Date   : Thu, 03 May 2001 08:10:57 +0000
From   : "W.H.Scholten" <s_whs@...>
Subject: bbctape: tape images

L.S.

I fixed the problem I mentioned in my previous mail, but the program
needs more refinements (proper silence detection).

At the moment bbctape 0.95 only supports raw tape images (single
bitstream, no silence/noise delays yet). I've tested this on fortress (3
standard format files, then a custom format stream), making a tape dump
(result is about 56K, which includes the header tones, start/stop bits)
of a raw file (which was about 17MB).

I've written this tape image back to a raw file and directly to the BBC
which loaded it and ran. It seems to work!

Here's the format I intend to use to also support silence delays:

Tape image format:
 * id: "BBCTAPE" + terminating 0
 * followed by data blocks which consist of:
 *  byte  0 : block type:
 *  bytes 1 - 4 : block len (MSB)
 *  bytes 5 - <block_len-1> : data
 *
 * block type = 0 : silence
 *     - 4 bytes : MSB block length (=1+4+4)
 *     - 4 bytes : MSB duration (ms)
 *
 * block type = 1 : bit stream:
 *     - 4 bytes : MSB block length (=1+4+2+ (<nbits> +7)/8)
 *     - 2 bytes : MSB tone frequency (Hz) (= baud rate)
 *     - 4 bytes : MSB number of bits in the block
 *     - [ (<nbits> +7)/8 ]: data block with the bits
 *
 * block type = 2 : standard BBC tape block
 *     - 4 bytes : MSB block length (=1+4+2+ <tape block size>)
 *     - 2 bytes : MSB tone frequency (Hz) (= baud rate)
 *     - [ tape block size ]: data block with the actual tape block

Comments?

Wouter