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@ -210,3 +210,34 @@ always successful.
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66 BANK B=func C=bank BZ Memory bank use
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67 BREAK HL=vector HL Set Break vector
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68 SOUND B=func - Sound generation
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## Personal reverse engineering
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This section below contains notes about my personal reverse engineering efforts.
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I'm not an expert in this, and also, I might not be aware of existing, better
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documentation making this information useless.
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### Bootable disk
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I'm wondering what makes a disk bootable to the TRS-80 and how it boots it.
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When I read the raw contents of the first sector of the first cylinder of the
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TRS-DOS disk, I see that, except for the 3 first bytes (`00fe14`), the rest of
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the contents is exactly the same as what is at memory offset `0x0203`, which
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seems to indicates that the bootloader simply loads that contents to memory,
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leaving the first 3 bytes of RAM to either random contents or some predefined
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value (I have `f8f800`).
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A non-bootable disk starts with `00fe14`, but we can see the message "Cannot
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boot, DA TA DISK!" at offset `0x2a`.
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I'm not sure what `00fe14` can mean. Disassembled, it's
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`nop \ rst 0x28 \ ld b, c`. It makes sense that booting would start with a
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service call with parameters set by the bootloader (so we don't know what that
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service call actually is), but I'm not sure it's what happens.
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I don't see any reference to the `0x2a` offset in the data from the first
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sector, but anyways, booting with the non-bootable disk doesn't actually prints
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the aformentioned message, so it might be a wild goose chase.
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In any case, making a disk bootable isn't a concern as long as Collapse OS uses
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the TRS-DOS drivers.
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@ -76,6 +76,9 @@ printnstr:
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pop bc
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ret
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; Prints a line terminator. This routine is a bit of a misnomer because it's
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; designed to be overridable to, for example, printlf, but we'll live with it
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; for now...
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printcrlf:
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push af
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ld a, CR
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@ -151,6 +151,10 @@ A memory range dumped this way will be re-loaded at the same offset through
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using the `RUN` command. Therefore, you can avoid all this work above in later
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sessions by simply typing `recv` in the DOS prompt.
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Note that you might want to turn `debug` off for these commands to run. I'm not
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sure why, but when the debugger is on, launching the command triggers the
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debugger.
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## Sending binary 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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@ -186,6 +190,12 @@ If there was no error during `pingpong`, the content should be exact.
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Nevertheless, I recommend that you manually validate a few bytes using TRSDOS
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debugger before carrying on.
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*debugging tip*: Sometimes, the communication channel can be a bit stubborn and
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always fail, as if some leftover data was consistently blocking the channel. It
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would cause a data mismatch at the very beginning of the process, all the time.
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What I do in these cases is start a `COMM *cl` session on one side and a screen
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session on the other, type a few characters, and try `pingpong` again.
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## Running Collapse OS
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If everything went well, you can run Collapse OS with `g3000<space>`. You'll
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@ -18,6 +18,9 @@
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.equ STDIO_PUTC trs80PutC
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.inc "stdio.asm"
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; The TRS-80 generates a double line feed if we give it both CR and LF.
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.equ printcrlf printcr
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; *** BASIC ***
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; RAM space used in different routines for short term processing.
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@ -44,4 +47,11 @@ init:
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call basInit
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jp basStart
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printcr:
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push af
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ld a, CR
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call STDIO_PUTC
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pop af
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ret
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RAMSTART:
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