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Hi all, I'm currently working in an application that requires the MCU to g
into deep sleep (LPM4) and wake up and process data on UART receive, an
then go back to LPM4. What is the right way to do this? I tried doing th
following as TI's guide Rev. E. suggests, but this crashes the MCU.
tried to debug the code but I just can't find where the problem is. Th
serial data is received using IR, in a constant stream that does not sto
until the "transmitter" is taken away from the receiver. This will wor
fine for a while but it eventually crashes.

What I've seen is that somehow when the software is busy handling a
interrupt, it STILL accepts other interrupts even when the GIE bit is off
Sometimes the instruction that sends the MCU back to active mode doesn't d
anything or messes everything up. I really need help here as I'm runnin
out of ideas. BTW, the problem is not on hardware, all of the require
pins are correctly terminated to either VCC or ground, even th
programming pins, reset, etc.


#include "msp430x12x.h"
;_______________________________________________________________________
; INTERRUPT VECTORS USED
;_______________________________________________________________________
ORG 0FFFEh ; power-up interrupt
DW RESET

ORG 0FFEEh ; USART0 receive interrupt
DW RECEIVE

;+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
; CODE
;+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
ORG 0F000h ; program start for MSP430F122
;___________________________
; Reset Interrupt sequence
;___________________________
RESET
MOV.W #0300h, SP ; initialize stack pointer
CALL #INIT ; initalize the UART

MAIN
BIS #LPM4+GIE, SR ; wait for start-edge
NOP ; Needed by debugger
CMP.B #f0, r8 ; check received data
JNZ MAIN ; incorrect data! jmp!
XOR.B #1, P1OUT ; toggle LED pin to ack received flag
JMP MAIN

;_______________________________________________________________________
; USART Interrupt sequence
;_______________________________________________________________________
RECEIVE
BIT.B #URXIFG0,&IFG2 ; Test URXIFGx to determine
JNZ StartRec ; If start-edge or character
; if IFG is set, Z=0, continue.
; if IFG not set (no complet
transmission), return!

StartEdge ; wake up and receive char
BIC.B #URXSE,&U0TCTL ; Clear URXS signal
BIS.B #URXSE,&U0TCTL ; Re-enable edge detect
BIC #SCG0+SCG1,0(SP) ; Enable BRCLK = DCO; CPU still off
JMP EndRcv

StartRec
MOV.B &U0RXBUF, r8 ; Save received char in r8
BIC #OE+FE+PE+RXERR,U0RCTL ;Clear any errors received
BIC #LPM4+GIE,0(SP) ; Char received, wake up and proces
data

EndRcv
RETI

;_______________________________________________________________________
; Initialization function (sets up UART, flags and interrupts)
;_______________________________________________________________________
INIT
MOV.W #WDTPW+WDTHOLD, &WDTCTL ; stop watchdog
BIS #OSCOFF, SR ; not using LFXTL1

//Initialize UART
BIS.B #CHAR, &U0CTL
; 1 stop bit
; 8-bit word
BIS.B #SSEL1, &U0TCTL ; use sub-main clock for UART (@750kHz)
MOV.B #RATIO, &U0BR0 ; f = 750kHz in MSP430F122
MOV.B #000h, &U0BR1 ;
MOV.B #00h, &U0MCTL ; receive moodulation set to zero; 0.0
is small
BIS.B #URXSE, &U0TCTL ; enable start-edge wake-up
BIS.B #020h, &P3SEL ; select P3.5 for serial reception
BIC.B #020h, &P3DIR ; and input
BIS.B #URXE0, &ME2 ; enable receiver (MSP430F122)
BIC.B #SWRST, &U0CTL ; clear UART software reset
BIS.B #URXIE0, &IE2 ; enable receiver interrupt
(MSP430F122)

BIS.B #003h, &P1DIR ; P1.1 and P1.0 output
BIS.B #003h, &P1OUT ; turn LEDs off

EINT ; enable interrupts: GIE<-1

RET

END





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In article <mtOdnTdj66Gi3BrfRVn_vg@giganews.com>, jerry_bp@hotmail.com
says...

Hi all, I'm currently working in an application that requires the MCU to go
into deep sleep (LPM4) and wake up and process data on UART receive, and
then go back to LPM4. What is the right way to do this? I tried doing the
following as TI's guide Rev. E. suggests, but this crashes the MCU. I
tried to debug the code but I just can't find where the problem is. The
serial data is received using IR, in a constant stream that does not stop
until the "transmitter" is taken away from the receiver. This will work
fine for a while but it eventually crashes.

What I've seen is that somehow when the software is busy handling an
interrupt, it STILL accepts other interrupts even when the GIE bit is off.
Sometimes the instruction that sends the MCU back to active mode doesn't do
anything or messes everything up. I really need help here as I'm running
out of ideas. BTW, the problem is not on hardware, all of the required
pins are correctly terminated to either VCC or ground, even the
programming pins, reset, etc.

IIRC, the LPM4 mode shuts off all the clocks, including that to the
UART. Are you sure that the UART clock is starting up quickly enough
to capture the start bit?

If the data is really received in a constant stream, you might be
better off not going into LPM4 mode after each character---but
only when no character has been received for a pre-determined
interval.

