What is the MOS API
The MOS API can be used by external applications to access MOS functionality.
Please note that this documentation uses assembler in the examples in a format that is compatible with the Zilog ZDS II assembler. The assembler syntax used in BBC BASIC is similar, but not identical. Additionally you will need to use the new ADL version of BBC BASIC to use the new eZ80 ADL mode and extended instruction set.
This documentation is not intended as a tutorial on eZ80 assembler, but as a reference for those who are already familiar with the eZ80 or Z80 instruction set and wish to use MOS APIs in their programs.
Usage from Z80 assembler
There are four RST instructions for accessing MOS functionality from Z80.
RST 00h: Reset the eZ80RST 08h: Execute a MOS commandRST 10h: Output a single character to the VDPRST 18h: Output a stream of characters to the VDP (MOS 1.03 or above)RST 38h: Outputs a crash report (Console8 MOS 2.3.0 or above)
In addition, if you are using the Zilog ZDS II assembler you may wish to include the file mos_api.inc in your project. The Console8 version can be found in the folder src of project agon-mos. The original Quark versions of this file can be found in the folder src of project agon-mos.
NB:
- Using the
RST.LISopcode in an eZ80 assembler will ensure the MOS RST instructions are called regardless of the eZ80s current addressing mode. - In the
mos_api.incfile you will find: - EQUs for all the MOS commands, data structures and system variables.
- An incomplete list of VDP control variables. For a full list, see the VDP documentation
- A complete list FatFS APIs, however these are not yet all implemented in MOS. Those that are implemented are documented below.
Further information on the RST handlers provided by MOS are as follows:
RST 08h: Execute a MOS command
Parameters:
A: MOS command number to execute
NB:
- There is a macro in
mos_api.incwith EQUs for all the MOS commands - Other MOS-command dependant parameters may be required
Macro:
;
; Macro for calling the API
; Parameters:
; - `F`unction: One of the function numbers listed above
;
MOSCALL: MACRO function
LD A, function
RST.LIS 08h
ENDMACRO
Example:
; OSRDCH: Read a character in from the ESP32 keyboard handler
;
OSRDCH: MOSCALL mos_getkey
OR A
JR Z, OSRDCH ; Loop until key is pressed
RET
RST 10h: Output a single character to the VDP
Parameters:
A: Character to output
Example:
; OSWRCH: Write a character out to the ESP32 VDU handler via the MOS
; A: Character to write
;
OSWRCH: RST.LIS 10h ; This calls a RST in the eZ80 address space
RET
RST 18h: Output a stream of characters to the VDP (MOS 1.03 or above)
Parameters:
HL(U): Address of the data stream (16-bit for Z80 mode, 24-bit for ADL mode)BC: Length of stream (or 0 if the stream is delimited)A: Stream delimiter (ifBC=0)
Returns:
A: Last character displayed (length mode) OR Delimiter (delimiter mode)BC: 0HL(U): Address of last character displayed + 1 (length mode) OR location of delimiter (delimiter mode)E: Value ofAupon entry
Example:
; Write a stream of characters to the VDP
; HLU: Address of buffer containing data - if in 16-bit segment, U will be replaced by MB
; BC: Number of characters to write out, or 0 if the data is delimited
; A: End of data delimiter, i.e. 0 for C strings
;
LD HL, text ; Address of text
LD BC, 0 ; Set to 0, so length ignored...
LD A, 0 ; Use character in A as delimiter
RST.LIS 18h ; This calls a RST in the eZ80 address space
RET
;
text: DB "Hello World", 0
RST 38h: Outputs a crash report (Console8 MOS 2.3.0 or above)
This command will output a crash report to the screen. This report will show the current processor state, and the top of the stack. This can be useful for debugging purposes.
This command works in conjunction with the fact that as of Console8 MOS 2.3.0, on initial startup memory will be reset to contain 0xFF bytes in every location, which equates to a RST 38h instruction. This means that for many system crashes execution will end up at the RST 38h instruction, and a crash report will be displayed on the screen.
