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//! FSM egress.
use super::*;
impl<P: Copy, R: Copy, const D: Dep> I<VrH<P, R>, D> {
/// For each transferred ingress payload, runs a finite state machine described by `f` until `f` returns true for
/// `is_last`.
///
/// This allows you to process each ingress payload using multiple FSM states.
///
/// - Payload: Controlled by the combinator's behavior.
/// - Resolver: The ingress ready signal is controlled by the combinator's behavior. The inner value `R` of the
/// resolver is preserved.
///
/// | Interface | Ingress | Egress |
/// | :-------: | ------------ | ------------- |
/// | **Fwd** | `HOption<P>` | `HOption<EP>` |
/// | **Bwd** | `Ready<R>` | `Ready<R>` |
///
/// # Detailed explanation
///
/// ## Parameters
///
/// - `init`: The initial state for the FSM.
/// - `pipe`: If true, starts a new FSM immediately after an FSM finishes if an input is available. If false,
/// transitions to a waiting case first then accept an input for a new FSM.
/// - `flow`: If true, starts running the FSM immediately from the cycle of an ingress transfer. If false, starts
/// running the FSM from the next cycle of an ingress transfer.
/// - `f`: The function that describes the FSM. If `let (ep, s_next, is_last) = f(p, s)`,
/// - `p`: The current saved ingress payload for this FSM.
/// - `s`: The current FSM state.
/// - `ep`: The calculated egress payload.
/// - `s_next`: The next FSM state.
/// - `is_last`: Whether this is the last state of the FSM for the current saved payload.
///
/// The `pipe` and `flow` parameters are inspired by
/// <https://github.com/chipsalliance/chisel/blob/9c1829e6afe8a08630c90d5a0f30bce9c487075f/src/main/scala/chisel3/util/Decoupled.scala#L243>.
///
/// ## High-level overview of the behavior
///
/// The combinator can be in one of the two cases: **Waiting for an ingress transfer** and **Running the FSM**.
///
/// Initially, the combinator is in the **Waiting for an ingress transfer** case and waits for an ingress transfer
/// to happen. Once an ingress transfer happens, it saves the ingress payload to transition to the **Running the
/// FSM** case, and starts a new FSM. Whether this happens on the same cycle as the transfer or on the next cycle
/// depends on `flow`.
///
/// In the **Running the FSM** case, the combinator runs the FSM with the saved payload outputting egress payloads.
/// When `f` returns true for `is_last`, it will save a new ingress payload and start a new FSM, if `pipe` is true
/// and the new ingress payload is already available. Otherwise, it will transition back to the **Waiting for an
/// ingress transfer** case next cycle.
///
/// ## Detailed behavior
///
/// > NOTE: The description below assumes the following naming convention. Here, `sp` is the saved ingress payload
/// > and determines the case the combinator is in. `s` is the FSM state. The description is organized sligtly
/// > differently from the actual implementation for better clarity.
/// >
/// > ```ignore
/// > // an implementation of `fsm_egress`
/// > self.fsm((None, init), |ip, er, (sp, s)| {
/// > // ... the description below would fit here
/// > (ep, ir, (sp_next, s_next))
/// > })
/// > ```
///
/// - **Waiting for an ingress transfer** (`sp == None`)
/// - Do not produce an egress payload: `ep = None`
/// - Can accept a new ingress payload: `ir = (true, er.inner)`
/// - If an ingress transfer happens (`if it`),
/// - If `flow`,
/// - (The description below is not how the actual code works, but conceptually the behavior should be
/// the same.)
/// - Conceptually save the ingress payload and transition to the **Running the FSM** case *this* cycle:
/// `sp = ip`
/// - Start a new FSM with the initial state *this* cycle: `s = init`
/// - Run the logic for the **Running the FSM** case, except for `ir` which remains `(true, er.inner)`.
/// - Output the calculated egress payload: `ep = Some(ep_f)`
/// - The case next cycle is determined by the logic: `sp_next = ...`
/// - The FSM state next cycle is determined by the logic: `s_next = ...`
/// - If not `flow`,
/// - Save the ingress payload to transition to the **Running the FSM** case next cycle: `sp_next = ip`
/// - Start a new FSM with the initial state next cycle: `s_next = init`
/// - If no ingress transfer happens (`else`),
/// - Remain in the current case: `sp_next = sp`
/// - Do not change the FSM state: `s_next = s`
/// - **Running the FSM** (`sp == Some`)
/// - Run `f`: `let (ep_f, s_next_f, is_last) = f(sp.unwrap(), s)`
/// - Output the calculated egress payload: `ep = Some(ep_f)`
/// - (Let's say that "the FSM finishes" if an egress transfer happens and this is the last state of the FSM
/// (`et && is_last`).)
