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Attempt some logical mapping.

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This commit is contained in:
Thomas Harte 2024-03-06 21:51:19 -05:00
parent 4059905f85
commit 691a42d81e
1 changed files with 116 additions and 17 deletions
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133
Machines/Acorn/Archimedes/Archimedes.cpp
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@ -261,41 +261,140 @@ struct Memory {
// from the other.
// Physical to logical mapping.
uint32_t pages_[128]{};
std::array<uint32_t, 128> pages_{};
// Logical to physical mapping.
struct MappedPage {
uint8_t *target = nullptr;
uint8_t protection_level = 0;
};
MappedPage mapping_[8192];
std::array<MappedPage, 8192> mapping_;
template <typename IntT, bool is_read>
IntT *logical_ram(uint32_t address, InstructionSet::ARM::Mode) {
// TODO: (1) which logical page is this?
logger.error().append("TODO: Logical RAM mapping at %08x", address);
// logger.error().append("TODO: Logical RAM mapping at %08x", address);
// 4kb:
// A[6:0] -> PPN[6:0]
// A[11:10] -> LPN[12:11]; A[22:12] -> LPN[10:0]
address &= 0x1ff'ffff;
size_t page;
// 8kb:
// A[0] -> PPN[6]; A[6:1] -> PPN[5:0]
// A[11:10] -> LPN[11:10]; A[22:13] -> LPN[9:0]
// TODO: eliminate switch here.
switch(page_size_) {
default:
case PageSize::kb4:
page = address >> 12;
address &= 0x0fff;
break;
case PageSize::kb8:
page = address >> 13;
address &= 0x1fff;
break;
case PageSize::kb16:
page = address >> 14;
address &= 0x3fff;
break;
case PageSize::kb32:
page = address >> 15;
address &= 0x7fff;
break;
}
// 16kb:
// A[1:0] -> PPN[6:5]; A[6:2] -> PPN[4:0]
// A[11:10] -> LPN[10:9]; A[22:14] -> LPN[8:0]
if(!mapping_[page].target) {
return nullptr;
}
// 32kb:
// A[1] -> PPN[6]; A[2] -> PPN[5]; A[0] -> PPN[4]; A[6:3] -> PPN[6:3]
// A[11:10] -> LPN[9:8]; A[22:15] -> LPN[7:0]
// TODO: consider protection level.
return nullptr;
return reinterpret_cast<IntT *>(mapping_[page].target + address);
}
void update_mapping() {
logger.error().append("TODO: Update logical RAM mapping");
logger.info().append("Updated logical RAM mapping");
// For each physical page, project it into logical space.
switch(page_size_) {
default:
case PageSize::kb4: update_mapping<PageSize::kb4>(); break;
case PageSize::kb8: update_mapping<PageSize::kb8>(); break;
case PageSize::kb16: update_mapping<PageSize::kb16>(); break;
case PageSize::kb32: update_mapping<PageSize::kb32>(); break;
}
}
template <PageSize size>
void update_mapping() {
// Clear all logical mappings.
std::fill(mapping_.begin(), mapping_.end(), MappedPage{});
const auto bits = [](int start, int end) -> uint32_t {
return ((1 << start) - 1) - ((1 << end) - 1);
};
// For each physical page, project it into logical space
// and store it.
for(const auto page: pages_) {
uint32_t physical, logical;
switch(size) {
case PageSize::kb4:
// 4kb:
// A[6:0] -> PPN[6:0]
// A[11:10] -> LPN[12:11]; A[22:12] -> LPN[10:0] i.e. 8192 logical pages
physical = page & bits(6, 0);
physical <<= 12;
logical = (page & bits(11, 10)) << 1;
logical |= (page & bits(22, 12)) >> 12;
break;
case PageSize::kb8:
// 8kb:
// A[0] -> PPN[6]; A[6:1] -> PPN[5:0]
// A[11:10] -> LPN[11:10]; A[22:13] -> LPN[9:0] i.e. 4096 logical pages
physical = (page & bits(0, 0)) << 6;
physical |= (page & bits(6, 1)) >> 1;
physical <<= 13;
logical = page & bits(11, 10);
logical |= (page & bits(22, 13)) >> 13;
break;
case PageSize::kb16:
// 16kb:
// A[1:0] -> PPN[6:5]; A[6:2] -> PPN[4:0]
// A[11:10] -> LPN[10:9]; A[22:14] -> LPN[8:0] i.e. 2048 logical pages
physical = (page & bits(1, 0)) << 5;
physical |= (page & bits(6, 2)) >> 2;
physical <<= 14;
logical = (page & bits(11, 10)) >> 1;
logical |= (page & bits(22, 14)) >> 14;
break;
case PageSize::kb32:
// 32kb:
// A[1] -> PPN[6]; A[2] -> PPN[5]; A[0] -> PPN[4]; A[6:3] -> PPN[6:3]
// A[11:10] -> LPN[9:8]; A[22:15] -> LPN[7:0] i.e. 1024 logical pages
physical = (page & bits(1, 1)) << 5;
physical |= (page & bits(2, 2)) << 3;
physical |= (page & bits(0, 0)) << 4;
physical |= page & bits(6, 3);
physical <<= 15;
logical = (page & bits(11, 10)) >> 2;
logical |= (page & bits(22, 15)) >> 15;
break;
}
// TODO: consider clashes.
// TODO: what if there's less than 4mb present?
mapping_[logical].target = &ram_[physical];
mapping_[logical].protection_level = (page >> 8) & 3;
}
}
};