The MOS API
MOS API calls can be executed from a classic 64K Z80 segment or whilst the eZ80 is running in 24-bit ADL mode. For classic mode, 16 bit registers are passed as pointers to the MOS commands; these are automatically promoted to 24 bit by adding the MB register to bits 16-23 of the register. When running in ADL mode, a 24-bit register will be passed, but MB must be set to 0.
The following MOS commands are supported:
0x00: mos_getkey
Read a keypress from the VDP
Parameters: None
Returns:
A: The keycode of the character pressed
NB: This is a blocking function. This routine will wait and only return once a key is pressed.
0x01: mos_load
Load a file from SD card
Parameters:
- HL(U): Address of filename (zero terminated)
- DE(U): Address at which to load
- BC(U): Maximum allowed size (bytes)
Preserves: HL(U), DE(U), BC(U)
Returns:
A: File error, or 0 if OKF: Carry reset if no room for file, otherwise set
0x02: mos_save
Save a file to SD card
Parameters:
HL(U): Address of filename (zero terminated)DE(U): Address to save fromBC(U): Number of bytes to save
Preserves: HL(U), DE(U), BC(U)
Returns:
A: File error, or 0 if OKF: Carry set
0x03: mos_cd
Change current directory on the SD card
Parameters:
HL(U): Address of path (zero terminated)
Preserves: HL(U)
Returns:
A: File error, or 0 if OK
0x04: mos_dir
List SD card folder contents to screen.
This is a simple directory listing command that will list the contents of the current directory to the screen. More advanced directory listing functionality for applications to use is available via the FatFS commands API.
Parameters:
HL(U): Address of path (zero terminated)
Preserves: HL(U)
Returns:
A: File error, or 0 if OK
0x05: mos_del
Delete a file or folder from the SD card
Parameters:
HL(U): Address of path (zero terminated)
Preserves: HL(U)
Returns:
A: File error, or 0 if OK
0x06: mos_ren
Rename a file on the SD card
Parameters:
HL(U): Address of filename1 (zero terminated)DE(U): Address of filename2 (zero terminated)
Preserves: HL(U), DE(U)
Returns:
A: File error, or 0 if OK
0x07: mos_mkdir
Make a folder on the SD card
Parameters:
HL(U): Address of path (zero terminated)
Preserves: HL(U)
Returns:
A: File error, or 0 if OK
0x08: mos_sysvars
Fetch a pointer to the system variables
Parameters: None
Returns:
IXU: Pointer to the MOS system variable area (this is always 24 bit)
0x09: mos_editline
Invoke the line editor
Parameters:
HL(U): Address of the bufferBC(U): Buffer lengthE: Flags to control editor behaviour
Preserves: HL(U), BC(U), DE(U)
Returns:
A: Key that was used to exit the input loop (CR=13, ESC=27)
Editor behaviour flags are as follows:
| Bit | Description |
|---|---|
| 0 | When set, buffer will be cleared before use |
| 1 | When set, tab-completion for MOS commands and files is enabled * |
| 2 | When set, hotkeys are disabled * |
| 3 | When set, input history will be disabled * |
| 4-7 | Reserved for future use (for future compatibility, ensure these are set to zero) |
* Support for editor control flags was added in Console8 MOS 2.2.0. Prior to this the only documented values for E were 0 and 1 to indicate whether the buffer should be cleared.
