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recipes/trs80: new recipe (WIP)
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recipes/trs80/README.md
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recipes/trs80/README.md
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# TRS-80 Model 4p
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The TRS-80 (models 1, 3 and 4) are among the most popular z80 machines. They're
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very nicely designed and I got my hands on a 4p with two floppy disk drives and
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a RS-232 port. In this recipe, we're going to get Collapse OS running on it.
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**This is a work in progress. Collapse OS doesn't run on it yet.**
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## Floppy or RS-232?
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There are many ways to get Collapse OS to run on it. One would involve writing
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it to a floppy. I bought myself old floppy drives for that purpose, but I happen
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to not have any functional computer with a floppy port on it. I still have the
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motherboard of my old pentium, but I don't seem to have a video card for it any
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more.
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Because my 4p has a RS-232 port and because I have equipment to do serial
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communication from modern machines (I didn't have a DB-9 to DB-25 adapter
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though, I had to buy one), I chose that route.
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## Gathering parts
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* A TRS-80 model 4p with a RS-232 port
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* A TRSDOS 6.x disk
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* A means to do serial communication. In my case, that meant:
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* A USB-to-serial device
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* A null modem cable
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* A DB-9 gender changer
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* A DB-9 to DB-25 adapter
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## Overview
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We need to send sizeable binary programs through the RS-232 port and then run
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it. The big challenge here is ensuring data integrity. Sure, serial
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communication has parity check, but it has no helpful way of dealing with
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parity errors. When parity check is enabled and that a parity error occurs, the
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byte is simply dropped on the receiving side. Also, a double bit error could be
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missed by those checks.
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What we'll do here is to ping back every received byte back and have the sender
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do the comparison and report mismatched data.
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Another problem is ASCII control characters. When those are sent across serial
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communication channels, all hell breaks lose. When sending binary data, those
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characters have to be avoided. We use `tools/ttysafe` for that.
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Does TRSDOS have a way to receive this binary inside these constraints? Not to
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my knowledge. As far as I know, the COMM program doesn't allow this.
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What are we going to do? We're going to punch in a binary program to handle that
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kind of reception! You're gonna feel real badass about it too...
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## Testing serial communication
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The first step here is ensuring that you have bi-directional serial
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communication. To do this, first prepare your TRS-80:
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set *cl to com
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setcomm (word=8, parity=no)
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The first line loads the communication driver from the `COM/DRV` file on the
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TRSDOS disk and binds it to `*cl`, the name generally used for serial
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communication devices. The second line sets communication parameters in line
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with what is generally the default on modern machine. Note that I left the
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default of 300 bauds as-is.
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Then, you can run `COMM *cl` to start a serial communication console.
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Then, on the modern side, use your favorite serial communication program and set
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the tty to 300 baud with option "raw". Make sure you have `-parenb`.
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If your line is good, then what you type on either side should echo on the
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other side. If it does not, something's wrong. Debug.
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## Punching in the goodie
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As stated in the overview, we need a program on the TRS-80 that:
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1. Listens to `*cl`
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2. Echoes each character back to `*cl`
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3. Adjusts `ttysafe` escapes
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4. Stores received bytes in memory
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That program has already been written, it's in `recv.asm` in this folder. You
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can get the binary with `zasm < recv.asm | xxd`.
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How will you punch that in? The `debug` program! This very useful piece of
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software is supplied in TRSDOS. To invoke it, first run `debug (on)` and then
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press the `BREAK` key. You'll get the debug interface which allows you to punch
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in any data in any memory address. Let's use `0x3000` which is the offset for
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user apps.
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First, display the `0x3000-0x303f` range with the `d3000<space>` command (I
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always press Enter by mistake, but it's space you need to press). Then, you can
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begin punching in with `h3000<space>`. This will bring up a visual indicator of
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the address being edited. Punch in the stuff with a space in between each byte
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and end the edit session with `x`.
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But wait, it's not that easy! You see those `0xffff` addresses? They're
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placeholders. You need to replace those values with your DCB handle for `*cl`.
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See below.
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## Getting your DCB address
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In the previous step, you need to replace the `0xffff` placeholders in
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`recv.asm` with your "DCB" address for `*cl`. That address is your driver
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"handle". To get it, first get the address where the driver is loaded in
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memory. You can get this by running `device (b=y)`. That address you see next
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to `*cl`? that's it. But that's not our DCB.
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To get your DBC, go explore that memory area. Right after the part where there's
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the `*cl` string, there's the DCB address (little endian). On my setup, the
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driver was loaded in `0x0ff4` and the DCB address was 8 bytes after that, with
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a value of `0x0238`.
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## Sending data through the RS-232 port
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Once you're finished punching your program in memory, you can run it with
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`g3000<enter>` (not space). Because it's an infinite loop, your screen will
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freeze. You can start sending your data.
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To that end, there's the `tools/pingpong` program. It takes a device and a
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filename to send. As a test, send anything, but make it go through
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`tools/ttysafe` first (which just takes input from stdin and spits tty-safe
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content to stdout).
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On OpenBSD, the invocation can look like:
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doas ./pingpong /dev/ttyU0 mystuff.ttysafe
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You will be prompted for a key before the contents is sent. This is because on
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OpenBSD, TTY configuration is lost as soon as the TTY is closed, which means
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that you can't just run `stty` before running `pingpong`. So, what you'll do is,
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before you press your key, run `doas stty -f /dev/ttyU0 300 raw` and then press
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any key on the `pingpong` invocation.
