Re: Brainstorming on recursive class definitions

[moogyd--- via Python-list]

On Tuesday, September 12, 2017 at 5:37:31 PM UTC+2, Johannes Bauer wrote:
> Hi group,
> 
> so I'm having a problem that I'd like to solve *nicely*. I know plenty
> of ways to solve it, but am curious if there's a solution that allows me
> to write the solution in a way that is most comfortable for the user.
> 
> I'm trying to map registers of a processor. So assume you have a n bit
> address space, the processor might have duplicate units of identical
> functionality mapped at different places in memory. For example, assume
> there's a GPIO unit that has registers FOO, BAR and KOO and two GPIO
> ports GPIOA and GPIOB. I'd like to write code along the lines of this:
> 
> class GpioMap(BaseRegisterMap):
>   FOO = 0x0
>   BAR = 0x4
>   KOO = 0x8
> 
> class CPURegisterMap(BaseRegisterMap):
>   GPIOA = GpioMap(0x1)
>   GPIOB = GpioMap(0x2)
> 
> cpu = CPURegisterMap(0x8000)
> 
> assert(cpu.addr == 0x8000)
> assert(cpu.GPIOA.addr == 0x8000 + 0x1)
> assert(cpu.GPIOB.addr == 0x8000 + 0x2)
> assert(cpu.GPIOA.FOO.addr == 0x8000 + 0x1 + 0x0)
> assert(cpu.GPIOA.KOO.addr == 0x8000 + 0x1 + 0x8)
> assert(cpu.GPIOB.BAR.addr == 0x8000 + 0x2 + 0x4)
> 
> So, obviously, FOO, BAR and KOO are of type "int" without any "addr"
> property, so there would need to be some magic there. Additionally,
> through some way the instanciation of GpioMap() would need the knowledge
> of its parent base, which I'm not sure is even possible. Maybe (that's
> what I'm currently trying to get right) the __getattribute__ would
> propagate the information about the accumulated parent's base address to
> the child during lookup.
> 
> Anyways, I'm looking for your ideas on how to solve such a thing
> "nicely". Note that "BaseRegisterMap" is allowed to do dirty things as
> long as the definition code has a clean look & feel.
> 
> Cheers,
> Joe
> 
> 
> -- 
> >> Wo hattest Du das Beben nochmal GENAU vorhergesagt?
> > Zumindest nicht öffentlich!
> Ah, der neueste und bis heute genialste Streich unsere großen
> Kosmologen: Die Geheim-Vorhersage.
>  - Karl Kaos über Rüdiger Thomas in dsa 

A child (e.g. instance of GpioMap) should not have any knowledge of it's own 
base address. This is a function of the GPIORegisyerMap only.
i.e. The GPIORegisyerMap  would do the selection of particular instance.

It may be worth looking at some of the IP-XACT documentation, which defines 
some common terms (IIRC register, address map, address space etc). Having a 
consistent definition here will definitely help moving forward
Although it may seem OTT at the moment, it is something you should consider at 
the outset.
e.g. A single GPIO register may occur at two different addresses, depending on 
the bus master (CPU Core, Debugger, External SPI access).

Steven

-- 
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Brainstorming on recursive class definitions

[Johannes Bauer]

Hi group,

so I'm having a problem that I'd like to solve *nicely*. I know plenty
of ways to solve it, but am curious if there's a solution that allows me
to write the solution in a way that is most comfortable for the user.

I'm trying to map registers of a processor. So assume you have a n bit
address space, the processor might have duplicate units of identical
functionality mapped at different places in memory. For example, assume
there's a GPIO unit that has registers FOO, BAR and KOO and two GPIO
ports GPIOA and GPIOB. I'd like to write code along the lines of this:

class GpioMap(BaseRegisterMap):
FOO = 0x0
BAR = 0x4
KOO = 0x8

class CPURegisterMap(BaseRegisterMap):
GPIOA = GpioMap(0x1)
GPIOB = GpioMap(0x2)

cpu = CPURegisterMap(0x8000)

assert(cpu.addr == 0x8000)
assert(cpu.GPIOA.addr == 0x8000 + 0x1)
assert(cpu.GPIOB.addr == 0x8000 + 0x2)
assert(cpu.GPIOA.FOO.addr == 0x8000 + 0x1 + 0x0)
assert(cpu.GPIOA.KOO.addr == 0x8000 + 0x1 + 0x8)
assert(cpu.GPIOB.BAR.addr == 0x8000 + 0x2 + 0x4)

So, obviously, FOO, BAR and KOO are of type "int" without any "addr"
property, so there would need to be some magic there. Additionally,
through some way the instanciation of GpioMap() would need the knowledge
of its parent base, which I'm not sure is even possible. Maybe (that's
what I'm currently trying to get right) the __getattribute__ would
propagate the information about the accumulated parent's base address to
the child during lookup.

Anyways, I'm looking for your ideas on how to solve such a thing
"nicely". Note that "BaseRegisterMap" is allowed to do dirty things as
long as the definition code has a clean look & feel.

Cheers,
Joe


-- 
>> Wo hattest Du das Beben nochmal GENAU vorhergesagt?
> Zumindest nicht öffentlich!
Ah, der neueste und bis heute genialste Streich unsere großen
Kosmologen: Die Geheim-Vorhersage.
 - Karl Kaos über Rüdiger Thomas in dsa 
-- 
https://mail.python.org/mailman/listinfo/python-list