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-rw-r--r--protocol/adb.c54
1 files changed, 39 insertions, 15 deletions
diff --git a/protocol/adb.c b/protocol/adb.c
index 9e8d76832d..a92e81f1f6 100644
--- a/protocol/adb.c
+++ b/protocol/adb.c
@@ -199,24 +199,48 @@ static inline bool read_bit(void)
{
// ADB Bit Cells
//
- // bit0: ______~~~
- // 65 :35us
+ // bit cell time: 70-130us
+ // low part of bit0: 60-70% of bit cell
+ // low part of bit1: 30-40% of bit cell
//
- // bit1: ___~~~~~~
- // 35 :65us
+ // bit cell time 70us 130us
+ // --------------------------------------------
+ // low part of bit0 42-49 78-91
+ // high part of bit0 21-28 39-52
+ // low part of bit1 21-28 39-52
+ // high part of bit1 42-49 78-91
//
- // bit0 low time: 60-70% of bit cell(42-91us)
- // bit1 low time: 30-40% of bit cell(21-52us)
- // bit cell time: 70-130us
- // [from Apple IIgs Hardware Reference Second Edition]
//
- // After 55us if data line is low/high then bit is 0/1.
- // Too simple to rely on?
+ // bit0:
+ // 70us bit cell:
+ // ____________~~~~~~
+ // 42-49 21-28
+ //
+ // 130us bit cell:
+ // ____________~~~~~~
+ // 78-91 39-52
+ //
+ // bit1:
+ // 70us bit cell:
+ // ______~~~~~~~~~~~~
+ // 21-28 42-49
+ //
+ // 130us bit cell:
+ // ______~~~~~~~~~~~~
+ // 39-52 78-91
+ //
+ // read:
+ // ________|~~~~~~~~~
+ // 55us
+ // Read data line after 55us. If data line is low/high then bit is 0/1.
+ // This method might not work at <90us bit cell time.
+ //
+ // [from Apple IIgs Hardware Reference Second Edition]
bool bit;
- wait_data_lo(75); // wait the beginning of bit cell
+ wait_data_lo(75); // wait the start of bit cell at least 130ms(55+0+75)
_delay_us(55);
bit = data_in();
- wait_data_hi(36); // wait high part of bit cell
+ wait_data_hi(36); // wait high part of bit cell at least 91ms(55+36)
return bit;
}
@@ -258,7 +282,7 @@ Resources
---------
ADB - The Untold Story: Space Aliens Ate My Mouse
http://developer.apple.com/legacy/mac/library/#technotes/hw/hw_01.html
-Apple IIgs Hardware Reference Second Edition [p80(Chapter6 p121)]
+Apple IIgs Hardware Reference Second Edition [Chapter6 p121]
ftp://ftp.apple.asimov.net/pub/apple_II/documentation/Apple%20IIgs%20Hardware%20Reference.pdf
ADB Keycode
http://72.0.193.250/Documentation/macppc/adbkeycodes/
@@ -376,9 +400,9 @@ Communication
Global reset:
Host asserts low in 2.8-5.2ms. All devices are forced to reset.
- Send request from device(Srq):
+ Service request from device(Srq):
Device can request to send at commad(Global only?) stop bit.
- keep low for 300us to request.
+ Requesting device keeps low for 140-260us at stop bit of command.
Keyboard Data(Register0)