0x0A: mos_fopen
Get a file handle
Parameters:
HL(U): Address of filename (zero terminated)C: Mode
Preserves: HL(U), BC(U), DE(U), IX(U), IY(U)
Returns:
A: File handle, or 0 if couldn't open
Mode can be one of: fa_read, fa_write, fa_open_existing, fa_create_new, fa_create_always, fa_open_always or fa_open_append
NB: If you open the file using mos_fopen, you must close it using mos_fclose, not ffs_api_fclose
0x0B: mos_fclose
Close a file handle
Parameters:
C: File handle, or 0 to close all open files
Preserves: HL(U), BC(U), DE(U), IX(U), IY(U)
Returns:
A: Number of files still open
0x0C: mos_fgetc
Get a character from an open file
Parameters:
C: File handle
Preserves: HL(U), BC(U), DE(U), IX(U), IY(U)
Returns:
A: Character readF: C set if last character in file, otherwise NC (MOS 1.04 or greater)
0x0D: mos_fputc
Write a character to an open file
Parameters:
C: File handleB: Character to write
Preserves: HL(U), BC(U), DE(U), IX(U), IY(U)
Returns: None
0x0E: mos_feof
Check for end of file
Parameters:
C: File handle
Preserves: HL(U), BC(U), DE(U), IX(U), IY(U)
Returns:
A: 1 if at end of file, otherwise 0
0x0F: mos_getError
Copy an error string to a buffer
Parameters:
E: The error codeHL(U): Address of buffer to copy message intoBC(U): Size of buffer
Preserves: DE(U), HL(U), BC(U)
Returns: None
0x10: mos_oscli
Execute a MOS command
Parameters:
HL(U): Pointer the the MOS command string
Preserves: HL(U)
Returns:
A: MOS error code
NB previously documentation for this command was incorrect, as it documented additional parameters in DE(U) and BC(U). These registers are not currently used.
0x11: mos_copy
Copy a file on the SD card
Parameters:
HL(U): Address of filename1 (zero terminated)DE(U): Address of filename2 (zero terminated)
Preserves: HL(U), BC(U), DE(U), IX(U), IY(U)
Returns:
A: File error, or 0 if OK
NB: Requires MOS 1.03 or greater
0x12: mos_getrtc
Get a time string from the RTC (Requires MOS 1.03 or above)
Parameters:
HL(U): Pointer to a buffer to copy the string to (at least 32 bytes)
Preserves: HL(U)
Returns:
A: Length of time string
0x13: mos_setrtc
Set the RTC (Requires MOS 1.03 or above)
Parameters:
HL(U): Pointer to a 6-byte buffer with the time data in
+0: Year (offset from 1980, so 1989 is 9)
+1: Month (1 to 12)
+2: Day of Month (1 to 31)
+3: Hour (0 to 23)
+4: Minute (0 to 59)
+5: Second (0 to 59)
Preserves: HL(U)
Returns: None
0x14: mos_setintvector
Set an interrupt vector (Requires MOS 1.03 or above)
Parameters:
E: Interrupt vector number to setHLU: Address of new interrupt vector (24-bit pointer)
Preserves: HLU, DEU
Returns:
HL(U): Address of the previous interrupt vector (24-bit pointer)
0x15: mos_uopen
Open UART1 (Requires MOS 1.03 or above)
To handle the received interrupts, you will need to assign a handler to UART1's interrupt vector (0x1A).
Parameters:
IXU: Pointer to a UART struct
+0: Baud rate (24-bit, little endian)
+3: Data bits (5, 6, 7 or 8)
+4: Stop bits (1 or 2)
+5: Parity bits (0: None, 1: Odd, 3: Even)
+6: Flow control (0: None, 1: Hardware)
+7: Enabled interrupts
- Bit 0: Set to enable received data interrupt
- Bit 1: Set to enable transmit data interrupt
- Bit 2: Set to enable line status change interrupt
- Bit 3: Set to enable modem status change interrupt
- Bit 4: Set to enable transmit complete interrupt
Preserves: HL(U)
Returns:
A: Error code (always 0)
0x16: mos_uclose
Close UART1 (Requires MOS 1.03 or above)
0x17: mos_ugetc
Read a character from UART1 (Requires MOS 1.03 or above)
Returns:
A: The character readF: C if successful, NC if the UART is closed
NB: If UART1 is open, this is a blocking function which means this routine will wait and only return once a character is received.
