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@ -1,11 +1,16 @@
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# basic
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This is a BASIC interpreter which has been written from scratch for Collapse OS.
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**Work in progress, not finished.**
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This is a BASIC interpreter which is being written from scratch for Collapse OS.
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There are many existing z80 implementations around, some of them open source
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and most of them good and efficient, but because a lot of that code overlaps
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with code that has already been written for zasm, I believe that it's better to
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reuse those bits of code.
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Integrating an existing BASIC to Collapse OS seemed a bigger challenge than
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writing from scratch, so here I am, writing from scratch again...
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## Design goal
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The reason for including a BASIC dialect in Collapse OS is to supply some form
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@ -93,17 +98,17 @@ with variables in it, work fine.
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There are two types of commands: normal and direct-only. The latter can only
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be invoked in direct mode, not through a code listing.
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`bye`: Direct-only. Quits BASIC
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**bye**: Direct-only. Quits BASIC
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`list`: Direct-only. Prints all lines in the code listing, prefixing them
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**list**: Direct-only. Prints all lines in the code listing, prefixing them
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with their associated line number.
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`run`: Direct-only. Runs code from the listing, starting with the first one.
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**run**: Direct-only. Runs code from the listing, starting with the first one.
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If `goto` was previously called in direct mode, we start from that line instead.
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`clear`: Direct-only. Clears the current code listing.
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**clear**: Direct-only. Clears the current code listing.
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`print <what> [<what>]`: Prints the result of the specified expression,
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**print <what> [<what>]**: Prints the result of the specified expression,
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then CR/LF. Can be given multiple arguments. In that case, all arguments are
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printed separately with a space in between. For example, `print 12 13` prints
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`12 13<cr><lf>`
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@ -112,48 +117,48 @@ Unlike anywhere else, the `print` command can take a string inside a double
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quote. That string will be printed as-is. For example, `print "foo" 40+2` will
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print `foo 42`.
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`goto <lineno>`: Make the next line to be executed the line number
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**goto <lineno>**: Make the next line to be executed the line number
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specified as an argument. Errors out if line doesn't exist. Argument can be
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an expression. If invoked in direct mode, `run` must be called to actually
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run the line (followed by the next, and so on).
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`if <cond> <cmd>`: If specified condition is true, execute the rest of the
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**if <cond> <cmd>**: If specified condition is true, execute the rest of the
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line. Otherwise, do nothing. For example, `if 2>1 print 12` prints `12` and `if
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2<1 print 12` does nothing. The argument for this command is a "thruth
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expression".
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`input [<prompt>]`: Prompts the user for a numerical value and puts that
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**input [<prompt>]**: Prompts the user for a numerical value and puts that
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value in `A`. The prompted value is evaluated as an expression and then stored.
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The command takes an optional string literal parameter. If present, that string
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will be printed before asking for input. Unlike a `print` call, there is no
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CR/LF after that print.
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`peek/deek <addr>`: Put the value at specified memory address into `A`. peek is for
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**peek/deek <addr>**: Put the value at specified memory address into `A`. peek is for
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a single byte, deek is for a word (little endian). For example, `peek 42` puts
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the byte value contained in memory address 0x002a into variable `A`. `deek 42`
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does the same as peek, but also puts the value of 0x002b into `A`'s MSB.
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`poke/doke <addr> <val>`: Put the value of specified expression into
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**poke/doke <addr> <val>**: Put the value of specified expression into
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specified memory address. For example, `poke 42 0x102+0x40` puts `0x42` in
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memory address 0x2a (MSB is ignored) and `doke 42 0x102+0x40` does the same
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as poke, but also puts `0x01` in memory address 0x2b.
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`in <port>`: Same thing as `peek`, but for a I/O port. `in 42` generates an
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**in <port>**: Same thing as `peek`, but for a I/O port. `in 42` generates an
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input I/O on port 42 and stores the byte result in `A`.
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`out <port> <val>`: Same thing as `poke`, but for a I/O port. `out 42 1+2`
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**out <port> <val>**: Same thing as `poke`, but for a I/O port. `out 42 1+2`
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generates an output I/O on port 42 with value 3.
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`getc`: Waits for a single character to be typed in the console and then puts
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**getc**: Waits for a single character to be typed in the console and then puts
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that value in `A`.
