197 lines
5.3 KiB
Text
197 lines
5.3 KiB
Text
# I/O Devices
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I/O devices on Nga are exposed via three instructions:
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ie enumerate i/o devices
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iq query i/o device for class and version
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ii invoke i/o interaction
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All devices are registered with the VM. How this occurs is
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implementation dependent.
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## Counting Devices
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Use the `ie` instruction to return the number of attached devices.
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i ie......
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Upon running, the stack will contain the number of devices. You
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can then query these by passing the device number to `iq`.
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## Query Devices
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Use `iq` to query an attached device. This will return two values,
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a device class and a revision number.
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The device class will be the top value on the stack.
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## Invoking a Device
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You can trigger an I/O operation by passing the device handle to
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the `ii` instruction.
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E.g., to display a character (ASCII code 98 in this case):
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i liliii..
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d 98
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d 0
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Be sure to pass the device handle, not the device class.
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## Device Class
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Ultimately devices are implementation-specific, but the
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standard system provides or reserves the following:
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ID | Device Class | Notes |
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-----+------------------+----------------------------+
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0000 | Generic Output | Always present as handle 0 |
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0001 | Keyboard | |
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0002 | Floating Point | |
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0003 | Block Storage | Raw, 1024 cell blocks |
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0004 | Filesystem | Unix-style Files |
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0005 | Clock | |
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0006 | | |
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0007 | Network: Sockets | |
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0008 | Syscalls: Unix | |
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0009 | Scripting Hooks | |
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0010 | Random Number | |
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1000 | Image Saving | |
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It must be noted here that nothing forces devices to use these
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class identifiers, and one must take care to use an Nga
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implementation that provides the devices they need.
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## Device Revisions
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Over time, the functionality a device provides may change. To allow
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detection of this, the query functionality provides a revision number.
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Your code can use this to ensure that the device provided supports
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the level of functionality you need.
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## Device Class Details
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### 0000: Generic Output
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Supported by all Nga implementations. This is required to be the
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first device, and is the only one guaranteed to be provided. It
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consumes a value from the stack, writing to to the host-specific
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output. (This does not need to be a screen).
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### 0001: Keyboard
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Read and return a keypress.
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Consumes no data, returns a single value representing the
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character that was read.
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No subcommands are defined.
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### 0002: Floating Point
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The current revision is 1.
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It currently provides:
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n:to-float (n-_f:-n)
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s:to-float (s-_f:-n)
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f:to-number (f:a-__-n)
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f:to-string (f:n-__-s)
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f:+ (f:ab-c)
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f:- (f:ab-c)
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f:* (f:ab-c)
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f:/ (f:ab-c)
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f:floor (f:ab-c)
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f:ceiling (f:f-f)
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f:sqrt (f:f-f)
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f:eq? (f:ab-c)
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f:-eq? (f:ab-c)
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f:lt? (f:ab-c)
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f:gt? (f:ab-c)
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f:depth (-n)
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f:dup (f:a-aa)
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f:drop (f:a-)
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f:swap (f:ab-ba)
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f:log (f:ab-c)
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f:power (f:ab-c)
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f:sin (f:f-f)
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f:cos (f:f-f)
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f:tan (f:f-f)
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f:asin (f:f-f)
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f:acos (f:f-f)
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f:atan (f:f-f)
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f:push (f:f-)
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f:pop (f:-f)
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f:adepth (-n)
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### 0003: Block Storage
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Reserved for future use.
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### 0004: Filesystem
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Currently at revision 0.
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This implements a device providing traditional Unix-like files.
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Takes a value indicating an operation, and each operation takes
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additional values.
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| Operation | Stack | Action |
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| --------- | ----- | -------------------------------- |
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| 0 | sm-h | Open a file |
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| 1 | h- | Close a file |
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| 2 | h-c | Read a byte from a file |
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| 3 | ch- | Write a byte to a file |
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| 4 | h-n | Return current pointer into file |
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| 5 | nh- | Move pointer in a file |
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| 6 | h-n | Return the size of a file |
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| 7 | s- | Delete a file |
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| 8 | h- | Flush pending writes |
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### 0010: Random Number Generator
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This is currently at revision 0.
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On invocation, this returns a random number.
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## Implementation Details (C)
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On the C implementation, each I/O device has the needed support
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functions defined, then a query function and invocation function
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defined.
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As an example, to add a device that has two functions, I might do:
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void one() {
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stack_push(100);
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}
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void two() {
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stack_push(200);
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}
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Handler device_actions[] = {
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one, two
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}
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void io_device() {
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device_actions[stack_pop()]();
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}
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void query_device() {
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stack_push(0); /* Revision */
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stack_push(1234); /* Device Class */
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}
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Then add pointers to `io_device` to `IO_deviceHandlers` and
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`query_device` to `IO_queryHandlers` and increase the `NUM_DEVICES`
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by one.
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You will then need to write a set of Retro words to use the new
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device.
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:device:one #1 #1234 io:scan-for io:invoke ;
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:device:two #2 #1234 io:scan-for io:invoke ;
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Rebuild the VM, adding these to image.
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