gistfile1.txt

commit 388aeb278852e2a861a70c2e4ba5f39f01064571
Author: Vasily Khoruzhick <anarsoul@gmail.com>
Date:   Thu Dec 28 23:16:36 2023 -0800

    Add support for ay-4bit interface
    
    It's a custom interface and it requires custom ESP8266 firmware
    
    Description for Spectrum-side
    
    bits 0-3: D0-D3, bidirectional
    bit 4: CLK, active low, driven by Spectrum
    bit 5: DATA_READY (IRQ), active low, driven by ESP
    
    Read byte:
                    CLK D3 D2 D1 D0
                     1   x  x  x  x
                     0   0  1  0  1 <- start word for read, Spectrum drives
                                            D0-D3
                     1   x  x  x  x <- ESP will start driving D0-D3 here,
                                            but data can be considered
                                            valid only when CLK is 0
                     0  D3 D2 D1 D0 <- first nibble, ESP drives D0-D3
                     1   x  x  x  x <- ESP will start driving D0-D3 here,
                                            but data can be considered
                                            valid only when CLK is 0
                     0  D7 D6 D5 D4 <- second nibble, ESP drives D0-D3
                     1   x  x  x  x
                     0  C3 C2 C1 C0 <- Spectrum outputs checksum
                     1   x  x  x  x
    
    Write byte:
                    CLK D3 D2 D1 D0
                     1   x  x  x  x
                     0   1  0  1  0 <- start word for write, Spectrum drives
                                            D0-D3
                     1   x  x  x  x
                     0  D3 D2 D1 D0 <- first nibble, Spectrum drives D0-D3
                     1   x  x  x  x
                     0  D7 D6 D5 D4 <- second nibble, Spectrum drives D0-D3
                     1   x  x  x  x <- ESP will start driving D0-D3 here,
                                            but data can be considered
                                            valid only when CLK is 0
                     0  C3 C2 C1 C0 <- ESP outputs checksum
                     1   x  x  x  x
    
    Checksum is D3 ^ D7 << 3 | D2 ^ D6 << 2 | D1 ^ D5 << 1 | D0 ^ D4, i.e.
    xor of nibbles

diff --git a/Makefile b/Makefile
index 066aab2..d4258ce 100644
--- a/Makefile
+++ b/Makefile
@@ -31,7 +31,10 @@ zxuno-zxscreen: $(SOURCES)
 	sjasmplus main.asm -DUNO -DZXSCR --lst=main.lst -DV=$(VERSION)
 
 esxdos-ay: $(SOURCES)
-	sjasmplus main.asm -DAY -DZXSCR --lst=main.lst -DV=$(VERSION)
+	sjasmplus main.asm -DAY -DAYCOMMON -DZXSCR --lst=main.lst -DV=$(VERSION)
+
+esxdos-ay4bit: $(SOURCES)
+	sjasmplus main.asm -DAY4BIT -DAYCOMMON -DZXSCR --lst=main.lst -DV=$(VERSION)
 
 emu-timex: $(SOURCES)
 	sjasmplus main.asm -DEMU -DUNO -DTIMEX --lst=main.lst -DV=$(VERSION)
@@ -43,4 +46,4 @@ emu-zx: $(SOURCES)
 	sjasmplus main.asm -DEMU -DUNO -DZXSCR --lst=main.lst -DV=$(VERSION)
 
