Extract "acia.asm" from shell
Also, come up with a way to make parts play well together memory-wise.
This commit is contained in:
Virgil Dupras
parent
ac22a206ae
commit
6bb454232a
@ -2,7 +2,37 @@
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Bits and pieces of code that you can assemble to build an OS for your machine.
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These parts are made to be glued together in a single `main.asm` file you write
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yourself.
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As of now, the z80 assembler code is written to be assembled with [scas][scas],
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but this is going to change in the future as a new hosted assembler is written.
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## Defines
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Each part can have its own constants, but some constant are made to be defined
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externally. We already have some of those external definitions in platform
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includes, but we can have more defines than this.
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Each part has a "DEFINES" section listing the constant it expects to be defined.
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Make sure that you have these constants defined before you include the file.
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## Variable management
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Each part can define variables. These variables are defined as addresses in
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RAM. We know where RAM start from the `RAMSTART` constant in platform includes,
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but because those parts are made to be glued together in no pre-defined order,
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we need a system to align variables from different modules in RAM.
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This is why each part that has variable expect a `<PARTNAME>_RAMSTART`
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constant to be defined and, in turn, defines a `<PARTNAME>_RAMEND` constant to
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carry to the following part.
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Thus, code that glue parts together coould look like:
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MOD1_RAMSTART .equ RAMSTART
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#include "mod1.asm"
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MOD2_RAMSTART .equ MOD1_RAMEND
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#include "mod2.asm"
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[scas]: https://github.com/KnightOS/scas
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97
parts/acia.asm
Normal file
97
parts/acia.asm
Normal file
@ -0,0 +1,97 @@
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; acia
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;
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; Manage I/O from an asynchronous communication interface adapter (ACIA).
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; provides "aciaPutC" to put c char on the ACIA as well as an input buffer.
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; You have to call "aciaInt" on interrupt for this module to work well.
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;
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; "aciaInit" also has to be called on boot, but it doesn't call "ei" and "im 1",
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; which is the responsibility of the main asm file, but is needed.
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; *** DEFINES ***
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; ACIA_CTL: IO port for the ACIA's control registers
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; ACIA_IO: IO port for the ACIA's data registers
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; ACIA_RAMSTART: Address at which ACIA-related variables should be stored in
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; RAM.
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; *** CONSTS ***
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; size of the input buffer. If our input goes over this size, we echo
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; immediately.
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ACIA_BUFSIZE .equ 0x20
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; *** VARIABLES ***
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; Our input buffer starts there
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ACIA_BUF .equ ACIA_RAMSTART
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; index, in the buffer, where our next character will go. 0 when the buffer is
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; empty, BUFSIZE-1 when it's almost full.
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ACIA_BUFIDX .equ ACIA_BUF+ACIA_BUFSIZE
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ACIA_RAMEND .equ ACIA_BUFIDX+1
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aciaInit:
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; initialize variables
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xor a
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ld (ACIA_BUFIDX), a ; starts at 0
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; setup ACIA
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; CR7 (1) - Receive Interrupt enabled
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; CR6:5 (00) - RTS low, transmit interrupt disabled.
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; CR4:2 (101) - 8 bits + 1 stop bit
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; CR1:0 (10) - Counter divide: 64
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ld a, 0b10010110
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out (ACIA_CTL), a
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ret
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; read char in the ACIA and put it in the read buffer
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aciaInt:
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push af
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push hl
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; Read our character from ACIA into our BUFIDX
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in a, (ACIA_CTL)
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bit 0, a ; is our ACIA rcv buffer full?
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jr z, .end ; no? a interrupt was triggered for nothing.
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call aciaBufPtr ; HL set, A set
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; is our input buffer full? If yes, we don't read anything. Something
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; is wrong: we don't process data fast enough.
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cp ACIA_BUFSIZE
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jr z, .end ; if BUFIDX == BUFSIZE, our buffer is full.
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; increase our buf ptr while we still have it in A
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inc a
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ld (ACIA_BUFIDX), a
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in a, (ACIA_IO)
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ld (hl), a
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.end:
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pop hl
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pop af
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ei
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reti
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; Set current buffer pointer in HL. The buffer pointer is where our *next* char
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; will be written. A is set to the value of (BUFIDX)
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aciaBufPtr:
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push bc
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ld a, (ACIA_BUFIDX)
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ld hl, ACIA_BUF
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xor b
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ld c, a
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add hl, bc ; hl now points to INPTBUF + BUFIDX
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pop bc
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ret
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; spits character in A in port SER_OUT
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aciaPutC:
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push af
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.stwait:
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in a, (ACIA_CTL) ; get status byte from SER
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bit 1, a ; are we still transmitting?