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If everything goes well, the program will send your contents, verifying every
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byte echoed back, and then send a null char to indicate to the receiving end
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that it's finished sending. This will end the infinite loop on the TRS-80 side
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and return. That should bring you back to a refreshed debug display and you
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should see your sent content in memory, at the specified address (`0x3040` if
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you didn't change it).
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**WIP: that's where we are for now...**
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36
recipes/trs80/recv.asm
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recipes/trs80/recv.asm
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ld hl, 0x3040 ; memory address where to put contents.
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loop:
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ld a, 0x03 ; @GET
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ld de, 0xffff ; replace with *CL's DCB addr
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rst 0x28
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jr nz, maybeerror
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or a
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ret z ; Sending a straight NULL ends the comm.
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; @PUT that char back
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ld c, a
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ld a, 0x04 ; @PUT
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ld de, 0xffff ; replace with *CL's DCB addr
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rst 0x28
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jr nz, error
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ld a, c
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cp 0x20
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jr z, adjust
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write:
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ld (hl), a
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inc hl
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jr loop
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adjust:
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dec hl
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ld a, (hl)
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and 0x7f
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jr write
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maybeerror:
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; was it an error?
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or a
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jr z, loop ; not an error, just loop
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; error
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error:
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ld c, a ; Error code from @GET/@PUT
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ld a, 0x1a ; @ERROR
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rst 0x28
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ret
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2
tools/.gitignore
vendored
2
tools/.gitignore
vendored
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/blkdump
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/blkdump
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/upload
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/upload
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/fontcompile
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/fontcompile
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/ttysafe
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/pingpong
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@ -2,7 +2,10 @@ MEMDUMP_TGT = memdump
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BLKDUMP_TGT = blkdump
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BLKDUMP_TGT = blkdump
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UPLOAD_TGT = upload
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UPLOAD_TGT = upload
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FONTCOMPILE_TGT = fontcompile
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FONTCOMPILE_TGT = fontcompile
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TARGETS = $(MEMDUMP_TGT) $(BLKDUMP_TGT) $(UPLOAD_TGT) $(FONTCOMPILE_TGT)
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TTYSAFE_TGT = ttysafe
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PINGPONG_TGT = pingpong
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TARGETS = $(MEMDUMP_TGT) $(BLKDUMP_TGT) $(UPLOAD_TGT) $(FONTCOMPILE_TGT) \
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$(TTYSAFE_TGT) $(PINGPONG_TGT)
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OBJS = common.o
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OBJS = common.o
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all: $(TARGETS)
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all: $(TARGETS)
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56
tools/pingpong.c
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tools/pingpong.c
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#include <stdlib.h>
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#include <stdio.h>
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#include <fcntl.h>
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#include <unistd.h>
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#include "common.h"
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/* Sends the contents of `fname` to `device`, expecting every sent byte to be
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* echoed back verbatim. Compare every echoed byte with the one sent and bail
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* out if a mismatch is detected. When the whole file is sent, push a null char
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* to indicate EOF to the receiving end.
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*
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* It is recommended that you send contents that has gone through `ttysafe`.
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*/
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int main(int argc, char **argv)
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{
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if (argc != 3) {
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fprintf(stderr, "Usage: ./pingpong device fname\n");
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return 1;
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}
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FILE *fp = fopen(argv[2], "r");
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if (!fp) {
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fprintf(stderr, "Can't open %s.\n", argv[2]);
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return 1;
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}
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int fd = open(argv[1], O_RDWR|O_NOCTTY|O_NONBLOCK);
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printf("Press a key...\n");
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getchar();
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unsigned char c;
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// empty the recv buffer
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while (read(fd, &c, 1) == 1) usleep(1000);
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int returncode = 0;
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while (fread(&c, 1, 1, fp)) {
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putchar('.');
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fflush(stdout);
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write(fd, &c, 1);
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usleep(1000); // let it breathe
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unsigned char c2;
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while (read(fd, &c2, 1) != 1); // read echo
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if (c != c2) {
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// mismatch!
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unsigned int pos = ftell(fp);
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fprintf(stderr, "Mismatch at byte %d! %d != %d.\n", pos, c, c2);
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returncode = 1;
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break;
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}
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}
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// To close the receiving loop on the other side, we send a straight null
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c = 0;
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write(fd, &c, 1);
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printf("Done!\n");
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fclose(fp);
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return returncode;
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}
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tools/ttysafe.c
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#include <stdlib.h>
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#include <stdio.h>
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/* Converts stdin to a content that is "tty safe", that is, that it doesn't
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* contain ASCII control characters that can mess up serial communication.
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* How it works is that it leaves any char > 0x20 intact, but any char <= 0x20
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* is replaced by two chars: char|0x80, 0x20. A 0x20 char always indicate "take
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* the char you've just received and unset the 7th bit from it".
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*/
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int main(void)
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{
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int c = getchar();
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while (c != EOF) {
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if (c <= 0x20) {
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putchar(c|0x80);
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putchar(0x20);
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} else {
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putchar(c&0xff);
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}
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c = getchar();
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}
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return 0;
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}
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