{"id":628,"date":"2013-05-22T21:02:22","date_gmt":"2013-05-22T19:02:22","guid":{"rendered":"http:\/\/lallafa.de\/blog\/?p=628"},"modified":"2013-05-22T21:02:22","modified_gmt":"2013-05-22T19:02:22","slug":"emulating-plipbox-with-fs-uae","status":"publish","type":"post","link":"https:\/\/lallafa.de\/blog\/2013\/05\/emulating-plipbox-with-fs-uae\/","title":{"rendered":"Emulating plipbox with FS-UAE"},"content":{"rendered":"

Recently, I had some time to spend and wanted to work on the plipbox<\/a> project’s Amiga driver. Unfortunately, I only had my MacBook Pro with me and no\u00c2\u00a0Amiga or plipbox hardware.<\/p>\n

What does a SW developer do if the real hardware is not at hand?<\/p>\n

Yes, you write an emulator that represents the missing HW in SW on a machine\u00c2\u00a0you have access to…<\/p>\n

Adding a Virtual Parallel Port Protocol in FS-UAE<\/h3>\n

That said, I installed all required Amiga SW in a virtual environment in\u00c2\u00a0FS-UAE<\/a> on my Mac and soon I had my plipbox.device<\/strong> SANA II driver\u00c2\u00a0talking with the virtual parallel port in FS-UAE. What was missing now is a\u00c2\u00a0protocol that communicates the complete I\/O state from FS-UAE to another\u00c2\u00a0process. Then I could write a standalone application that does emulate the\u00c2\u00a0plipbox firmware and plipbox.device in FS-UAE would be operational.<\/p>\n

I defined a simple two-byte bi-directional protocol called vpar<\/a><\/strong> that\u00c2\u00a0communicates any change in the emulation of FS-UAE’s Amiga parallel port to an\u00c2\u00a0external process and also receives external changes for input lines from the\u00c2\u00a0process and realizes them in FS-UAE’s emulated parallel port.<\/p>\n

Having a POSIX compatible system with pseudo-terminals (ptys) I devised the\u00c2\u00a0link between both processes as a simple file-open interface in FS-UAE and a pty\u00c2\u00a0in the plipbox emulator (Note: any other interprocess mechanism works here also\u00c2\u00a0but this one was very easy to add in FS-UAE).<\/p>\n

