48 lines
2.3 KiB
Plaintext
48 lines
2.3 KiB
Plaintext
<<<
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:sectnums:
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==== Machine System Timer (MTIME)
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[cols="<3,<3,<4"]
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[frame="topbot",grid="none"]
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|=======================
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| Hardware source file(s): | neorv32_mtime.vhd |
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| Software driver file(s): | neorv32_mtime.c |
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| | neorv32_mtime.h |
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| Top entity port: | `mtime_irq_i` | RISC-V machine timer IRQ if internal one is **not** implemented
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| | `mtime_time_o` | Current system time (`TIME` register)
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| Configuration generics: | `IO_MTIME_EN` | implement machine timer when `true`
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| CPU interrupts: | `MTI` | machine timer interrupt (see <<_processor_interrupts>>)
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|=======================
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The MTIME module implements a memory-mapped machine system timer that is compatible to the RISC-V
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privileged specifications. The 64-bit system time is accessed via individual `TIME_LO` and
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`TIME_HI` registers. A 64-bit time compare register, which is accessible via individual `TIMECMP_LO`
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and `TIMECMP_HI` registers, can be used to configure the CPU's machine timer interrupt (`MTI`)). The interrupt
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is triggered whenever `TIME` (high & low part) is greater than or equal to `TIMECMP` (high & low part).
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The interrupt remains active (=pending) until `TIME` becomes less than `TIMECMP` again (either by modifying
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`TIME` or `TIMECMP`). The current system time is available for other SoC modules via the top's `mtime_time_o` signal.
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.Hardware Reset
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[NOTE]
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After a hardware reset the `TIME` and `TIMECMP` register are reset to all-zero.
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.External MTIME Interrupt
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[NOTE]
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If the internal MTIME module is disabled (`IO_MTIME_EN` = `false`) the machine timer interrupt becomes available
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as external signal. The `mtime_irq_i` signal is level-triggered and high-active. Once set the signal has to stay
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high until the interrupt request is explicitly acknowledged (e.g. writing to a user-defined memory-mapped register).
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**Register Map**
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.MTIME register map (`struct NEORV32_MTIME`)
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[cols="<3,<3,^1,^1,<6"]
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[options="header",grid="all"]
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|=======================
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| Address | Name [C] | Bits | R/W | Function
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| `0xfffff400` | `TIME_LO` | 31:0 | r/w | system time, low word
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| `0xfffff404` | `TIME_HI` | 31:0 | r/w | system time, high word
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| `0xfffff408` | `TIMECMP_LO` | 31:0 | r/w | time compare, low word
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| `0xfffff40c` | `TIMECMP_HI` | 31:0 | r/w | time compare, high word
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|=======================
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