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jr z, .stwait ; if yes, wait until we aren't
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pop af
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out (ACIA_IO), a ; push current char
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ret
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81
parts/shell.asm
Normal file
81
parts/shell.asm
Normal file
@ -0,0 +1,81 @@
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; shell
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;
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; Runs a shell over an asynchronous communication interface adapter (ACIA).
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; for now, this unit is tightly coupled to acia.asm, but it will eventually be
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; more general than that.
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; Incomplete. For now, this outputs a welcome prompt and then waits for input.
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; Whenever input is CR or LF, we echo back what we've received and empty the
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; input buffer. This also happen when the buffer is full.
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; *** CONSTS ***
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CR .equ 0x0d
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LF .equ 0x0a
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shellInit:
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; print prompt
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ld hl, d_welcome
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call printstr
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call printcrlf
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ret
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shellLoop:
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call chkbuf
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jr shellLoop
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; print null-terminated string pointed to by HL
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printstr:
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ld a, (hl) ; load character to send
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or a ; is it zero?
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ret z ; if yes, we're finished
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call aciaPutC
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inc hl
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jr printstr
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; no ret because our only way out is ret z above
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printcrlf:
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ld a, CR
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call aciaPutC
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ld a, LF
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call aciaPutC
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ret
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; check if the input buffer is full or ends in CR or LF. If it does, prints it
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; back and empty it.
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chkbuf:
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call aciaBufPtr
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cp 0
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ret z ; BUFIDX is zero? nothing to check.
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cp ACIA_BUFSIZE
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jr z, .do ; if BUFIDX == BUFSIZE? do!
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; our previous char is in BUFIDX - 1. Fetch this
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dec hl
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ld a, (hl) ; now, that's our char we have in A
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inc hl ; put HL back where it was
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cp CR
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jr z, .do ; char is CR? do!
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cp LF
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jr z, .do ; char is LF? do!
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; nothing matched? don't do anything
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ret
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.do:
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; terminate our string with 0
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xor a
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ld (hl), a
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; reset buffer index
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ld (ACIA_BUFIDX), a
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; alright, let's go!
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ld hl, ACIA_BUF
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call printstr
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call printcrlf
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ret
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; *** DATA ***
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d_welcome: .byte "Welcome to Collapse OS", 0
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@ -1,177 +0,0 @@
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; shell
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;
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; Runs a shell over an asynchronous communication interface adapter (ACIA).
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; Incomplete. For now, this outputs a welcome prompt and then waits for input.
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; Whenever input is CR or LF, we echo back what we've received and empty the
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; input buffer. This also happen when the buffer is full.
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#include "platform.inc"
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; *** CONSTS ***
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CR .equ 0x0d
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LF .equ 0x0a
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; size of the input buffer. If our input goes over this size, we echo
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; immediately.
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BUFSIZE .equ 0x20
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; *** VARIABLES ***
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; Our input buffer starts there
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INPTBUF .equ RAMSTART
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; index, in the buffer, where our next character will go. 0 when the buffer is
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; empty, BUFSIZE-1 when it's almost full.
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BUFIDX .equ INPTBUF+BUFSIZE
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; *** CODE ***
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jr init
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.fill 0x38-$
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jr handleInterrupt
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init:
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di
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; setup stack
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ld hl, RAMEND
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ld sp, hl
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; initialize variables
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xor a
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ld (BUFIDX), a ; starts at 0
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; RC2014's serial I/O is based on interrupt mode 1. We'd prefer im 2,
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; but for now, let's go with the simpler im 1.
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im 1
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; setup ACIA
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; CR7 (1) - Receive Interrupt enabled
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; CR6:5 (00) - RTS low, transmit interrupt disabled.
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; CR4:2 (101) - 8 bits + 1 stop bit
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; CR1:0 (10) - Counter divide: 64
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ld a, 0b10010110
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out (ACIA_CTL), a
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; print prompt
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ld hl, d_welcome
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call printstr
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call printcrlf
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; alright, ready to receive
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ei
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mainloop:
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call chkbuf
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jr mainloop
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; read char in the ACIA and put it in the read buffer
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handleInterrupt:
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push af
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push hl
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; Read our character from ACIA into our BUFIDX
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in a, (ACIA_CTL)
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bit 0, a ; is our ACIA rcv buffer full?
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jr z, .end ; no? a interrupt was triggered for nothing.
