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@@ -3,6 +3,8 @@
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Kendryte K210 is a dual-core RISC-V RV64GC chip with hardware accelerated AI peripheral.
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According to its manual, K210 is taped out in TSMC 7nm and can speed up to 400MHz.
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+## Implementation details
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+
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The K210 SoC implements version 1.9.1 of RISC-V's privileged specification.
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This version differents from latest version (by current version 1.11) in the following aspects:
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@@ -20,3 +22,39 @@ Machine external handler and timer set calls is modified to meet the requirement
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interrupt handlers.
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If there are mistakes or missing features in current support module, we welcome further contributions!
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+
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+## Private SBI functions
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+
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+To solve the issue 3 in previous section, RustSBI's current implementation includes a RustSBI specific
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+SBI call as a function.
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+
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+The K210 supervisor-level external interrupt handler register function is declared as:
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+
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+```rust
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+fn sbi_rustsbi_k210_sext(phys_addr: usize) -> SbiRet;
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+```
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+
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+This function registers a device interrupt handler to machine level environment.
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+On any machine-level external interrupt, the RustSBI's K210 environment would call the function provided.
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+
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+The function's physical address shall be stored in register `a0` before calling this function.
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+RustSBI will regard `a0` as a function wiout any parameters and any return values, or a `phys_addr: fn()`.
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+
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+This function will always return `SbiRet` value of `SBI_SUCCESS`.
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+
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+### Function Listing
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+
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+According to RISC-V SBI specification:
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+
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+> Firmware Code Base Specific SBI Extension Space, Extension Ids 0x0A000000 through 0x0AFFFFFF
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+>
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+> Low bits is SBI implementation ID. The firmware code base SBI extension is the additional SBI extensions to SBI
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+> implementation. That provides the firmware code base specific SBI functions which are defined in the external
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+> firmware specification.
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+
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+Since RustSBI has the implementation ID 4, its specific SBI extension is `0x0A000004`. We add a function
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+to this specific SBI extension.
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+
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+| Function Name | Function ID | Extension ID |
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+|:-----|:----|:----|
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+| sbi_rustsbi_k210_sext | 0x210 | 0x0A000004 |
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