write.cc

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,

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


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

    // Decode the address. See also the comment in "read.cc".

    addr %= 2*KB;

    // Cache the control register in case it gets changed.

    UInt8 old_control = data[CONTROL];

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

    // Handle register accesses.

    UInt8 new_control = data[CONTROL];

    if (addr + size > CONTROL) {
	if ((addr + size > CONTROL + 1) && !bit(old_control, 7))
	    msg("RTC written without halting.");
	if (old_control != new_control) {
	    if (bit(old_control, 7) && !bit(new_control, 7))
		update_write(bus->clock); // write bit cleared; set the clock
	    if (!bit(old_control, 6) && bit(new_control, 6))
		update_read(bus->clock); // read bit set; halt the clock
	}
    }

    // Compute the access latency. This chip is strictly 8-bit only,
    // so the overhead is paid once for every byte read.

    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 write_latency * size;
}