[Qemu-devel] Fw: Max7310: confused about the method of reading output port register

[Qemu-devel] Fw: Max7310: confused about the method of reading output port register

[Yang Ning]

Dear  All:

Firstly,I'm writing to express my thanks to Zaborowski for the source 
code of Max7310 which have helped me so much.
  But I'm still confused about the method of reading output port register.
code:
>    case 0x01:	/* Output port */
>        return s->level & ~s->direction;
>        break;

I found some instruction of output port register in the datasheet.
>" Reads from the output port register reflect the value that is in the flip-flop
>controlling the output selection, not the actual I/O value, which may differ if
>the out-put is overloaded."

So,in my opinion,in the defination of MAX7310State,whether the property 
of outputport_reg should be added?
And does the method of reading/writing output port should be modified as 
follows.

[reading]
     case 0x01:	/* Output port */
         return s->outputport_reg;
         break;
[writing]
     case 0x01:	/* Output port */
>        for (diff = (data ^ s->level) & ~s->direction; diff;
>                        diff &= ~(1 << line)) {
>           line = ffs(diff) - 1;
>            if (s->handler[line])
>                qemu_set_irq(s->handler[line], (data >> line) & 1);
>        }
>        s->level = (s->level & s->direction) | (data & ~s->direction);
         s->outputport_reg =  data;
         break;	

Re: [Qemu-devel] Fw: Max7310: confused about the method of reading output port register

[andrzej zaborowski]

Hi Yang,

On 26 August 2013 03:47, Yang Ning <yangn.fnst@cn.fujitsu.com> wrote:
>
> Dear  All:
>
> Firstly,I'm writing to express my thanks to Zaborowski for the source code
> of Max7310 which have helped me so much.
>  But I'm still confused about the method of reading output port register.
> code:
>>
>>    case 0x01:   /* Output port */
>>        return s->level & ~s->direction;
>>        break;
>
>
> I found some instruction of output port register in the datasheet.
>>
>> " Reads from the output port register reflect the value that is in the
>> flip-flop
>> controlling the output selection, not the actual I/O value, which may
>> differ if
>> the out-put is overloaded."
>
>
> So,in my opinion,in the defination of MAX7310State,whether the property of
> outputport_reg should be added?
> And does the method of reading/writing output port should be modified as
> follows.
>
> [reading]
>     case 0x01:  /* Output port */
>         return s->outputport_reg;
>         break;
> [writing]
>     case 0x01:  /* Output port */
>>
>>        for (diff = (data ^ s->level) & ~s->direction; diff;
>>                        diff &= ~(1 << line)) {
>>           line = ffs(diff) - 1;
>>            if (s->handler[line])
>>                qemu_set_irq(s->handler[line], (data >> line) & 1);
>>        }
>>        s->level = (s->level & s->direction) | (data & ~s->direction);
>
>         s->outputport_reg =  data;
>         break;

Yes, if by "overload" they mean change direction to "input", then yes,
I think you are correct.

Personally I'd call it s->output.  I'm wondering if we may need to
update the output levels when the Configuration (0x03) is written and
on reset.  This would be best done by adding a short function
max7310_update() that does the "for (diff = ...)" loop and calls
qemu_set_irq.

Best regards