void
mem_init(void)
{
if (!cpu_onboot()) // only do once, on the boot CPU
return;
// Determine how much base (<640K) and extended (>1MB) memory
// is available in the system (in bytes),
// by reading the PC's BIOS-managed nonvolatile RAM (NVRAM).
// The NVRAM tells us how many kilobytes there are.
// Since the count is 16 bits, this gives us up to 64MB of RAM;
// additional RAM beyond that would have to be detected another way.
size_t basemem = ROUNDDOWN(nvram_read16(NVRAM_BASELO)*1024, PAGESIZE);
size_t extmem = ROUNDDOWN(nvram_read16(NVRAM_EXTLO)*1024, PAGESIZE);
warn("Assuming we have 1GB of memory!");
extmem = 1024*1024*1024 - MEM_EXT; // assume 1GB total memory
// The maximum physical address is the top of extended memory.
mem_max = MEM_EXT + extmem;
// Compute the total number of physical pages (including I/O holes)
mem_npage = mem_max / PAGESIZE;
cprintf("Physical memory: %dK available, ", (int)(mem_max/1024));
cprintf("base = %dK, extended = %dK\n",
(int)(basemem/1024), (int)(extmem/1024));
spinlock_init(&_freelist_lock);
pageinfo *mem_pageinfo = (pageinfo*)ROUNDUP((uint32_t)end, (uint32_t)sizeof(pageinfo));
memset(mem_pageinfo, 0, sizeof(pageinfo)*mem_npage);
pageinfo **freetail = &mem_freelist;
int i;
// Pages 0 and 1 are reserved.
for (i = 2; i < mem_npage; i++) {
// All of base memory otherwise is free after the kernel
// and the pageinfo table all memory should be free
if(i < basemem/4096 ||
i >= (uint32_t)(ROUNDUP(&mem_pageinfo[mem_npage],4096))/4096) {
// A free page has no references to it.
mem_pageinfo[i].refcount = 0;
// Add the page to the end of the free list.
*freetail = &mem_pageinfo[i];
freetail = &mem_pageinfo[i].free_next;
}
}
*freetail = NULL; // null-terminate the freelist
// Check to make sure the page allocator seems to work correctly.
mem_check();
}
void
main_console (void *data)
{
/* Read parameters from NVRAM. */
nvram_init ();
reset_counter = nvram_read16 (0);
/* Increment reset counter. */
++reset_counter;
/* Write reset counter to NVRAM. */
nvram_unprotect (&timer);
nvram_write16 (0, reset_counter);
nvram_protect (&timer);
for (;;)
tcl_main ((stream_t*) &uart);
}
void
mem_init(void)
{
if (!cpu_onboot()) // only do once, on the boot CPU
return;
// Determine how much base (<640K) and extended (>1MB) memory
// is available in the system (in bytes),
// by reading the PC's BIOS-managed nonvolatile RAM (NVRAM).
// The NVRAM tells us how many kilobytes there are.
// Since the count is 16 bits, this gives us up to 64MB of RAM;
// additional RAM beyond that would have to be detected another way.
size_t basemem = ROUNDDOWN(nvram_read16(NVRAM_BASELO)*1024, PAGESIZE);
size_t extmem = ROUNDDOWN(nvram_read16(NVRAM_EXTLO)*1024, PAGESIZE);
warn("Assuming we have 1GB of memory!");
extmem = 1024*1024*1024 - MEM_EXT; // assume 1GB total memory
// The maximum physical address is the top of extended memory.
mem_max = MEM_EXT + extmem;
// Compute the total number of physical pages (including I/O holes)
mem_npage = mem_max / PAGESIZE;
cprintf("Physical memory: %dK available, ", (int)(mem_max/1024));
cprintf("base = %dK, extended = %dK\n",
(int)(basemem/1024), (int)(extmem/1024));
// Insert code here to:
// (1) allocate physical memory for the mem_pageinfo array,
// making it big enough to hold mem_npage entries.
// (2) add all pageinfo structs in the array representing
// available memory that is not in use for other purposes.
//
// For step (2), here is some incomplete/incorrect example code
// that simply marks all mem_npage pages as free.
// Which memory is actually free?
// 1) Reserve page 0 for the real-mode IDT and BIOS structures
// (do not allow this page to be used for anything else).
// 2) Reserve page 1 for the AP bootstrap code (boot/bootother.S).
// 3) Mark the rest of base memory as free.
// 4) Then comes the IO hole [MEM_IO, MEM_EXT).
// Mark it as in-use so that it can never be allocated.
// 5) Then extended memory [MEM_EXT, ...).
// Some of it is in use, some is free.
// Which pages hold the kernel and the pageinfo array?
// Hint: the linker places the kernel (see start and end above),
// but YOU decide where to place the pageinfo array.
// Change the code to reflect this.
pageinfo **freetail = &mem_freelist;
int i;
for (i = 0; i < mem_npage; i++) {
// A free page has no references to it.
mem_pageinfo[i].refcount = 0;
// Add the page to the end of the free list.
*freetail = &mem_pageinfo[i];
freetail = &mem_pageinfo[i].free_next;
}
*freetail = NULL; // null-terminate the freelist
// ...and remove this when you're ready.
panic("mem_init() not implemented");
// Check to make sure the page allocator seems to work correctly.
mem_check();
}