0x18: mos_uputc
Write a character to UART1 (Requires MOS 1.03 or above)
Parameters:
C: The character to write
Returns:
F: C if successful, NC if the UART is closed
0x19: mos_getfil
Get a pointer to a FIL structure in MOS (Requires MOS 1.03 or above)
Parameters:
C: File handle
Preserves: BC(U)
Returns:
HLU: 24-bit pointer to a FIL structure (in MOS RAM)
0x1A: mos_fread
Read a block of data from a file (Requires MOS 1.03 or above)
Parameters:
C: File handleHLU: Pointer to a buffer to read the data intoDEU: Number of bytes to read
Preserves: HL(U), BC(U)
Returns:
DEU: Number of bytes read
0x1B: mos_fwrite
Write a block of data to a file (Requires MOS 1.03 or above)
Parameters:
C: File handleHLU: Pointer to a buffer that contains the data to writeDEU: Number of bytes to write out
Preserves: HL(U), BC(U)
Returns:
DEU: Number of bytes written
0x1C: mos_flseek
Move the read/write pointer in a file (Requires MOS 1.03 or above)
Parameters:
C: File handleHLU: Least significant 3 bytes of the offset from the start of the fileE: Most significant byte of the offset (set to 0 for files < 16MB)
Preserves: HL(U), BC(U), DE(U)
Returns:
A: FRESULT
0x1D: mos_setkbvector
Allows user programs to access VDP keyboard packets without overriding the entire uart0 interrupt handler. The user program registered, will be called during the uart0 interrupt handler, being passed the address of the full VDP keyboard packet. Normal MOS key handling is disabled when a user program is registered.
Parameters:
C: Address length in HL (0 = 24bit, 1 = 16bit). If 1 then set the top byte of HLU(callback address) to MB (for ADL=0 callers)HL(U): Callback address of user program to register, or 0 to clear any previously registered vector
Returns: Nothing upon registration. The user program can expect the full VDP packet address in DE(24-bit) upon entry.
example code that registers a custom handler.
0x1E: mos_getkbmap
Fetch a pointer to the virtual keyboard map (Requires MOS 1.04 RC2 or above)
Parameters: None
Returns:
IXU: Pointer to the keyboard bitmap (this is always 24 bit)
0x1F: mos_i2c_open
Open the I2C bus as Master (Requires MOS 1.04 RC3 or above)
Parameters:
C: Frequency ID (1: 57600, 2: 115200, 3: 230400)
Preserves: HL(U), BC(U), DE(U), IX(U), IY(U)
Returns: None
0x20: mos_i2c_close
Close the I2C bus (Requires MOS 1.04 RC3 or above)
Parameters: None
Preserves: HL(U), BC(U), DE(U), IX(U), IY(U)
Returns: None
0x21: mos_i2c_write
Write a block of bytes to the I2C bus (Requires MOS 1.04 RC3 or above)
Parameters:
C: I2C AddressB: Number of bytes to write (maximum 32)HL(U): Pointer to a buffer to read the bytes from
Preserves: HL(U), DE(U), IX(U), IY(U)
Returns:
A: Status0: OK1: No response from I2C slave2: Data NACK4: Bus arbitration lost8: Bus error
0x22: mos_i2c_read
Read a block of bytes from the I2C bus (Requires MOS 1.04 RC3 or above)
Parameters:
C: I2C AddressB: Number of bytes to read (maximum 32)HL(U): Pointer to a buffer to write the bytes to
Preserves: HL(U), DE(U), IX(U), IY(U)
Returns:
A: Status0: OK1: No response from I2C slave2: Data NACK4: Bus arbitration lost8: Bus error
FatFS commands
MOS makes use of FatFS to access the SD card. Some of FatFS's functionality is exposed via the MOS API. The exact API calls listed here may be expanded in later versions of MOS.
For more information on FatFS data structures and functions, see the FatFS documentation.