#include "msp430x12x.h"
;_______________________________________________________________________
; INTERRUPT VECTORS USED
;_______________________________________________________________________
ORG 0FFFEh ; power-up interrupt
DW RESET

ORG 0FFEEh ; USART0 receive interrupt
DW RECEIVE

;+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
; CODE
;+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
ORG 0F000h ; program start for MSP430F122
;___________________________
; Reset Interrupt sequence
;___________________________
RESET
MOV.W #0300h, SP ; initialize stack pointer
CALL #INIT ; initalize the UART

MAIN
BIS #LPM4+GIE, SR ; wait for start-edge
NOP ; Needed by debugger
CMP.B #f0, r8 ; check received data
JNZ MAIN ; incorrect data! jmp!
XOR.B #1, P1OUT ; toggle LED pin to ack received flag
JMP MAIN

;_______________________________________________________________________
; USART Interrupt sequence
;_______________________________________________________________________
RECEIVE
BIT.B #URXIFG0,&IFG2 ; Test URXIFGx to determine
JNZ StartRec ; If start-edge or character
; if IFG is set, Z=0, continue.
; if IFG not set (no complete
transmission), return!

StartEdge ; wake up and receive char
BIC.B #URXSE,&U0TCTL ; Clear URXS signal
BIS.B #URXSE,&U0TCTL ; Re-enable edge detect
BIC #SCG0+SCG1,0(SP) ; Enable BRCLK = DCO; CPU still off
JMP EndRcv

StartRec
MOV.B &U0RXBUF, r8 ; Save received char in r8
BIC #OE+FE+PE+RXERR,U0RCTL ;Clear any errors received
BIC #LPM4+GIE,0(SP) ; Char received, wake up and process
data

EndRcv
RETI

;_______________________________________________________________________
; Initialization function (sets up UART, flags and interrupts)
;_______________________________________________________________________
INIT
MOV.W #WDTPW+WDTHOLD, &WDTCTL ; stop watchdog
BIS #OSCOFF, SR ; not using LFXTL1

//Initialize UART
BIS.B #CHAR, &U0CTL
; 1 stop bit
; 8-bit word
BIS.B #SSEL1, &U0TCTL ; use sub-main clock for UART (@750kHz)
MOV.B #RATIO, &U0BR0 ; f = 750kHz in MSP430F122
MOV.B #000h, &U0BR1 ;
MOV.B #00h, &U0MCTL ; receive moodulation set to zero; 0.05
is small
BIS.B #URXSE, &U0TCTL ; enable start-edge wake-up
BIS.B #020h, &P3SEL ; select P3.5 for serial reception
BIC.B #020h, &P3DIR ; and input
BIS.B #URXE0, &ME2 ; enable receiver (MSP430F122)
BIC.B #SWRST, &U0CTL ; clear UART software reset
BIS.B #URXIE0, &IE2 ; enable receiver interrupt
(MSP430F122)

BIS.B #003h, &P1DIR ; P1.1 and P1.0 output
BIS.B #003h, &P1OUT ; turn LEDs off

EINT ; enable interrupts: GIE<-1

RET

END

Mark Borgerson

Mark is right. Been there, done that.

When you sleep in LPM4, there is only one way to get out of it: you can
use an interrupt from any peripheral that *doesn't* use a clock. All
clocks are off in LPM4.

Waking from LPM4 is slow because it takes some time for the clocks to
restart. If you're app demands single clock cycle response on wakeup,
then LPM3 might be a better choice for sleeping.

They call LMP4 "done mode". Please take that tag literally. You're
app woll be done doing whatever it's doing if it's in LPM4. LPM is
called "sleep mode". Your app will be active but waiting to wakeup
(IOW, not done).

There is a useful table in the User' Guide that shows which clocks are
on and off for the various LPMs.

JJS

IIRC, the LPM4 mode shuts off all the clocks, including that to the
UART. Are you sure that the UART clock is starting up quickly
enough
to capture the start bit?

If the data is really received in a constant stream, you might be
better off not going into LPM4 mode after each character---but
only when no character has been received for a pre-determined
interval.

jerry_bp wrote:

Hi all, I'm currently working in an application that requires the MCU to go
into deep sleep (LPM4) and wake up and process data on UART receive, and
then go back to LPM4. What is the right way to do this? I tried doing the
following as TI's guide Rev. E. suggests, but this crashes the MCU. I
tried to debug the code but I just can't find where the problem is. The
serial data is received using IR, in a constant stream that does not stop
until the "transmitter" is taken away from the receiver. This will work
fine for a while but it eventually crashes.

Just some thoughts:
- Does your code work properly while not going LPM or going to another LPM?

What I've seen is that somehow when the software is busy handling an
interrupt, it STILL accepts other interrupts even when the GIE bit is off.

- You turn it on inside the interrupt routine. Don't do it, the CPU will
turn it on while executing RETI.

Sometimes the instruction that sends the MCU back to active mode doesn't do
anything or messes everything up. I really need help here as I'm running
out of ideas. BTW, the problem is not on hardware, all of the required
pins are correctly terminated to either VCC or ground, even the
programming pins, reset, etc.

You don't properly switch the CPU to inactive mode - you don't use
CPUOFF bit.

MAIN
BIS #LPM4+GIE, SR ; wait for start-edge

GIE is already 1 before this instruction.

NOP ; Needed by debugger
Needed only if there is nothing after it - it's not your case.

CMP.B #f0, r8 ; check received data
JNZ MAIN ; incorrect data! jmp!
XOR.B #1, P1OUT ; toggle LED pin to ack received flag
JMP MAIN
BIC #OE+FE+PE+RXERR,U0RCTL ;Clear any errors received
BIC #LPM4+GIE,0(SP) ; Char received, wake up and process
data

Why do you turn interrupts off here?

BIS.B #020h, &P3SEL ; select P3.5 for serial reception
BIC.B #020h, &P3DIR ; and input

Actually it's an output here.