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List:       openocd-development
Subject:    [Openocd-development] Algorithm parameters
From:       Dominic.Rath () gmx ! de (Dominic Rath)
Date:       2006-11-07 12:16:11
Message-ID: 200611071316.11525.Dominic.Rath () gmx ! de
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Hello Magnus,

I see what you mean. The idea was to keep this consistent with the rest of the 
OpenOCD, especially with the JTAG subsystem. There, out_value etc. mean data 
output to the device, while in_value is the data being read back to the host.

I agree that the naming convention used by RPC for example might be more 
appropriate, but I'm not sure if this is important enough to justify a 
change.

An algorithm must not expect the state to be kept between several invocations. 
It can't know if another algorithm ran in between, like the LPC code that 
calls target_write_buffer, which might use the DCC. The host code can use 
PARAM_IN_OUT if it wants to reuse a register value.
I'll change the init_reg_param code to initialize PARAM_IN to -1, instead of 
the current indeterminate state. That should allow potential bugs to be 
spotted more easily.

Regards,

Dominic

On Wednesday 25 October 2006 22:36, Magnus Lundin wrote:
> Hello
>
> Maybe this is just me being extremely sensitive but:
>
> Parameters are of three kinds:
>     PARAM_IN,
>     PARAM_OUT,
>     PARAM_IN_OUT
>
> Thats good, but is this with respect to the algorithm or the calling
> program.
> The parameters are specified using the internal registers used in the
> algoritm "r0" , etc
> so they are defined from the point of view of the algorithm. Thus
> PARAM_IN goes
>
> >from the caller into the algorithm. It is an input to "r0"
>
> This is more in line with the usage when defining remote procedure call
> parameters in
> most situations I have seen. Corba,  Com .
>
> The current usage is not wrong or illogical but for me it feels strange
> and nonstandard.
>
> Anyway, in the armv4_5 implementation when setting up the call, the
> IN/OUT status (however we interpret it)
> should be respected so we do not write values to memory or reigsters
> unless it is an input to
> the  algortim. This might be  important when setting up an algorithm and
> the running it  several
> times keeping the intermediate state. Not very likely but it might happen.
>
>
> Just my gut feelings.
>
> Regards,
>
> Magnus
>
>
>
>
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