From 7994148f558acbdaccd8e1c50ad41ad6727fa1e1 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Mon, 15 Aug 2016 22:10:53 -0400
Subject: [PATCH] I'm starting to make a little headway, I think: this performs
lead-ins and countdowns, though with no actual data or anything as helpful as
that.
---
Storage/Tape/Formats/TapePRG.cpp | 54 ++++++++++++++++++++++++++++++--
Storage/Tape/Formats/TapePRG.hpp | 7 +++--
2 files changed, 57 insertions(+), 4 deletions(-)
diff --git a/Storage/Tape/Formats/TapePRG.cpp b/Storage/Tape/Formats/TapePRG.cpp
index 6c1370cdf..cb648e3c6 100644
--- a/Storage/Tape/Formats/TapePRG.cpp
+++ b/Storage/Tape/Formats/TapePRG.cpp
@@ -12,7 +12,7 @@
using namespace Storage;
-TapePRG::TapePRG(const char *file_name) : _file(nullptr), _bitPhase(3)
+TapePRG::TapePRG(const char *file_name) : _file(nullptr), _bitPhase(3), _filePhase(FilePhaseLeadIn), _phaseOffset(0)
{
struct stat file_stats;
stat(file_name, &file_stats);
@@ -64,9 +64,59 @@ void TapePRG::reset()
{
_bitPhase = 3;
fseek(_file, 2, SEEK_SET);
+ _filePhase = FilePhaseLeadIn;
+ _phaseOffset = 0;
}
void TapePRG::get_next_output_token()
{
- _outputToken = Leader;
+ // the lead-in is 20,000 instances of the lead-in pair; every other phase begins with 5000
+ // before doing whatever it should be doing
+ if(_filePhase == FilePhaseLeadIn || _phaseOffset < 5000)
+ {
+ _outputToken = Leader;
+ _phaseOffset++;
+ if(_filePhase == FilePhaseLeadIn && _phaseOffset == 20000)
+ {
+ _phaseOffset = 0;
+ _filePhase = FilePhaseHeader;
+ }
+ return;
+ }
+
+ // determine whether a new byte needs to be queued up
+ int block_offset = _phaseOffset - 5000;
+ int bit_offset = block_offset % 10;
+ int byte_offset = block_offset / 10;
+
+ if(bit_offset == 0)
+ {
+ // the first nine bytes are countdown; the high bit is set if this is a header
+ if(byte_offset < 9)
+ {
+ _output_byte = (uint8_t)(9 - block_offset) | 0x80;
+ }
+ else
+ {
+ }
+ }
+
+ switch(bit_offset)
+ {
+ case 0:
+ _outputToken = WordMarker;
+ break;
+ default:
+ _outputToken = (_output_byte & (1 << (bit_offset - 1))) ? One : Zero;
+ break;
+ case 1:
+ {
+ uint8_t parity = _outputToken;
+ parity ^= (parity >> 4);
+ parity ^= (parity >> 2);
+ parity ^= (parity >> 1);
+ _outputToken = (parity&1) ? One : Zero;
+ }
+ break;
+ }
}
diff --git a/Storage/Tape/Formats/TapePRG.hpp b/Storage/Tape/Formats/TapePRG.hpp
index 44493437f..100982f82 100644
--- a/Storage/Tape/Formats/TapePRG.hpp
+++ b/Storage/Tape/Formats/TapePRG.hpp
@@ -42,17 +42,20 @@ class TapePRG: public Tape {
enum FilePhase {
FilePhaseLeadIn,
- FilePhaseHeader
+ FilePhaseHeader,
+ FilePhaseData,
} _filePhase;
+ int _phaseOffset;
int _bitPhase;
enum OutputToken {
Leader,
Zero,
One,
- WordMarker
+ WordMarker,
} _outputToken;
void get_next_output_token();
+ uint8_t _output_byte;
};
}