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Merge branch 'master' into EOI

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Thomas Harte 2023-12-12 12:15:13 -05:00
commit a49a3da21c
3 changed files with 75 additions and 69 deletions
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10
Components/DiskII/DiskII.cpp
View File

@ -23,8 +23,14 @@ DiskII::DiskII(int clock_rate) :
clock_rate_(clock_rate),
inputs_(input_command),
drives_{
Storage::Disk::Drive{clock_rate, 300, 1},
Storage::Disk::Drive{clock_rate, 300, 1}
// Bit of a hack here: drives are marginally slowed down compared to real drives
// in order to accomodate NIB files, which usually carry more data than will
// physically fit on a track once slip bits are reinserted.
//
// I don't like the coupling here.
// TODO: resolve better, somehow.
Storage::Disk::Drive{clock_rate, 295, 1},
Storage::Disk::Drive{clock_rate, 295, 1}
}
{
drives_[0].set_clocking_hint_observer(this);

125
Storage/Disk/DiskImage/Formats/NIB.cpp
View File

@ -55,95 +55,85 @@ long NIB::file_offset(Track::Address address) {
}
std::shared_ptr<::Storage::Disk::Track> NIB::get_track_at_position(::Storage::Disk::Track::Address address) {
// NIBs contain data for even-numbered tracks underneath a single head only.
// NIBs contain data for a fixed quantity of integer-position tracks underneath a single head only.
//
// Therefore:
// * reject any attempt to read from the second head;
// * treat 3/4 of any physical track as formatted, the remaining quarter as unformatted; and
// * reject any attempt to read beyond the defined number of tracks.
if(address.head) return nullptr;
if((address.position.as_quarter() & 3) == 3) return nullptr;
if(size_t(address.position.as_int()) >= number_of_tracks) return nullptr;
long offset = file_offset(address);
const long offset = file_offset(address);
std::vector<uint8_t> track_data;
{
std::lock_guard lock_guard(file_.get_file_access_mutex());
if(cached_offset_ == offset && cached_track_) {
return cached_track_;
}
file_.seek(offset, SEEK_SET);
track_data = file_.read(track_length);
}
// NIB files leave sync bytes implicit and make no guarantees
// about overall track positioning. My current best-guess attempt
// is to seek sector prologues then work backwards, inserting sync
// bits into [at most 5] preceding FFs. This is intended to put the
// Disk II into synchronisation just before each sector.
std::size_t start_index = 0;
std::set<size_t> sync_starts;
// Establish where syncs start by finding instances of 0xd5 0xaa and then regressing
// from each along all preceding FFs.
// about overall track positioning. The attempt works by locating
// any single run of FF that is sufficiently long and marking the last
// five as including slip bits.
std::set<size_t> sync_locations;
for(size_t index = 0; index < track_data.size(); ++index) {
// This is a D5 AA...
if(track_data[index] == 0xd5 && track_data[(index+1)%track_data.size()] == 0xaa) {
// ... count backwards to find out where the preceding FFs started.
size_t start = index - 1;
size_t length = 0;
while(track_data[start] == 0xff && length < 5) {
start = (start + track_data.size() - 1) % track_data.size();
++length;
// Count the number of FFs starting from here.
size_t length = 0;
size_t end = index;
while(track_data[end] == 0xff) {
end = (end + 1) % track_data.size();
++length;
}
// If that's at least five, regress and mark all as syncs.
if(length >= 5) {
for(int c = 0; c < 5; c++) {
end = (end + track_data.size() - 1) % track_data.size();
sync_locations.insert(end);
}
// Record a sync position only if there were at least five FFs, and
// sync only in the final five. One of the many crazy fictions of NIBs
// is the fixed track length in bytes, which is quite long. So the aim
// is to be as conservative as possible with sync placement.
if(length == 5) {
sync_starts.insert((start + 1) % track_data.size());
// If the apparent start of this sync area is 'after' the start, then
// this sync period overlaps position zero. So this track will start
// in a sync block.
if(start > index)
start_index = start;
}
// Experimental!! Permit only one run of sync locations.
// That should synchronise the Disk II to the nibble stream
// such that it remains synchronised from then on. At least,
// while this remains a read-only format.
break;
}
}
PCMSegment segment;
// If the track started in a sync block, write sync first.
if(start_index) {
segment += Encodings::AppleGCR::six_and_two_sync(int(start_index));
}
std::size_t index = start_index;
for(const auto location: sync_starts) {
// Write data from index to sync_start.
if(location > index) {
// This is the usual case; the only occasion on which it won't be true is
// when the initial sync was detected to carry over the index hole,
// in which case there's nothing to copy.
std::vector<uint8_t> data_segment(
track_data.begin() + ptrdiff_t(index),
track_data.begin() + ptrdiff_t(location));
segment += PCMSegment(data_segment);
std::size_t index = 0;
while(index < track_data.size()) {
// Deal with a run of sync values, if present.
const auto sync_start = index;
while(sync_locations.find(index) != sync_locations.end() && index < track_data.size()) {
++index;
}
if(index != sync_start) {
segment += Encodings::AppleGCR::six_and_two_sync(int(index - sync_start));
}
// Add a sync from sync_start to end of 0xffs, if there are
// any before the end of data.
index = location;
while(index < track_length && track_data[index] == 0xff)
// Deal with regular data.
const auto data_start = index;
while(sync_locations.find(index) == sync_locations.end() && index < track_data.size()) {
++index;
if(index - location)
segment += Encodings::AppleGCR::six_and_two_sync(int(index - location));
}
if(index != data_start) {
std::vector<uint8_t> data_segment(
track_data.begin() + ptrdiff_t(data_start),
track_data.begin() + ptrdiff_t(index));
segment += PCMSegment(data_segment);
}
}
// If there's still data remaining on the track, write it out. If a sync ran over
// the notional index hole, the loop above will already have completed the track
// with sync, so no need to deal with that case here.
if(index < track_length) {
std::vector<uint8_t> data_segment(
track_data.begin() + ptrdiff_t(index),
track_data.end());
segment += PCMSegment(data_segment);
}
return std::make_shared<PCMTrack>(segment);
std::lock_guard lock_guard(file_.get_file_access_mutex());
cached_offset_ = offset;
cached_track_ = std::make_shared<PCMTrack>(segment);
return cached_track_;
}
void NIB::set_tracks(const std::map<Track::Address, std::shared_ptr<Track>> &tracks) {
@ -194,4 +184,5 @@ void NIB::set_tracks(const std::map<Track::Address, std::shared_ptr<Track>> &tra
file_.seek(file_offset(track.first), SEEK_SET);
file_.write(track.second);
}
cached_track_ = nullptr; // Conservative, but safe.
}

9
Storage/Disk/DiskImage/Formats/NIB.hpp
View File

@ -11,6 +11,9 @@
#include "../DiskImage.hpp"
#include "../../../FileHolder.hpp"
#include "../../Track/PCMTrack.hpp"
#include <memory>
namespace Storage::Disk {
@ -33,6 +36,12 @@ class NIB: public DiskImage {
FileHolder file_;
long get_file_offset_for_position(Track::Address address);
long file_offset(Track::Address address);
// Cache for the last-generated track, given that head steps on an Apple II
// occur in quarter-track increments, so there'll routinely be four gets in
// a row for the same data.
long cached_offset_ = 0;
std::shared_ptr<Storage::Disk::PCMTrack> cached_track_;
};
}