On 17.11.2015 15:12, Jan Kandziora wrote:
>
>> >
>> > NB: while we're looking at the DS2409 code ... OWCH:
>> >
>> > /* 2409 switch -- branch status -- note that bit value is reversed */
>> > static ZERO_OR_ERROR FS_r_branch(struct one_wire_query *owq)
>> > {
>> > BYTE data = 0 ;
>> >
>> > OWQ_U(owq) = (((data) & 0x01) | ((data >> 1) & 0x02)) ^ 0x03;
>> > return GB_to_Z_OR_E(OW_r_control(&data, PN(owq))) ;
>> > }
>> >
>> > Wouldn't it make slightly more sense to *first* read data and *then* set
>> > the return value? :-P
>> >
> Wait, wait. What do you object here exactly?
>
>
I admit that I had problems with this code myself. However …
* set data to zero
* set output value to 3 ('data' is zero)
* read 'data' from bus
* … but don't use it in any way.
Disassembly of the code demonstrates that the value 3 is set.
(I admit that I double-checked despite the evidence.)
0000000000000140 <FS_r_branch>:
140: 48 83 ec 18 sub $0x18,%rsp
144: 48 8d 77 18 lea 0x18(%rdi),%rsi
148: c7 87 b0 30 00 00 03 movl $0x3,0x30b0(%rdi)
--
-- Matthias Urlichs
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