sms/kbd: PS/2 driver WIP

blk/620

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 Sega Master System Recipe
 
 622 VDP                        630 PAD
+640 KBD

blk/640

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+( kbd - implement (ps2kc) for SMS PS/2 adapter )
+: (ps2kcA) ( for port A )
+( Before reading a character, we must first verify that there
+is something to read. When the adapter is finished filling its
+'164 up, it resets the latch, which output's is connected to
+TL. When the '164 is full, TL is low. Port A TL is bit 4 )
+    0xdc PC@ 0x10 AND IF 0 EXIT ( nothing ) THEN
+    0x3f PC@ DROP 0b11011101 ( Port A TH output, low ) 0x3f PC!
+    0xdc PC@ ( bit 3:0 go in 3:0 ) 0x0f AND ( n )
+    0b11111101 ( Port A TH output, high ) 0x3f PC!
+    0xdc PC@ ( bit 3:0 go in 7:4 ) 0x0f AND 4 LSHIFT OR ( n )
+	( Port A/B reset ) 0xff 0x3f PC!
+;
+

blk/641

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+: (ps2kcB) ( for port B )
+	( Port B TL is bit 2 )
+    0xdd PC@ 0x04 AND IF 0 EXIT ( nothing ) THEN
+    0x3f PC@ DROP 0b01110111 ( Port B TH output, low ) 0x3f PC!
+    0xdc PC@ ( bit 7:6 go in 1:0 ) 6 RSHIFT ( n )
+    0xdd PC@ ( bit 1:0 go in 3:2 ) 0x03 AND 2 LSHIFT OR ( n )
+    0b11110111 ( Port B TH output, high ) 0x3f PC!
+    0xdc PC@ ( bit 7:6 go in 5:4 ) 0xc0 AND 2 RSHIFT OR ( n )
+    0xdd PC@ ( bit 1:0 go in 7:6 ) 0x03 AND 6 LSHIFT OR ( n )
+	( Port A/B reset ) 0xff 0x3f PC!
+;