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call getbufptr ; HL set, A set
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; is our input buffer full? If yes, we don't read anything. Something
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; is wrong: we don't process data fast enough.
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cp BUFSIZE
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jr z, .end ; if BUFIDX == BUFSIZE, our buffer is full.
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; increase our buf ptr while we still have it in A
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inc a
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ld (BUFIDX), a
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in a, (ACIA_IO)
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ld (hl), a
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.end:
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pop hl
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pop af
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ei
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reti
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; spits character in A in port SER_OUT
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printc:
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push af
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.stwait:
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in a, (ACIA_CTL) ; get status byte from SER
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bit 1, a ; are we still transmitting?
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jr z, .stwait ; if yes, wait until we aren't
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pop af
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out (ACIA_IO), a ; push current char
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ret
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; print null-terminated string pointed to by HL
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printstr:
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ld a, (hl) ; load character to send
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or a ; is it zero?
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ret z ; if yes, we're finished
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call printc
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inc hl
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jr printstr
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; no ret because our only way out is ret z above
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printcrlf:
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ld a, CR
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call printc
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ld a, LF
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call printc
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ret
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; check if the input buffer is full or ends in CR or LF. If it does, prints it
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; back and empty it.
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chkbuf:
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call getbufptr
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cp 0
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ret z ; BUFIDX is zero? nothing to check.
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cp BUFSIZE
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jr z, .do ; if BUFIDX == BUFSIZE? do!
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; our previous char is in BUFIDX - 1. Fetch this
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dec hl
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ld a, (hl) ; now, that's our char we have in A
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inc hl ; put HL back where it was
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cp CR
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jr z, .do ; char is CR? do!
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cp LF
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jr z, .do ; char is LF? do!
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; nothing matched? don't do anything
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ret
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.do:
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; terminate our string with 0
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xor a
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ld (hl), a
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; reset buffer index
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ld (BUFIDX), a
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; alright, let's go!
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ld hl, INPTBUF
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call printstr
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call printcrlf
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ret
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; Set current buffer pointer in HL. The buffer pointer is where our *next* char
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; will be written. A is set to the value of (BUFIDX)
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getbufptr:
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push bc
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ld a, (BUFIDX)
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ld hl, INPTBUF
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xor b
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ld c, a
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add hl, bc ; hl now points to INPTBUF + BUFIDX
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pop bc
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ret
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; *** DATA ***
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d_welcome: .byte "Welcome to Collapse OS", 0
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@ -31,18 +31,69 @@ device I use in this recipe.
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### Gathering parts
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* `parts/platforms/rc2014.inc` as `platform.inc`
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* `parts/shell/shell.asm` as `shell.asm`
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* Collapse OS parts in `/path/to/parts`
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* [scas][scas]
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* [romwrite][romwrite] and its specified dependencies
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* [GNU screen][screen]
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* A FTDI-to-TTL cable to connect to the Serial I/O module of the RC2014
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### Write main.asm
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This is what your glue code would look like:
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```
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#include "platforms/rc2014.inc"
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jr init
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.fill 0x38-$
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jr aciaInt
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init:
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di
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; setup stack
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ld hl, RAMEND
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ld sp, hl
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im 1
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call aciaInit
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call shellInit
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ei
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call shellLoop
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ACIA_RAMSTART .equ RAMSTART
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#include "acia.asm"
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#include "shell.asm"
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```
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The `platform.inc` include is there to load all platform-specific constants
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(such as `RAMSTART` and `RAMEND`).
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Then come the reset vectors. If course, we have our first jump to our main init
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routine, and then we have a jump to the interrupt handler defined in `acia.asm`.
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We need to plug this one in so that we can receive characters from the ACIA.
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Then comes the usual `di` to aoid interrupts during init, and stack setup.
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We set interrupt mode to 1 because that's what `acia.asm` is written around.
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Then, we init ACIA, shell, enable interrupt and give control of the main loop
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to `shell.asm`.
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What comes below is actual code include from the acia and shell modules. As you
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can see, we need to tell each module where to put their variables. `shell.asm`
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doesn't have variables, but if it did, we would have a `SHELL_RAMSTART .equ
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ACIA_RAMEND` just below the `acia.asm` include. `ACIA_RAMEND` is defined in
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`acia.asm`.
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### Build the image
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We only have the shell to build, so it's rather straightforward:
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scas -o rom.bin shell.asm
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scas -I /path/to/parts -o rom.bin main.asm
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### Write to the ROM
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Reference in New Issue
Block a user