Lpc2000

Hi. What would be the software sequence the most similar to a 
hardware reset? I am aware that certain things cannot be changed from 
software, like the watchdog, once it is started, but perhaps there's 
something closer to a reset than:

msr   CPSR_c,#MODE_SVC|I_BIT|F_BIT
b 0

This would not work if in user mode, for instance, for I cannot 
change CPSR from that mode, I guess.

I am using LPC2138/LPC2148 in my board. Perhaps the IAP/ISP code 
could be useful somehow?

I've been thinking on reusing an existing exception to start 
such "software reset", like Undefined or something, but I rather use 
it to detect the true exception if I can manage. I would like to 
write a solid piece of software, so I want all the bases covered, 
whenever possible.

Any ideas?

Guille

Guillermo,

From past experience, the best way to "soft" reset a microcontroller 
is to use some form of hardware reset. I haven't heard of any issues 
with any of the LPC2000 series peripherals, but on some micros, it is 
possible for some of the peripherals to get latched into states that 
can't be recoevered by software (that is, you can't reliably re-
configure them). Because of this, some form of hardware reset is 
usually best to get the system into a known, initial, state.

Two suggestions:

1. If you can spare an I/O pin, use an o/p pin to feed-back into the 
reset line (i.e. self-reset). Advantage: simple. Disadvantage: need 
h/w.

2. Use the watchdog: configure it for a very short time, and then 
spin round (or goto idle state) without feeding it. Advantage: 
reasonably simple, no hardware required. Disadvantage: you may 
already be using the watchdog, and if so, may need additional code to 
distinguish a real watchdog (unexpected) reset from an intended soft 
reset.

I'm sure there's plenty of other ways too.

Brendan

--- In lpc2000@yahoogroups.com, "Guillermo Prandi" 
<yahoo.messenger@m...> wrote:
>
> Hi. What would be the software sequence the most similar to a 
> hardware reset? I am aware that certain things cannot be changed 
from 
> software, like the watchdog, once it is started, but perhaps 
there's 
> something closer to a reset than:
> 
> msr   CPSR_c,#MODE_SVC|I_BIT|F_BIT
> b 0
> 
> This would not work if in user mode, for instance, for I cannot 
> change CPSR from that mode, I guess.
> 
> I am using LPC2138/LPC2148 in my board. Perhaps the IAP/ISP code 
> could be useful somehow?
> 
> I've been thinking on reusing an existing exception to start 
> such "software reset", like Undefined or something, but I rather 
use 

> it to detect the true exception if I can manage. I would like to 
> write a solid piece of software, so I want all the bases covered, 
> whenever possible.
> 
> Any ideas?
> 
> Guille
>

Thanks, Brendan. Yes, I thought of a hardware reset, but modifying 
the board is no longer an option at this stage. However, I would like 
to -by software- do my best effort to handle this, although I know I 
can't really cover all bases.

About the watchdog, I am concerned about such a short timer. Since 
there is no way I can turn the watchdog off by software, couldn't my 
reset procedure be continually called by the watchdog, with not 
enough time to reset it properly? The LPC2138 user manual doesn't say 
if the watchdog is stopped after triggered (or at least I couldn't 
find a word about it). In fact, once the watchdog is set up, what 
attributes am I allowed to change from it afterwards?

Another way that just occurred to me is the following:

1) Disable all interrupts
2) Relocate the interrupt vectors into RAM (I was using ROM vectors)
3) Place a dummy SWI at the SWI vector
4) Produce a SWI
5) Inside the SWI handler (now in supervisor mode!),
relocate the interrupt vectors into ROM again and perform "b 0".

Too messy for my liking, but it is the only sure way to enter 
supervisor mode from user mode without wasting an exception mode. 
(Currently SWI is being used by the FreeRTOS port to perform a Yield).

Guille

--- In lpc2000@yahoogroups.com, "brendanmurphy37" 
<brendan.murphy@i...> wrote:
>
> 
> Guillermo,
> 
> From past experience, the best way to "soft" reset a 
microcontroller 
> is to use some form of hardware reset. I haven't heard of any 
issues 
> with any of the LPC2000 series peripherals, but on some micros, it 
is 
> possible for some of the peripherals to get latched into states 
that 
> can't be recoevered by software (that is, you can't reliably re-
> configure them). Because of this, some form of hardware reset is 
> usually best to get the system into a known, initial, state.
> 
> Two suggestions:
> 
> 1. If you can spare an I/O pin, use an o/p pin to feed-back into 
the 
> reset line (i.e. self-reset). Advantage: simple. Disadvantage: need 
> h/w.
> 
> 2. Use the watchdog: configure it for a very short time, and then 
> spin round (or goto idle state) without feeding it. Advantage: 
> reasonably simple, no hardware required. Disadvantage: you may 
> already be using the watchdog, and if so, may need additional code 
to 
> distinguish a real watchdog (unexpected) reset from an intended 
soft 

