101 lines
3 KiB
Plaintext
101 lines
3 KiB
Plaintext
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(local util (require :lib.util))
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(local tape (require :asm.tape))
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; https://www.apple.asimov.net/documentation/hardware/io/The%20Apple%20II%20Cassette%20Interface.txt
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; header
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; ---+ +-------------+ +-----+
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; | | | | |
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; +-------------+ +----+ |
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; | 1300 microseconds | 200| 250 |
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; header tone | synchronous bit |
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; 0 and 1 bits
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; +-----+ +----------+ +
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; | | | | |
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; + +-----+ +----------+
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; | 500 usec | 1000 usec |
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(local samplerate 48000)
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(fn us-to-s [us] (* (/ 1 1000000) us))
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(fn samplecount [us] (* samplerate (us-to-s us)))
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(fn checksum [bytes]
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(var sum 0xff)
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(for [ibyte 1 (bytes:len)]
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(set sum (bit.bxor sum (: (bytes:sub ibyte ibyte) :byte))))
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sum)
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(fn data []
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{:cycles []
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:samples 0
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:cycle
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(fn [self us count]
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(local samples (samplecount us))
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(local prev-cycle (. self.cycles (length self.cycles)))
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(local prev-samples (-?> prev-cycle (. 1)))
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(if (= samples prev-samples) (tset prev-cycle 2 (+ (. prev-cycle 2) count))
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(table.insert self.cycles [samples count]))
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(set self.samples (+ self.samples (* samples count))))
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:header
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(fn [self ?s]
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(self:cycle (/ 1300 2) (math.floor (/ (or ?s 5) (us-to-s (/ 1300 2)))))
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(self:cycle 200 1)
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(self:cycle 250 1))
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:bit (fn [self on] (self:cycle (if on 500 250) 2))
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:byte
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(fn [self byte]
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(for [ibit 7 0 -1]
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(self:bit (not= (bit.band byte (bit.lshift 1 ibit)) 0))))
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:bytes
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(fn [self bytes]
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(for [ibyte 1 (bytes:len)]
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(self:byte (: (bytes:sub ibyte ibyte) :byte))))
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:bytes-with-checksum
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(fn [self bytes]
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(self:bytes bytes)
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(self:byte (checksum bytes)))
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:to-sound
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(fn [self]
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(local sound (love.sound.newSoundData (+ self.samples (samplecount 8500)) samplerate 16 1))
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(var isample 0)
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(var err 0)
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(var on true)
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(each [_ [samples count] (ipairs self.cycles)]
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(for [_ 1 count]
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(set err (+ err (% samples 1)))
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(for [_ 1 (+ samples (math.floor err))]
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(sound:setSample isample (if on 0.75 -0.75))
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(set isample (+ isample 1)))
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(set err (% err 1))
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(set on (not on))))
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; finish last bit
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(set on (not on))
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(for [_ 1 (samplecount 500)]
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(sound:setSample isample (if on 0.75 -0.75))
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(set isample (+ isample 1)))
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; add a little pad of zeros
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(for [_ 1 (samplecount 8000)]
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(sound:setSample isample 0)
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(set isample (+ isample 1)))
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sound)})
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(fn gen-bin [bytes ?s-header]
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(local dat (data))
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(dat:header ?s-header)
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(dat:bytes-with-checksum bytes)
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(dat:to-sound))
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(fn gen-basic [bytes ?s-header]
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(local dat (data))
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(dat:header ?s-header)
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(dat:bytes-with-checksum
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(.. (util.int16-to-bytes (+ (bytes:len) 1)) (util.int8-to-bytes 0xd5)))
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(dat:header ?s-header)
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(dat:bytes-with-checksum bytes)
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(dat:to-sound))
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{: gen-bin : gen-basic : checksum : data : samplerate : samplecount}
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