SCPI-99:9.4 Implement "fan-out" register support

[sandsbl]

As part of our SCPI instrument development, we have come upon a need to include "fan-out" registers for certain bits in QUEStionable and OPERation status registers as defined in section 9.4 of the SCPI-99 spec. I propose adding this as a feature-request for the scpi-parser library. I am willing to work on this feature, as we are in the most immediate need for it, but I would like to get some feedback on my thoughts on how to proceed. I am thinking to take the following steps to implement this feature:

• Add the member scpi_fanout_reg_t * fanout_registers; to _scpi_t context structure
  This would be a pointer to an array of device-specific fanout registers that would need to be defined in scpi_context.c. Each fanout register could be defined in types.h as

  struct  _scpi_fanout_reg_t {
  scpi_reg_val_t val;
  scpi_reg_name_t parent_reg;
  scpi_reg_val_t parent_bit;
  int32_t parent_fanout_reg;
  scpi_bool_t is_nested;
  };
  typedef struct _scpi_fanout_reg_t scpi_fanout_reg_t;
  

  This specifies the register value val, its standard parent register parent_reg (one of OPER or QUES), and the summary bit to which this fanout is logically summed parent_bit. Since the standard specifies the potential for multiple layers of nesting fanout registers, the last two members would handle this case. If is_nested is TRUE, then the fanout register at index parent_fanout_reg is updated as a summary bit.

• Extend SCPI_RegXXX functions in IEEE488.c
  The following functions would need to have their "fanout" analogs added to handle scpi_fanout_reg_t registers:
  SCPI_RegSet -> SCPI_RegSetFanout SCPI_RegSetBits -> SCPI_RegSetFanoutBits SCPI_RegClearBits -> SCPI_RegClearFanoutBits SCPI_RegGetFanout -> SCPI_RegGetFanout regUpdate -> regUpdateFromFanout
  Additionally, there is a need for a new function SCPI_RegCheckBits that would check if a particular register bit from OPER or QUES is a summary bit. This would presumably be used e.g. when a *CLS command is issued or when a summary bit is read in order to clear its associated fanout registers.

• Update SCPI_CoreCLS in IEEE488.c
  Clear fanout registers.

• Update QUEStionable and OPERation status callbacks as well as SCPI_StatusPreset in minimal.c
  Handle fanout registers.

Please advise with suggestions or issues I may have forgot.

[j123b567]

I thing, there was no discussion about this in the past.

Can you propose a pull request with this functionality?

[sandsbl]

Yes, I can start working on it.

[PolyPik]

@sandsbl Have you implemented this feature?

[sandsbl]

No, I haven't had a chance to, sorry. Moved to another project.

On Wed, Apr 15, 2020 at 5:51 PM PolyPik [email protected] wrote:

@sandsbl https://github.com/sandsbl Have you implemented this feature?

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[PolyPik]

Well you did a pretty good job of describing what needs to be done. I think I can implement the changes on my own.

[j123b567]

Should be fixed by #114

[jancumps]

@PolyPik , do you happen to have an example or test case that uses device specific registers? I'm trying to use the functionality, to flag that a digital input has changed level. I am investigating how to use the extension by trying to use it in my project. An example or reference project would be helpful.

[jancumps]

I figured it out. I managed to build a set of instrument specific registers,
make them fan out to a bit of the OPERATION STATUS register, etc...
Took me a good week to fully make it happen :) - partly because I wanted a good integration with TinyUSB's TMCUSB with service requests.

documentation link.