The setup looks like this:<\/p>\n

        +----------+                                  +---------+\r\n        | plipbox  |                                  | patched |\r\n        | emulator |--(opens)--> [PTY] <--(file I\/O)--| FS-UAE  |\r\n        +----------+                                  +---------+\r\n                    <--------- vpar protocol --------><\/pre>\n
All required changes to FS-UAE are available in my clone of the FS-UAE\u00c2\u00a0repository on GitHub<\/a> in the `chris-devel` branch.<\/p>\n
For the plipbox emulator application I chose my favorite script language\u00c2\u00a0Python. With it setting up the pty for inter-process communication and\u00c2\u00a0implementing the vpar protocol peer was done in a few hours.<\/p>\n
Setting up the Network<\/h3>\n
Ok, the plipbox emulator in Python can now talk PLIP via vpar’s virtual\u00c2\u00a0parallel port. The next step is to add access to an Ethernet device on the\u00c2\u00a0lowest frame level for our plipbox emulator.<\/p>\n
I had a look at the pcap<\/a> library that allows injecting packets into\u00c2\u00a0an existing adapter, but the Python bindings often lacked the inject feature\u00c2\u00a0of the library and so I dropped this idea.<\/p>\n
Then I found a setup using a TAP<\/a> device to easily create and receive\u00c2\u00a0ethernet packets from a user space application. Combine this with a real\u00c2\u00a0ethernet adapter via an interface bridge and you have access to real ethernet\u00c2\u00a0with a simple TAP file I\/O interface (opening \/dev\/tap0) from your\u00c2\u00a0application.<\/p>\n
The setup looks like this:<\/p>\n
        +----------+              +---------+                +----------+\r\n        | Real Eth |              | TAP     |                | plipbox  |\r\n        | Adapter  |<-- Bridge -->| Adapter |<-- File I\/O -->| emulator |\r\n        +----------+              +---------+                +----------+\r\n           en1         bridge0       tap0\r\n           +----- OS net interfaces ----+<\/pre>\n
For the real ethernet adapter I use a second USB ethernet adapter on my Mac\u00c2\u00a0that is not configured (IP: 0.0.0.0) but active (up) in Mac OS X. This way OS X\u00c2\u00a0does not use it and my emulator can use it exclusively.<\/p>\n
Creating the TAP device and building the bridge with the real adapter is done\u00c2\u00a0with some sudo’ed system command right in the startup of the emulator.<\/p>\n
Note: the TAP driver is not shipped with Mac OS X itself, but you can add it by\u00c2\u00a0installing the ones from the TUN TAP OSX<\/a> project.<\/p>\n
Putting it all together<\/h3>\n
On top of the vpar Python module I implemented the magPLIP protocol layer in\u00c2\u00a0an own Python class. Now all pieces to create the plipbox were available.<\/p>\n
The plipbox main script sets up the vpar, magplip, and ethernet with TAP and\u00c2\u00a0interface bridge. In the main loop it does I\/O multi-plexing with select() on\u00c2\u00a0the file descriptor for the vpar PTY and for the TAP file.<\/p>\n
A packet arriving from TAP is filtered (i.e. multicast and unknown broadcasts\u00c2\u00a0are removed) similar to the real plipbox firmware and then delivered to the\u00c2\u00a0emulated Amiga via the vpar connection.<\/p>\n
A packet incoming via PLIP is directly delivered to the local network and thus\u00c2\u00a0written to the TAP file.<\/p>\n
That’s it! A working plipbox running as a Python script on my Mac…\u00c2\u00a0Similar to the firmware I added some optional debugging output to see the\u00c2\u00a0packet contents and to measure the timing and latency. Now I can develop and test the plipbox.device driver with the emulated environment…<\/p>\n
Sneak a Peek?<\/h3>\n
The plipbox emulator will be shipped with the upcoming version 0.3 of plipbox. If you want to have a look already then head over to my GitHub<\/a> repository where all development takes place… Have a look in the python<\/strong> and doc<\/strong> dirs \ud83d\ude42<\/p>\n
 <\/p>\n","protected":false},"excerpt":{"rendered":"
Recently, I had some time to spend and wanted to work on the plipbox project’s Amiga driver. Unfortunately, I only had my MacBook Pro with me and no\u00c2\u00a0Amiga or plipbox hardware. What does a SW developer do if the real … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"ngg_post_thumbnail":0,"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[11,6,15,9],"tags":[],"class_list":["post-628","post","type-post","status-publish","format-standard","hentry","category-amiga","category-mac-stuff","category-plipbox","category-software"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/piBMF-a8","jetpack_sharing_enabled":true,"jetpack_likes_enabled":true,"jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/lallafa.de\/blog\/wp-json\/wp\/v2\/posts\/628","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/lallafa.de\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/lallafa.de\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/lallafa.de\/blog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/lallafa.de\/blog\/wp-json\/wp\/v2\/comments?post=628"}],"version-history":[{"count":2,"href":"https:\/\/lallafa.de\/blog\/wp-json\/wp\/v2\/posts\/628\/revisions"}],"predecessor-version":[{"id":630,"href":"https:\/\/lallafa.de\/blog\/wp-json\/wp\/v2\/posts\/628\/revisions\/630"}],"wp:attachment":[{"href":"https:\/\/lallafa.de\/blog\/wp-json\/wp\/v2\/media?parent=628"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/lallafa.de\/blog\/wp-json\/wp\/v2\/categories?post=628"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/lallafa.de\/blog\/wp-json\/wp\/v2\/tags?post=628"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}