 clean:
-	rm $(BINARY) $(LST)
\ No newline at end of file
+	rm $(BINARY) $(LST)
diff --git a/drivers/ay-4bit.asm b/drivers/ay-4bit.asm
new file mode 100644
index 0000000..86b70d9
--- /dev/null
+++ b/drivers/ay-4bit.asm
@@ -0,0 +1,172 @@
+    module Uart
+
+init:
+    ld a, 0x07
+    ld bc, 0xfffd
+    out (c), a
+    ld a, 0xfc
+    ld b, 0xbf
+    out (c), a ; Enable read mode
+
+    ld a, 0x0e
+    ld bc, 0xfffd
+    out (c), a
+
+    ld b, 0xbf
+    ld a, 0b11111111
+    out (c), a
+
+.flush
+    in a, (c)
+    and a, 0b00100000
+    call z, read
+    jr .flush
+
+    ; byte is in a
+write:
+    push af
+    push bc
+    push de
+    di
+    ld bc, 0xfffd
+    ld a, 0x0e
+    out (c), a
+    ld b, 0xbf
+
+    ld e, a
+    ; 0b1010 is start word for write
+    ld a, 0b11111010
+    out (c), a
+    ; latch on falling edge
+    and a, 0b11101111
+    out (c), a
+
+    ld a, e
+    and a, 0b00001111
+    ; checksum
+    ld d, a
+    or a, 0b11110000
+    out (c), a
+    ; latch on falling edge
+    and a, 0b11101111
+    out (c), a
+    ld a, e
+
+    rrca
+    rrca
+    rrca
+    rrca
+
+    and a, 0b00001111
+    ; checksum
+    ld e, a
+    xor d
+    ld d, a
+    ld a, e
+
+    or a, 0b11110000
+    out (c), a
+    ; latch on falling edge
+    and a, 0b11101111
+    out (c), a
+
+    ld a, 0b11111111
+    out (c), a
+    ld a, 0b11101111
+    out (c), a
+
+    in a, (c)
+    and a, 0b00001111
+    cp a, d
+    jr nz, .error
+
+    ld a, 0b11111111
+    out (c), a
+    ei
+    pop de
+    pop bc
+    pop af
+    ret
+
+.error
+    ld a, 0b11111111
+    out (c), a
+    ei
+    pop de
+    pop bc
+    pop af
+    ret
+
+    ; returns byte in a
+read:
+    push bc
+    push de
+    di
+    ld bc, 0xfffd
+    ld a, 0x0e
+    out (c), a
+    ld b, 0xbf
+
+    ; ESP drives IRQ low if it's ready to transmit
+.wait
+    ld a, 0b11111111
+    out (c), a
+    in a, (c)
+    and a, 0b00100000
+    jr nz, .wait
+
+    ; 0b0101 is start word for read
+    ld a, 0b11110101
+    out (c), a
+    ; latch on falling edge
+    and a, 0b11101111
+    out (c), a
+
+    ; receive first nibble
+    ld a, 0b11111111
+    out (c), a
+    ; latch on falling edge
+    ld a, 0b11101111
+    out (c), a
+    in a, (c)
+    and a, 0b00001111
+    ; checksum is in d
+    ld d, a
+
+    ; receive second nibble
+    ld a, 0b11111111
+    out (c), a
+    ; latch on falling edge
+    ld a, 0b11101111
+    out (c), a
+    in a, (c)
+    and a, 0b00001111
+
+    ld e, a
+    rlca
+    rlca
+    rlca
+    rlca
+    ; d now contains received byte
+    or d
+    ld d, a
+    ld a, e
+    ; a now contains checksum in lower 4 bits
+    xor d
+    or a, 0b11110000
+    out (c), a
+    ; latch on falling edge
+    and a, 0b11101111
+    out (c), a
+
+    ld a, 0b11111111
+    out (c), a
+
+    ld a, d
+    pop de
+    pop bc
+
+    ei
+    ret
+
+    endmodule
diff --git a/drivers/index.asm b/drivers/index.asm
index 7bb59be..fc536ff 100644
--- a/drivers/index.asm
+++ b/drivers/index.asm
@@ -9,10 +9,14 @@
     IFDEF AY
     include "ay-uart.asm"
     ENDIF
-    
+
+    IFDEF AY4BIT
+    include "ay-4bit.asm"
+    ENDIF
+
     include "utils.asm"
     include "wifi.asm"
     include "proxy.asm"
     include "memory.asm"
     include "general-sound.asm"
-    
\ No newline at end of file
+    
diff --git a/gopher/render/ui.asm b/gopher/render/ui.asm
index 266ea92..ff95ac0 100644
--- a/gopher/render/ui.asm
+++ b/gopher/render/ui.asm
@@ -73,4 +73,10 @@ header db "    Moon Rabbit "
 header db "    Moon Rabbit "
        db VERSION_STRING
        db " for AYWIFI (c) 2021 Alexander Nihirash",13, 0
-    ENDIF
\ No newline at end of file
+    ENDIF
+
+    IFDEF AY4BIT
+header db "    Moon Rabbit "
+       db VERSION_STRING
+       db " for AY4BIT (c) 2021 Alexander Nihirash",13, 0
+    ENDIF
diff --git a/player/vortex-processor.asm b/player/vortex-processor.asm
index 22196e8..ed622e2 100644
--- a/player/vortex-processor.asm
+++ b/player/vortex-processor.asm
@@ -19,7 +19,7 @@ play:
 .stop
     call VTPL.MUTE
     
-    IFDEF AY
+    IFDEF AYCOMMON
     call restoreAyState
     ENDIF
 
@@ -29,7 +29,7 @@ play:
     xor a : ld (Render.play_next), a
     jr .stop
 
-    IFDEF AY
+    IFDEF AYCOMMON
 restoreAyState:
     ld a, #07
     ld bc, #fffd
@@ -47,4 +47,4 @@ restoreAyState:
 message db "Press key to stop...", 0
     ENDMODULE
     include "player.asm"
-    
\ No newline at end of file
+