0x80: ffs_fopen
Open a file (Requires MOS 1.03 or above)
Parameters:
HL(U): Pointer to an empty FIL structureDE(U): Pointer to a C (zero-terminated) filename stringC: File open mode
Preserves: HL(U), DE(U), C
Returns:
A: FRESULT
Example:
LD HL, fil ; FIL buffer
LD DE, filename ; Filename (0 terminated)
LD C, fa_read ; Mode
MOSCALL ffs_fopen ; Open the file
LD DE, buffer ; Where to store the read file
LD BC, 256 ; Number of bytes to read
MOSCALL ffs_fread ; Read the data in
PUSH BC ; Preserve number of bytes read
MOSCALL ffs_fclose ; Close the file
POP BC ; BC: Number of bytes read
RET
filename: DB "example.txt", 0 ; The file to read
fil: DS FIL_SIZE ; FIL buffer (defined in mos_api.inc)
buffer: DS 256 ; Buffer for storing read data
0x81: ffs_fclose
Close a file (Requires MOS 1.03 or above)
Parameters:
HL(U): Pointer to a FIL structure
Preserves: HL(U)
Returns:
A: FRESULT
See ffs_fopen for an example
0x82: ffs_fread
Read from a file (Requires MOS 1.03 or above)
Parameters:
HL(U): Pointer to a FIL structureDE(U): Pointer to a buffer to store the data inBC(U): Number of bytes to read (typically the size of the buffer)
Preserves: HL(U), DE(U)
Returns:
BC(U): Number of bytes readA: FRESULT
See ffs_fopen for an example
0x83: ffs_fwrite
Write to a file (Requires MOS 1.03 or above)
Parameters:
HL(U): Pointer to a FIL structureDE(U): Pointer to a buffer to read the data fromBC(U): Number of bytes to write (typically the size of the buffer)
Preserves: HL(U), DE(U)
Returns:
BC(U): Number of bytes writtenA: FRESULT
Example:
LD HL, fil ; FIL buffer
LD DE, filename ; Filename (0 terminated)
LD C, fa_write | fa_create_always ; Mode
MOSCALL ffs_fopen ; Open the file
LD DE, buffer ; Location of data to write
LD BC, 256 ; Number of bytes to write
MOSCALL ffs_write ; Write the data
MOSCALL ffs_fclose ; Close the file
RET
filename: DB "example.txt", 0 ; The file to read
fil: DS FIL_SIZE ; FIL buffer (defined in mos_api.inc)
buffer: DS 256 ; Buffer containing data to write out
0x84: ffs_flseek
Move the read/write pointer in a file (Requires MOS 1.03 or above)
Parameters:
HL(U): Pointer to a FIL structureDE(U): Least significant 3 bytes of the offset from the start of the fileC: Most significant byte of the offset (set to 0 for files < 16MB)
Preserves: HL(U), DE(U), BC(U)
0x85: ffs_ftruncate
Truncate a file to the current file pointer offset (Requires Console8 MOS 2.3.0 or above)
To truncate to a specified size you will need to use ffs_flseek to move the file pointer to the desired location before calling ffs_ftruncate.
