code simultaneously enters LPM0 and re-enables interrupts by setting the GIE bit:

_bis_SR_register(LPM0_bits + GIE);

If an interrupt had come in while interrupts were disabled, the CPU will wake again in the very next cycle

after entry.

3.5.6 LPM0 Exit

When emulating the code, if the device is sleeping, main() execution is seen resting at the LPM0 entry.

The demo application can then exit LPM0 and resume execution in response to three different events:

• A SCSI READ/WRITE command has been received. (This happens from a USB interrupt, which can

happen at any time.)

• A USB event has occurred. (This happens from the USB event handlers, which are triggered by USB

interrupts, which again can happen at any time.)

• One of the LaunchPad pushbuttons has been pressed.

Figure 30. Waking From LPM0

SLAU533A–September 2013–Revised January 2014 MSP430F5529 LaunchPad™ Development Tool (MSP

‑

EXP430F5529LP)

Submit Documentation Feedback