Re: [Qemu-devel] [PATCH] armv7-m: exit on external reset request

[Michael Davidsaver]

On 10/09/2015 02:18 PM, Peter Crosthwaite wrote:
> On Fri, Oct 9, 2015 at 10:25 AM, Michael Davidsaver
> <address@hidden> wrote:
>>
>>
>> On 10/09/2015 12:59 PM, Peter Maydell wrote:
>>> On 8 October 2015 at 16:40, Michael Davidsaver <address@hidden> wrote:
>>>> ...
>>>>      case 0xd0c: /* Application Interrupt/Reset Control.  */
>>>>          if ((value >> 16) == 0x05fa) {
>>>> +            if (value & 4) {
>>>> +                qemu_system_reset_request();
>>>> +            }
>> ...
>>>
>>> Strictly speaking what this bit does is assert a signal out of
>>> the CPU to some external power management or similar device
>>> in the SoC, which then is responsible for doing the reset.
>>> So just calling qemu_system_reset_request() here is a bit of
>>> a shortcut. But maybe it's a pragmatic shortcut?
>>
>> I'm not sure what you mean by shortcut?  Most targets have some way to 
>> trigger qemu to exit.  I actually compiled a list recently (see below).  I 
>> couldn't find one for the lm3s6965evb machine, thus this patch.
>>
> 
...
> I think it would be better for SoC (or board) level to
> install the GPIO handler to do the reset. As far as target-arm is
> concerned this is then just a GPIO.

I don't think I'm well versed enough in qemu lingo to parse this sentence :)
Are you concerned about adding this function to AIRCR (which would effect every 
armv7-m board),
or about directly calling qemu_system_reset_request() in armv7m_nvic.c?


> We should check the lm3s docs to see what the implementation of this
> signal is.

To quote page 129 of http://www.ti.com/lit/ds/symlink/lm3s6965.pdf

> System Reset Request
> Value Description
> 0
>  No effect.
> 1
>  Resets the core and all on-chip peripherals except the Debug
> interface.
> This bit is automatically cleared during the reset of the core and reads
> as 0.

There is also mention of a board specific watchdog timer.

I also looked at the TI MSP432P4xx (I have one), which give a similar 
definition for this bit (along with a dozen board specific ways to do different 
reset levels...)