Parameters:
HL(U): Pointer to a FIL structure
Preserves: HL(U)
0x8E: ffs_feof
Detect end of file (Requires MOS 1.03 or above)
Parameters:
HL(U): Pointer to a FIL structure
Preserves: HL(U)
Returns:
A: 1 if at the end of the file, otherwise 0
0x91: ffs_dopen
Open a directory (Requires Console8 MOS 2.2.0 or above)
Parameters:
HL(U): Pointer to a blank DIR structureDE(U): Pointer to a C (zero-terminated) directory path string
Preserves: HL(U), DE(U)
Returns:
A: FRESULT
0x92: ffs_dclose
Close a directory (Requires Console8 MOS 2.2.0 or above)
Parameters:
HL(U): Pointer to a DIR structure
Preserves: HL(U)
Returns:
A: FRESULT
0x93: ffs_dread
Read next directory entry into a FILINFO data structure (Requires Console8 MOS 2.2.0 or above)
Parameters:
HL(U): Pointer to a DIR structureDE(U): Pointer to a FILINFO structure
Preserves: HL(U), DE(U)
Returns:
A: FRESULT
0x96: ffs_stat
Get file information (Requires MOS 1.03 or above)
Parameters:
HL(U): Pointer to a FILINFO structureDE(U): Pointer to a C (zero-terminated) filename string
Preserves: HL(U), DE(U)
Returns:
A: FRESULT
Example:
LD HL, filinfo ; FILINFO buffer
LD DE, filename ; Filename (0 terminated)
MOSCALL ffs_stat
RET
filename: DB "example.txt", 0 ; The file to read
filinfo: DS FILINFO_SIZE ; FILINFO buffer (defined in mos_api.inc)
0x9E: ffs_getcwd
Get the current working directory (Requires Console8 MOS 2.2.0 or above)
Parameters:
HL(U): Pointer to a buffer to store the directory path inBC(U): Maximum length of the buffer
Preserves: HL(U), BC(U)
Returns:
A: FRESULT
System Variables
The MOS API command mos_sysvars returns a pointer to the base of the MOS system variables area in IXU as a 24-bit pointer. The MOS system variables are often simply referred to as sysvars.
The following system variables are available in mos_api.inc:
; System variable indexes for api_sysvars
; Index into _sysvars in globals.asm
;
sysvar_time: EQU 00h ; 4: Clock timer in centiseconds (incremented by 2 every VBLANK)
sysvar_vpd_pflags: EQU 04h ; 1: Flags to indicate completion of VDP commands
sysvar_keyascii: EQU 05h ; 1: ASCII keycode, or 0 if no key is pressed
sysvar_keymods: EQU 06h ; 1: Keycode modifiers
sysvar_cursorX: EQU 07h ; 1: Cursor X position
sysvar_cursorY: EQU 08h ; 1: Cursor Y position
sysvar_scrchar: EQU 09h ; 1: Character read from screen
sysvar_scrpixel: EQU 0Ah ; 3: Pixel data read from screen (R,B,G)
sysvar_audioChannel: EQU 0Dh ; 1: Audio channel
sysvar_audioSuccess: EQU 0Eh ; 1: Audio channel note queued (0 = no, 1 = yes)
sysvar_scrWidth: EQU 0Fh ; 2: Screen width in pixels
sysvar_scrHeight: EQU 11h ; 2: Screen height in pixels
sysvar_scrCols: EQU 13h ; 1: Screen columns in characters
sysvar_scrRows: EQU 14h ; 1: Screen rows in characters
sysvar_scrColours: EQU 15h ; 1: Number of colours displayed
sysvar_scrpixelIndex: EQU 16h ; 1: Index of pixel data read from screen
sysvar_vkeycode: EQU 17h ; 1: Virtual key code from FabGL
sysvar_vkeydown EQU 18h ; 1: Virtual key state from FabGL (0=up, 1=down)
sysvar_vkeycount: EQU 19h ; 1: Incremented every time a key packet is received
sysvar_rtc: EQU 1Ah ; 8: Real time clock data
sysvar_keydelay: EQU 22h ; 2: Keyboard repeat delay
sysvar_keyrate: EQU 24h ; 2: Keyboard repeat rate
sysvar_keyled: EQU 26h ; 1: Keyboard LED status
sysvar_scrMode: EQU 27h ; 1: Screen mode (from MOS 1.04)
sysvar_rtc_enable: EQU 28h ; 1: RTC enable status (from Console8 MOS 2.0.0)
sysvar_mouseX: EQU 29h ; 2: Mouse X position
sysvar_mouseY: EQU 2Bh ; 2: Mouse Y position
sysvar_mouseButtons: EQU 2Dh ; 1: Mouse left+right+middle buttons (bits 0-2, 0=up, 1=down)
sysvar_mouseWheel: EQU 2Eh ; 1: Mouse wheel delta
sysvar_mouseXDelta: EQU 2Fh ; 2: Mouse X delta
sysvar_mouseYDelta: EQU 31h ; 2: Mouse Y delta