From d50d162bc47945def5d6d6247074876c6fa97a1d Mon Sep 17 00:00:00 2001
From: Alan Cox <alan@linux.intel.com>
Date: Wed, 9 Jan 2019 22:19:49 +0000
Subject: [PATCH] z80sio: tidy up the macros a bit

We still need to think about how IM1 is best done
---
 Kernel/dev/z80sio.s | 250 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 250 insertions(+)
 create mode 100644 Kernel/dev/z80sio.s

diff --git a/Kernel/dev/z80sio.s b/Kernel/dev/z80sio.s
new file mode 100644
index 00000000..a5829cbc
--- /dev/null
+++ b/Kernel/dev/z80sio.s
@@ -0,0 +1,250 @@
+;
+;	SIO2 IM2 console driver
+;
+;	The buffers are 256 bytes per channel and page aligned. The lower
+;	half is used for receive the upper for transmit. Both are rings.
+
+;
+;	Transmit data from the queue. We need a stop system for this but
+;	actually the logical one might be to just turn that IRQ off, so long
+;	as we remember to kickstart it again properly. Check if it's enough
+;	to just unmask the IRQ bit ?
+;
+;	All of this lives in common space so we don't bank switch so much.
+
+.macro sio_ports X
+
+	.area	_SERIAL
+sio'X'_rx:
+	.ds	128
+sio'X'_tx:
+	.ds	128
+
+	.area _COMMONMEM
+sio'X'_error:
+	.db	0
+sio'X'_rxover:
+	.db	0
+sio'X'_stat:
+	.db	0
+sio'X'_txp:
+	.dw	sio'X'_tx
+sio'X'_txe:
+	.dw	sio'X'_tx
+sio'X'_rxp:
+	.dw	sio'X'_rx
+sio'X'_rxe:
+	.dw	sio'X'_rx
+
+.endm
+
+.macro sio_handler_im2 X CP DP RET
+
+;
+;	C interface methods
+;
+	.globl _sio'X'_txqueue
+	.globl _sio'X'_flow_control_off
+	.globl _sio'X'_flow_control_on
+	.globl _sio'X'_rx_get
+	.globl _sio'X'_error_get
+
+;
+;	Interrupt vector handler for port A transmit empty
+;
+sio'X'_txd:
+	push af
+	ld a,(_sio'X'_txl)
+	or a
+	jr z, tx_'X'_none
+	push hl
+	dec a
+	ld (_sio'X'_txl),a
+	ld hl,(sio'X'_txp)
+	ld a,(hl)
+	out (DP),a
+	inc hl
+	set 7,l
+	ld (sio'X'_txp),hl
+	pop hl
+tx_'X'_none:
+	ld a,#0x28
+	out (CP),a		; silence tx interrupt
+	pop af
+	ei
+	RET
+;
+;	Interrupt vector handler for port A receive ready
+;
+sio'X'_rx_ring:
+	push af
+	push hl
+sio'X'_rx_next:
+	in a,(DP)		; read ASAP
+	ld l,a
+	ld a,(_sio'X'_rxl)
+	inc a
+	jp m, 'X'_rx_over
+	ld (_sio'X'_rxl),a
+	; should we check bit 5/6 and if appropriate flow control on bit 5/6
+	; high ?
+	cp #0x60		; flow control threshold
+	call z, _sio'X'_flow_control_on
+	ld a,l
+	ld hl,(sio'X'_rxp)
+	ld (hl),a
+	inc l
+	res 7,l
+	ld (sio'X'_rxp),hl
+	;
+	;	The chip has a small FIFO and bytes can also arrive as we
+	;	read. To maximise performance try and empty it each time.
+	;
+	;	This is bounded as worst case at high data rate and low
+	;	CPU speed we will overrun and bail out.
+	;
+	in a,(CP)		; RR 0
+	rra
+	jr c, sio'X'_rx_next
+	pop hl
+	pop af
+	ei
+	RET
+'X'_rx_over:
+	ld a,(sio'X'_error)
+	or #0x20		; Fake an RX overflow bit
+	ld (sio'X'_rxover),a
+	pop af
+	ei
+	RET
+;
+;	Interrupt vector for a port A status change
+;
+sio'X'_status:
+	; CTS or DCD change
+	push af
+	push hl
+	; RR0
+	in a,(CP)
+	ld (_sio'X'_state),a
+	and #8
+	jr z, no_dcd_drop_'X
+	; \DCD went high
+	ld (_sio'X'_dropdcd),a		; Set the dcdflag
+no_dcd_drop_'X':
+	; Clear the latched values
+	ld a,#0x10
+	out (CP),a
+	pop hl
+	pop af
+	ei
+	RET
+
+;
+;	Interrupt vector for a port A error
+;
+sio'X'_special:
+	; Parity, RX Overrun, Framing
+	; Probably want to record them, but we at least must clean up
+	push af
+	ld a,#1
+	out (CP),a		; RR1 please
+	in a,(CP)		; clear events
+	ld (sio'X'_error),a	; Save error bits
+	; Clear the latched values
+	ld a,#0x30
+	out (CP),a
+	pop af
+	ei
+	RET
+
+;
+;	Queue a byte to be sent (DI required)
+;
+;	l = byte
+;
+;	Need a way to halt processing somewhere here or a_tx ?
+;	(or can we use hardware ?)
+;	128 byte ring buffer aligned to upper half (rx is in lower)
+;
+_sio'X'_txqueue:
+	ld a,(_sio'X'_txl)
+	or a
+	jr z, sio'X'_direct_maybe	; if can tx now then do
+	inc a
+	jp m, tx'X'_overflow
+sio'X'_queue:
+	ld (_sio'X'_txl),a
+	ld a,l
+	ld hl,(sio'X'_txe)
+	ld (hl),a
+	inc l
+	set 7,l
+	ld (sio'X'_txe),hl
+	ld l,#0
+	ret
+tx'X'_overflow:
+	; some kind of flag for error
+	ld l,#1
+	ret
+sio'X'_direct_maybe:
+	; check RR
+	in a,(CP)
+	and #0x04		; RX space ?
+	; if space
+	ld a,#1
+	jr z, sio'X'_queue
+	; bypass the queue and kickstart the interrupt machine
+	ld a,l
+	out (DP),a
+	ld l,#0
+	ret
+	; Call with DI
+
+_sio'X'_flow_control_off:
+	ld a,#5
+	out(CP),a		; WR 5
+	ld a,(_sio'X'_wr5)
+	out (CP),a		; Turn off RTS
+	ret
+
+_sio'X'_flow_control_on:
+	ld a,#5
+	out(CP),a		; WR 5
+	ld a,(_sio'X'_wr5)
+	and #0xFD
+	out (CP),a		; Turn off RTS
+	ret
+
+	; DI required
+	; Returns char in L
+	;
+	; Caller responsible for making post buffer fetch decisions about
+	; RTS
+_sio'X'_rx_get:
+	ld a,(_sio'X'_rxl)
+	or a
+	ret z
+	dec a
+	ld (_sio'X'_rxl),a
+	ld hl,(sio'X'_rxe)
+	ld a,(hl)
+	inc l
+	res 7,l
+	ld (sio'X'_rxe),hl
+	scf
+	ld l,a
+	ret
+
+	; DI required
+_sio'X'_error_get:
+	ld hl,#sio'X'_error
+	ld a,(hl)
+	ld (hl),#0
+	ld l,a
+	ret
+
+
+.endm
+
+	
\ No newline at end of file
-- 
2.34.1