/// - For the ingress resolver,
/// - If `pipe`, do not accept a new ingress payload but can accept one if the FSM finishes:
/// `ir = (et && is_last, er.inner)`
/// - If not `pipe`, do not accept a new ingress payload: `ir = (false, er.inner)`
/// - If the FSM finishes and an ingress transfer happens (`if it`),
/// - (Note that this can only happen if `pipe`.)
/// - Save the new ingress payload and remain in the current case: `sp_next = ip`
/// - Start a new FSM with the initial state next cycle: `s_next = init`
/// - If the FSM finishes but no ingress transfer happens (`if et && is_last`),
/// - Remove the saved payload to transition to the **Waiting for an ingress transfer** case next cycle:
/// `sp_next = None`
/// - Reset the FSM state next cycle: `s_next = init`
/// - If an egress transfer happens but this is not the last state of the FSM (`else if et`),
/// - Remain in the current case: `sp_next = sp`
/// - Update the FSM state next cycle: `s_next = s_next_f`
/// - If no egress transfer happens (`else`),
/// - Remain in the current case: `sp_next = sp`
/// - Do not update the FSM state: `s_next = s`
pub fn fsm_egress<EP: Copy, S: Copy>(
self,
init: S,
pipe: bool,
flow: bool,
f: impl Fn(P, S) -> (EP, S, bool),
) -> I<VrH<EP, R>, D> {
self.map_resolver_inner::<(R, (HOption<P>, S))>(|(r, _)| r).transparent_fsm_egress(init, pipe, flow, f)
}
/// For each transferred ingress payload, runs a finite state machine described by `f` until `f` returns true for
/// `is_last`. Specifically, this version of the combinator allows you to access the egress resolver while running
/// the FSM.
///
/// This allows you to process each ingress payload using multiple FSM states.
///
/// - Payload: Controlled by the combinator's behavior.
/// - Resolver: The ingress ready signal is controlled by the combinator's behavior. The inner value `R` of the
/// resolver is preserved.
///
/// | Interface | Ingress | Egress |
/// | :-------: | ------------ | ------------- |
/// | **Fwd** | `HOption<P>` | `HOption<EP>` |
/// | **Bwd** | `Ready<R>` | `Ready<R>` |
///
/// # Detailed explanation
///
/// ## Parameters
///
/// - `init`: The initial state for the FSM.
/// - `f`: The function that describes the FSM. If `let (ep, s_next, is_last) = f(p, er_inner, s)`,
/// - `p`: The current saved ingress payload for this FSM.
/// - `er_inner`: The inner value of the egress resolver.
/// - `s`: The current FSM state.
/// - `ep`: The calculated egress payload.
/// - `s_next`: The next FSM state.
/// - `is_last`: Whether this is the last state of the FSM for the current saved payload.
///
/// ## High-level overview of the behavior
///
/// The combinator can be in one of the two cases: **Waiting for an ingress transfer** and **Running the FSM**.
///
/// Initially, the combinator is in the **Waiting for an ingress transfer** case and waits for an ingress transfer
/// to happen. Once an ingress transfer happens, it saves the ingress payload to transition to the **Running the
/// FSM** case, and starts a new FSM.
///
/// In the **Running the FSM** case, the combinator runs the FSM with the saved payload, outputting egress payloads.
/// When `f` returns true for `is_last`, it will transition back to the **Waiting for an ingress transfer**
/// case next cycle.
///
/// ## Detailed behavior
///
/// > NOTE: The description below assumes the following naming convention. Here, `sp` is the saved ingress payload
/// > and determines the case the combinator is in. `s` is the FSM state. The description is organized sligtly
/// > differently from the actual implementation for better clarity.
/// >
/// > ```ignore
/// > // an implementation of `fsm_egress_with_r`
/// > self.fsm((None, init), |ip, er, (sp, s)| {
/// > // ... the description below would fit here
/// > (ep, ir, (sp_next, s_next))
/// > })
/// > ```
///
/// - **Waiting for an ingress transfer** (`sp == None`)
/// - Do not produce an egress payload: `ep = None`
/// - Can accept a new ingress payload: `ir = (true, er.inner)`
/// - If an ingress transfer happens (`if it`),
/// - Save the ingress payload and transit to the **Running the FSM** case next cycle: `sp_next = ip`
/// - Start a new FSM with the initial state next cycle: `s_next = init`
/// - **Running the FSM** (`sp == Some`)
/// - Run `f`: `let (ep_f, s_next_f, is_last) = f(sp.unwrap(), er.inner, s)`
/// - Output the calculated egress payload: `ep = Some(ep_f)`
/// - Let's say that "the FSM finishes" if an egress transfer happens and this is the last state of the FSM
/// (`et && is_last`).
