neorv32/docs/datasheet/soc_mtime.adoc

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==== Machine System Timer (MTIME)
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|=======================
| Hardware source file(s): | neorv32_mtime.vhd |
| Software driver file(s): | neorv32_mtime.c |
| | neorv32_mtime.h |
| Top entity port: | `mtime_irq_i` | RISC-V machine timer IRQ if internal one is **not** implemented
| | `mtime_time_o` | Current system time (`TIME` register)
| Configuration generics: | `IO_MTIME_EN` | implement machine timer when `true`
| CPU interrupts: | `MTI` | machine timer interrupt (see <<_processor_interrupts>>)
|=======================
The MTIME module implements a memory-mapped machine system timer that is compatible to the RISC-V
privileged specifications. The 64-bit system time is accessed via individual `TIME_LO` and
`TIME_HI` registers. A 64-bit time compare register, which is accessible via individual `TIMECMP_LO`
and `TIMECMP_HI` registers, can be used to configure the CPU's machine timer interrupt (`MTI`)). The interrupt
is triggered whenever `TIME` (high & low part) is greater than or equal to `TIMECMP` (high & low part).
The interrupt remains active (=pending) until `TIME` becomes less than `TIMECMP` again (either by modifying
`TIME` or `TIMECMP`). The current system time is available for other SoC modules via the top's `mtime_time_o` signal.
.Hardware Reset
[NOTE]
After a hardware reset the `TIME` and `TIMECMP` register are reset to all-zero.
.External MTIME Interrupt
[NOTE]
If the internal MTIME module is disabled (`IO_MTIME_EN` = `false`) the machine timer interrupt becomes available
as external signal. The `mtime_irq_i` signal is level-triggered and high-active. Once set the signal has to stay
high until the interrupt request is explicitly acknowledged (e.g. writing to a user-defined memory-mapped register).
**Register Map**
.MTIME register map (`struct NEORV32_MTIME`)
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|=======================
| Address | Name [C] | Bits | R/W | Function
| `0xfffff400` | `TIME_LO` | 31:0 | r/w | system time, low word
| `0xfffff404` | `TIME_HI` | 31:0 | r/w | system time, high word
| `0xfffff408` | `TIMECMP_LO` | 31:0 | r/w | time compare, low word
| `0xfffff40c` | `TIMECMP_HI` | 31:0 | r/w | time compare, high word
|=======================