> reset.
> 
> I'm sure there's plenty of other ways too.
> 
> Brendan
> 
> --- In lpc2000@yahoogroups.com, "Guillermo Prandi" 
> <yahoo.messenger@m...> wrote:
> >
> > Hi. What would be the software sequence the most similar to a 
> > hardware reset? I am aware that certain things cannot be changed 
> from 
> > software, like the watchdog, once it is started, but perhaps 
> there's 
> > something closer to a reset than:
> > 
> > msr   CPSR_c,#MODE_SVC|I_BIT|F_BIT
> > b 0
> > 
> > This would not work if in user mode, for instance, for I cannot 
> > change CPSR from that mode, I guess.
> > 
> > I am using LPC2138/LPC2148 in my board. Perhaps the IAP/ISP code 
> > could be useful somehow?
> > 
> > I've been thinking on reusing an existing exception to start 
> > such "software reset", like Undefined or something, but I rather 
> use 
> > it to detect the true exception if I can manage. I would like to 
> > write a solid piece of software, so I want all the bases covered, 
> > whenever possible.
> > 
> > Any ideas?
> > 
> > Guille
> >
>

I still think the best way is to create a reset routine that will reset the
processor using the watchdog timer, as someoe else mentioned.  I've
encountered this issue many times over years, and using the watchdog was
always the best way.
I'm rather sure that once the processor is reset, you have to re-enable it
for your application (as you do normally on powerup).  It shouldn't stay
enabled across reset.

--
Jim Parziale
nuncio.bitis@...
Malden, MA


On 1/30/06, Guillermo Prandi <yahoo.messenger@...> wrote:
>
>  Thanks, Brendan. Yes, I thought of a hardware reset, but modifying
> the board is no longer an option at this stage. However, I would like
> to -by software- do my best effort to handle this, although I know I
> can't really cover all bases.
>
> About the watchdog, I am concerned about such a short timer. Since
> there is no way I can turn the watchdog off by software, couldn't my
> reset procedure be continually called by the watchdog, with not
> enough time to reset it properly? The LPC2138 user manual doesn't say
> if the watchdog is stopped after triggered (or at least I couldn't
> find a word about it). In fact, once the watchdog is set up, what
> attributes am I allowed to change from it afterwards?
>
> Another way that just occurred to me is the following:
>
> 1) Disable all interrupts
> 2) Relocate the interrupt vectors into RAM (I was using ROM vectors)
> 3) Place a dummy SWI at the SWI vector
> 4) Produce a SWI
> 5) Inside the SWI handler (now in supervisor mode!),
> relocate the interrupt vectors into ROM again and perform "b 0".
>
> Too messy for my liking, but it is the only sure way to enter
> supervisor mode from user mode without wasting an exception mode.
> (Currently SWI is being used by the FreeRTOS port to perform a Yield).
>
> Guille
>
> --- In lpc2000@yahoogroups.com, "brendanmurphy37"
> <brendan.murphy@i...> wrote:
> >
> >
> > Guillermo,
> >
> > From past experience, the best way to "soft" reset a
> microcontroller
> > is to use some form of hardware reset. I haven't heard of any
> issues
> > with any of the LPC2000 series peripherals, but on some micros, it
> is
> > possible for some of the peripherals to get latched into states
> that
> > can't be recoevered by software (that is, you can't reliably re-
> > configure them). Because of this, some form of hardware reset is
> > usually best to get the system into a known, initial, state.
> >
> > Two suggestions:
> >
> > 1. If you can spare an I/O pin, use an o/p pin to feed-back into
> the
> > reset line (i.e. self-reset). Advantage: simple. Disadvantage: need
> > h/w.
> >
> > 2. Use the watchdog: configure it for a very short time, and then
> > spin round (or goto idle state) without feeding it. Advantage:
> > reasonably simple, no hardware required. Disadvantage: you may
> > already be using the watchdog, and if so, may need additional code
> to
> > distinguish a real watchdog (unexpected) reset from an intended
> soft
> > reset.
> >
> > I'm sure there's plenty of other ways too.
> >
> > Brendan
> >
> > --- In lpc2000@yahoogroups.com, "Guillermo Prandi"
> > <yahoo.messenger@m...> wrote:
> > >
> > > Hi. What would be the software sequence the most similar to a
> > > hardware reset? I am aware that certain things cannot be changed
> > from
> > > software, like the watchdog, once it is started, but perhaps
> > there's
> > > something closer to a reset than:
> > >
> > > msr   CPSR_c,#MODE_SVC|I_BIT|F_BIT
> > > b 0
> > >
> > > This would not work if in user mode, for instance, for I cannot
> > > change CPSR from that mode, I guess.
> > >
> > > I am using LPC2138/LPC2148 in my board. Perhaps the IAP/ISP code
> > > could be useful somehow?
> > >
> > > I've been thinking on reusing an existing exception to start
> > > such "software reset", like Undefined or something, but I rather
> > use
> > > it to detect the true exception if I can manage. I would like to
> > > write a solid piece of software, so I want all the bases covered,
> > > whenever possible.
> > >
> > > Any ideas?
> > >
> > > Guille
> > >
> >
>
>