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`putc <char>`: Puts the specified character to the console.
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**putc <char>**: Puts the specified character to the console.
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`sleep <units>`: Sleep a number of "units" specified by the supplied
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**sleep <units>**: Sleep a number of "units" specified by the supplied
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expression. A "unit" depends on the CPU clock speed. At 4MHz, it is roughly 8
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microseconds.
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`addr <what>`: This very handy returns (in `A`), the address you query for.
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**addr <what>**: This very handy returns (in `A`), the address you query for.
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You can query for two types of things: commands or special stuff.
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If you query for a command, type the name of the command as an argument. The
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@ -163,7 +168,7 @@ Then, there's the *special stuff*. This is the list of things you can query for:
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* `$`: the scratchpad.
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`usr <addr>`: This calls the memory address specified as an expression
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**usr <addr>**: This calls the memory address specified as an expression
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argument. Before doing so, it sets the registers according to a specific
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logic: Variable `A`'s LSB goes in register `A`, variable `D` goes in register
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`DE`, `H` in `HL` `B` in `BC` and `X` in `IX`. `IY` can't be used because
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@ -186,24 +191,24 @@ Here's the documentation for them.
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Block devices commands. Block devices are configured during kernel
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initialization and are referred to by numbers.
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`bsel <blkid>`: Select the active block device. The active block device is
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**bsel <blkid>**: Select the active block device. The active block device is
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the target of all commands below. You select it by specifying its number. For
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example, `bsel 0` selects the first configured device. `bsel 1` selects the
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second.
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A freshly selected blkdev begins with its "pointer" at 0.
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`seek <lsw> <msw>`: Moves the blkdev "pointer" to the specified offset. The
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**seek <lsw> <msw>**: Moves the blkdev "pointer" to the specified offset. The
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first argument is the offset's least significant half (blkdev supports 32-bit
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addressing). Is is interpreted as an unsigned integer.
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The second argument is optional and is the most significant half of the address.
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It defaults to 0.
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`getb`: Read a byte in active blkdev at current pointer, then advance the
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**getb**: Read a byte in active blkdev at current pointer, then advance the
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pointer by one. Read byte goes in `A`.
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`putb <val>`: Writes a byte in active blkdev at current pointer, then
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**putb <val>**: Writes a byte in active blkdev at current pointer, then
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advance the pointer by one. The value of the byte is determined by the
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expression supplied as an argument. Example: `putb 42`.
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@ -211,9 +216,9 @@ expression supplied as an argument. Example: `putb 42`.
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`fs.asm` provides those commands:
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`fls`: prints the list of files contained in the active filesystem.
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**fls**: prints the list of files contained in the active filesystem.
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`fopen <fhandle> <fname>`: Open file "fname" in handle "fhandle". File handles
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**fopen <fhandle> <fname>**: Open file "fname" in handle "fhandle". File handles
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are specified in kernel glue code and are in limited number. The kernel glue
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code also maps to blkids through the glue code. So to know what you're doing
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here, you have to look at your glue code.
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@ -224,16 +229,16 @@ handle 1 maps to blkid 2.
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Once a file is opened, you can use the mapped blkid as you would with any block
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device (bseek, getb, putb).
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`fnew <blkcnt> <fname>`: Allocates space of "blkcnt" blocks (each block is
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**fnew <blkcnt> <fname>**: Allocates space of "blkcnt" blocks (each block is
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0x100 bytes in size) for a new file names "fname". Maximum blkcnt is 0xff.
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`fdel <fname>`: Mark file named "fname" as deleted.
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**fdel <fname>**: Mark file named "fname" as deleted.
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`ldbas <fname>`: loads the content of the file specified in the argument
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**ldbas <fname>**: loads the content of the file specified in the argument
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(as an unquoted filename) and replace the current code listing with this
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contents. Any line not starting with a number is ignored (not an error).
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`basPgmHook`: That is not a command, but a routine to hook into
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**basPgmHook**: That is not a command, but a routine to hook into
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`BAS_FINDHOOK`. If you do, whenever a command name isn't found, the filesystem
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is iterated to see if it finds a file with the same name. If it does, it loads
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its contents at `USER_CODE` (from `user.h`) and calls that address, with HL
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