/// - Do not accept a new ingress payload, but can accept one if the FSM finishes: `ir = (et && is_last, er.inner)`
/// - If the FSM finishes and an ingress transfer happens (`if it`),
/// - Save the new ingress payload and remain in the current case: `sp_next = ip`
/// - Start a new FSM with the initial state next cycle: `s_next = init`
/// - If the FSM finishes but no ingress transfer happens (`if et && is_last`),
/// - Remove the saved payload to transition to the **Waiting for an ingress transfer** case next cycle: `sp_next = None`
/// - Reset the FSM state next cycle: `s_next = init`
/// - If an egress transfer happens but this is not the last state of the FSM (`else if et`),
/// - Remain in the current case: `sp_next = sp`
/// - Update the FSM state next cycle: `s_next = s_next_f`
/// - If no egress transfer happens (`else`),
/// - Remain in the current case: `sp_next = sp`
/// - Do not update the FSM state: `s_next = s`
pub fn fsm_egress_with_r<EP: Copy, S: Copy>(
self,
init: S,
pipe: bool,
f: impl Fn(P, R, S) -> (EP, S, bool),
) -> I<VrH<EP, R>, { Dep::Demanding }> {
self.map_resolver_inner(|er_inner: (R, HOption<P>)| er_inner.0).transparent_fsm_egress_with_r(init, pipe, f)
}
}
// TODO: Change `(HOption<P>, S)` to `HOption<(P, S)>`? It's not the actual type of the internal state but it better
// represents the semantics.
impl<P: Copy, R: Copy, S: Copy, const D: Dep> I<VrH<P, (R, (HOption<P>, S))>, D> {
/// A variation of [`I::fsm_egress`] that additionally outputs the internal state to the ingress resolver.
///
/// - Payload: The same behavior as [`I::fsm_egress`].
/// - Resolver: The same behavior as [`I::fsm_egress`], but additionally the internal state `(HOption<P>, S)` is
/// outputted.
///
/// | Interface | Ingress | Egress |
/// | :-------: | ----------------------------- | ------------- |
/// | **Fwd** | `HOption<P>` | `HOption<EP>` |
/// | **Bwd** | `Ready<(R, (HOption<P>, S))>` | `Ready<R>` |
pub fn transparent_fsm_egress<EP: Copy>(
self,
init: S,
pipe: bool,
flow: bool,
f: impl Fn(P, S) -> (EP, S, bool),
) -> I<VrH<EP, R>, D> {
unsafe {
self.fsm::<(HOption<P>, S), D, VrH<EP, R>>((None, init), |ip, er, (sp, s)| {
let (ep, s_next, is_last) = if let Some(p) = sp {
let (ep, s_next, is_last) = f(p, s);
(Some(ep), s_next, is_last)
} else if flow && ip.is_some() && sp.is_none() {
let (ep, s_next, is_last) = f(ip.unwrap(), init);
(Some(ep), s_next, is_last)
} else {
(None, s, false)
};
let et = ep.is_some() && er.ready;
let ir = Ready::new(sp.is_none() || (et && is_last && pipe), (er.inner, (sp, s)));
let it = ip.is_some() && ir.ready;
let (sp_next, s_next) = if flow && it && et && sp.is_none() {
if is_last {
(None, init)
} else {
(ip, s_next)
}
} else if it {
(ip, init)
} else if et && is_last {
(None, init)
} else if et {
(sp, s_next)
} else {
(sp, s)
};
(ep, ir, (sp_next, s_next))
})
}
}
}
impl<P: Copy, R: Copy, const D: Dep> I<VrH<P, (R, HOption<P>)>, D> {
/// TODO: Documentation
pub fn transparent_fsm_egress_with_r<EP: Copy, S: Copy>(
self,
init: S,
pipe: bool,
f: impl Fn(P, R, S) -> (EP, S, bool),
) -> I<VrH<EP, R>, { Dep::Demanding }> {
unsafe {
self.fsm::<(HOption<P>, S), { Dep::Demanding }, VrH<EP, R>>((None, init), |ip, er, (sp, s)| {
let (ep, s_next, is_last) = if let Some(p) = sp {
let (ep, s_next, is_last) = f(p, er.inner, s);
(Some(ep), s_next, is_last)
} else {
(None, s, false)
};
let et = ep.is_some() && er.ready;
let ir = Ready::new(sp.is_none() || (et && is_last && pipe), (er.inner, sp));
let it = ip.is_some() && ir.ready;
let (sp_next, s_next) = if it {
(ip, init)
} else if et && is_last {
(None, init)
} else if et {
(sp, s_next)
} else {
(sp, s)
};
(ep, ir, (sp_next, s_next))
})
}
}
}