[Non-text portions of this message have been removed]

Hi,

The watchdog, if it underflows, does a reset of the system. According 
to the manual (I'm looking at the LPC213x User Manual), and I see no 
reason to doubt it, there's very few differences between an internal 
(watchdog) reset and an external (reset pin) reset.

The watchdog mode register description in tne same manual shows that 
the reset value of the enabled flags is 0 (i.e. not enabled). I'd 
take that to mean that there's no danger of what you're concerned 
about (i.e. an infinite loop of watchdog resets).

Bottom line: if you trust the manual contents, it should be OK for 
your purposes (indeed, I hope that it is, as it's exactly what we do 
for a "soft" reset). As you point out, attempting to do it in 
software can get messy very fast, if you want something general 
purpose.

Regards
Brendan

--- In lpc2000@yahoogroups.com, "Guillermo Prandi" 
<yahoo.messenger@m...> wrote:
>
> Thanks, Brendan. Yes, I thought of a hardware reset, but modifying 
> the board is no longer an option at this stage. However, I would 
like 
> to -by software- do my best effort to handle this, although I know 
I 
> can't really cover all bases.
> 
> About the watchdog, I am concerned about such a short timer. Since 
> there is no way I can turn the watchdog off by software, couldn't 
my 
> reset procedure be continually called by the watchdog, with not 
> enough time to reset it properly? The LPC2138 user manual doesn't 
say 

> if the watchdog is stopped after triggered (or at least I couldn't 
> find a word about it). In fact, once the watchdog is set up, what 
> attributes am I allowed to change from it afterwards?
>

You are right, Brendan, Jim. I just tested and the watchdog, once 
triggered, won't trigger again until it is set up again. So I will 
use the watchdog with a pretty short timer (minimum = 0xff) and then 
enter an endless "enter idle mode" loop. It looks like interrupts can 
take you out of idle mode even if they are disabled.

Thank you all.

Guille

--- In lpc2000@yahoogroups.com, "brendanmurphy37" 
<brendan.murphy@i...> wrote:
>
> 
> Hi,
> 
> The watchdog, if it underflows, does a reset of the system. 
According 
> to the manual (I'm looking at the LPC213x User Manual), and I see 
no 
> reason to doubt it, there's very few differences between an 
internal 
> (watchdog) reset and an external (reset pin) reset.
> 
> The watchdog mode register description in tne same manual shows 
that 
> the reset value of the enabled flags is 0 (i.e. not enabled). I'd 
> take that to mean that there's no danger of what you're concerned 
> about (i.e. an infinite loop of watchdog resets).
> 
> Bottom line: if you trust the manual contents, it should be OK for 
> your purposes (indeed, I hope that it is, as it's exactly what we 
do 
> for a "soft" reset). As you point out, attempting to do it in 
> software can get messy very fast, if you want something general 
> purpose.
> 
> Regards
> Brendan
> 
> --- In lpc2000@yahoogroups.com, "Guillermo Prandi" 
> <yahoo.messenger@m...> wrote:
> >
> > Thanks, Brendan. Yes, I thought of a hardware reset, but 
modifying 
> > the board is no longer an option at this stage. However, I would 
> like 
> > to -by software- do my best effort to handle this, although I 
know 
> I 
> > can't really cover all bases.
> > 
> > About the watchdog, I am concerned about such a short timer. 
Since 
> > there is no way I can turn the watchdog off by software, couldn't 
> my 
> > reset procedure be continually called by the watchdog, with not 
> > enough time to reset it properly? The LPC2138 user manual doesn't 
> say 
> > if the watchdog is stopped after triggered (or at least I 
couldn't 

> > find a word about it). In fact, once the watchdog is set up, what 
> > attributes am I allowed to change from it afterwards?
> >
>