Confused about ADT protocol

[Kevin]

GET and PUT seem to be making my head spin

put states

Apple sends:
One byte: "Z" ($DA)
Byte stream: file name (null terminated)

Host sends:
Two bytes: file size in blocks (LSB, MSB)
One byte: return code:
$00 = File exists (and file size is valid)
$02 = File does not exist
$04 = File exists, not recognized as a valid disk image

if the disk is coming from the apple how is the host going to find a file, measure its size and check for being valid? SO I am wondering if that could be backwards, what else might be?

Thanks

[David Schmidt]

On 11/18/2012 4:34 PM, Kevin wrote:
> put states
>
> Apple sends:
> One byte: "Z" ($DA)
> Byte stream: file name (null terminated)
>
> Host sends:
> Two bytes: file size in blocks (LSB, MSB)
> One byte: return code:
> $00 = File exists (and file size is valid)
> $02 = File does not exist
> $04 = File exists, not recognized as a valid disk image
>
> if the disk is coming from the apple how is the host going to find a file, measure its size and check for being valid?

Some history for you: in the beginning there was ADT, and there was only
the "S" flow to send a disk. It unconditionally sent the file, with no
concern as to whether or not the file existed on the host. It would
fail with unable to write, or overwrite without confirmation; I don't
remember which, but both situations were bad.

ADTPro came along, and "P" was introduced. That essentially implemented
the same (broken) semantics, though the flow has different contents. It
positively overwrote whatever happened to be there with the same file name.

So an extension was born: the "Z" flow. This is all transparent to the
user; the Z and P are combined into one logical flow. You'll see both
mushed together on the protocol section just below what you cited. What
happens with "Z" is that the proposed filename is sent to the host, and
the host replies back with a file size (which is really ignored - it
would be zero if no file existed) and a return code that indicates if
the file already exists or not. That gives us the chance to ask the
user if they want to overwrite or not, if necessary. If the user wants
to overwrite, or if there is no file to overwrite, then the put proceeds
apace.

> SO I am wondering if that could be backwards, what else might be?

No one ever promised it was right... ;-)

[Kevin]

OK I see now thanks a bunch

[Kevin]

and if you missed one of my crazy updates what I am doing is implementing the ADT host on my micro-controller so it would have

VSDRIVE <- done
ADTPro <- 25% done
and maybe AGS if it quits giving me fits <- not started, may have to go to version 1.something due to ram restrictions

into a nice little beige box with a SD card sticking out the front, since the amount of ram I NEED for FAT16/32 support is more or less stuck with a chip with 4x the amount of ROM that I need ... might as well "fill her up"