read.cc

来自「一个mips虚拟机非常好代码,使用C++来编写的,希望大家多学学,」· CC 代码 · 共 51 行

#include <string.h>
#include <assert.hh>
#include <inttypes.hh>
#include "rtc.hh"


ClockValue
MT48Tx2::read(UInt64 addr, UInt64* buf, int size)
{
    assert(size > 0 && size <= 8);
    assert(!is_power_of_two(size) || (addr & (size - 1)) == 0);

    // Decode the address. Note that, as with real hardware, we simply ignore
    // irrelevant address lines (the hardware has no way of knowing where in
    // the address space it is currently mapped.)

    addr %= 2*KB;

    if (addr + size > CONTROL) {
	if ((addr + size > CONTROL + 1) && !bit(data[CONTROL], 6)) {
	    msg("RTC read without halting.");
	    update_read(bus->clock);
	}
    }

    // Fetch the data.
    if (size == sizeof(UInt8))
	*buf = *(UInt8 *)(data + addr);
    else if (size == sizeof(UInt16))
	*buf = *(UInt16 *)(data + addr);
    else if (size == sizeof(UInt32))
	*buf = *(UInt32 *)(data + addr);
    else if (size == sizeof(UInt64))
	*buf = *(UInt64 *)(data + addr);
    else {
	// Forget about performance.
	memcpy(buf, data + addr, size);
	if (big_endian_host())
	    *buf >>= (sizeof(*buf) - size) * 8;
    }

    // Compute the access latency.

    if (freq != bus->clock->freq) {
	read_latency = bus->clock->cycles(read_latency, freq);
	write_latency = bus->clock->cycles(write_latency, freq);
	freq = bus->clock->freq;
    }
    return read_latency * size;
}