46 lines
2.2 KiB
Text
46 lines
2.2 KiB
Text
<<<
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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 MTIME is **not** implemented
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| Configuration generics: | _IO_MTIME_EN_ | implement MTIME 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 MTIME machine system timer that is compatible to the RISC-V
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privileged specifications. The 64-bit system time is accessed via the memory-mapped `TIME_LO` and
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`TIME_HI`registers. A 64-bit time compare register, which is accessible via the memory-mapped `TIMECMP_LO`
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and `TIMECMP_HI` registers, can be used to configure the CPU's MTI (machine timer interrupt). 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 `TIMECMP` again (either by modifying
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`TIME` or `TIMECMP`).
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.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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[IMPORTANT]
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The `mtime_irq_i` signal is level-triggered and high-active. Once set the signal has to stay high until
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the interrupt request is explicitly acknowledged (e.g. writing to a memory-mapped register). All RISC-V standard interrupts
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can **NOT** be acknowledged by writing zero to the according <<_mip>> CSR bit. +
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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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| `0xffffff90` | `NEORV32_MTIME.TIME_LO` | 31:0 | r/w | machine system time, low word
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| `0xffffff94` | `NEORV32_MTIME.TIME_HI` | 31:0 | r/w | machine system time, high word
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| `0xffffff98` | `NEORV32_MTIME.TIMECMP_LO` | 31:0 | r/w | time compare, low word
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| `0xffffff9c` | `NEORV32_MTIME.TIMECMP_HI` | 31:0 | r/w | time compare, high word
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|=======================
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