1 files changed, 27 insertions, 16 deletions
diff --git a/fpga/src/I2C.bs b/fpga/src/I2C.bs
index 292691b..2752acd 100644
--- a/fpga/src/I2C.bs
+++ b/fpga/src/I2C.bs
@@ -8,7 +8,8 @@ struct I2CStatus =
   { -- | This bit is low when a message is being sent, and gets raised after:
     --
     -- - We finished sending an address, but a NACK was received.
-    -- - We finished reading a byte, including sending an ACK or NACK bit.
+    -- - We finished reading a byte, including starting to send an ACK or NACK
+    --   bit.
     -- - We finished writing a byte, including reading an ACK or NACK bit.
     --
     -- When this bit is `True`, writing to it will cause a new read or write,
@@ -23,10 +24,10 @@ struct I2CStatus =
     busIdle :: Bool
   ; -- | The last ACK bit we received from sending an address. Writing to this
     -- bit does not affect the internal state of the I²C controller.
-    addrAck :: Bool
+    addrAckBit :: Bool
   ; -- | The last ACK bit we received during a write, or the next ACK bit we'll
     -- send during a read.
-    dataAck :: Bool
+    dataAckBit :: Bool
   ; -- | A flag set if we detect during a START condition that we've lost
     -- arbitration. If this occurs, no read or write will occur, and the read
     -- or write should be retried later. Writing to this bit does not affect
@@ -69,7 +70,7 @@ data I2CBusState
     SendAddrBitWait (Bit 3) (Bit 1)
   | -- | We're sending an address, and about to lower SCL.
     SendAddrBitLowerSCL (Bit 3) (Bit 1)
-  | -- | We're lowering SDA as part of getting the ACK bit after sending an
+  | -- | We're raising SDA as part of getting the ACK bit after sending an
     -- address.
     GetAddrAckSDA
   | -- | We're raising SCL to start the clock cycle in which we'll get the ACK
@@ -105,13 +106,15 @@ mkI2C' :: Bit 1 -> Bit 1 -> Wire (Bit 1) -> Wire (Bit 1) -> Reg (Bit 8) ->
   Reg (Bit 8) -> Reg I2CStatus -> Module ()
 mkI2C' rxSCL rxSDA txSCL txSDA addrReg dataReg statusReg = module
   state :: Reg I2CBusState <- mkReg Idle
+  savedAddr :: Reg (Bit 8) <- mkReg 0
+  savedData :: Reg (Bit 8) <- mkReg 0
   rules
     "debug": when True ==> $display (fshow state)
-    "remain Idle": when Idle <- state, statusReg.notBusy ==> do
+    "remain Idle": when Idle <- state, statusReg.ready ==> do
       state := Idle
       txSCL := 1
       txSDA := 1
-    "triggered from Idle": when Idle <- state, not statusReg.notBusy ==>
+    "triggered from Idle": when Idle <- state, not statusReg.ready ==>
       if rxSDA == 0 then do
         statusReg := statusReg { ready = True; busIdle = True; arbitrationLost = True }
         state := Idle
@@ -123,10 +126,14 @@ mkI2C' rxSCL rxSDA txSCL txSDA addrReg dataReg statusReg = module
         txSDA := 0
     "StartSDA": when StartSDA <- state ==> do
       state := SendAddrBitSDA 7
+      savedAddr := addrReg
+      savedData := if savedAddr[0:0] == 1 -- R/!W
+                   then 0 -- R
+                   else dataReg -- !W
       txSCL := 0
       txSDA := 0
     "SendAddrBitSDA": when SendAddrBitSDA n <- state ==> do
-      let bit = addrReg[n:n]
+      let bit = savedAddr[n:n]
       state := SendAddrBitRaiseSCL n bit
       txSCL := 0
       txSDA := bit
@@ -147,16 +154,16 @@ mkI2C' rxSCL rxSDA txSCL txSDA addrReg dataReg statusReg = module
     "GetAddrAckSDA": when GetAddrAckSDA <- state ==> do
       state := GetAddrAckRaiseSCL
       txSCL := 0
-      txSDA := 0
+      txSDA := 1
     "GetAddrAckRaiseSCL": when GetAddrAckRaiseSCL <- state ==> do
       state := GetAddrAckReadSDA
       txSCL := 1
       txSDA := 1
     "GetAddrAckReadSDA": when GetAddrAckReadSDA <- state ==> do
-      statusReg := statusReg { addrAck = unpack rxSDA }
+      statusReg := statusReg { addrAckBit = unpack rxSDA }
       state := if rxSDA == 1 -- NACK
                then TODO
-               else if addrReg[0:0] == 0 -- R/!W
+               else if savedAddr[0:0] == 0 -- R/!W
                then TODO -- !W
                else ReadLowerSCL 7 1
       txSCL := 1
@@ -172,7 +179,7 @@ mkI2C' rxSCL rxSDA txSCL txSDA addrReg dataReg statusReg = module
       txSCL := 1
       txSDA := 1
     "ReadReadSDA": when ReadReadSDA n <- state ==> do
-      dataReg := dataReg [6:0] ++ rxSDA
+      savedData := savedData [6:0] ++ rxSDA
       state := if n == 0
                then ReadAckLowerSCL
                else ReadLowerSCL (n - 1) 1
@@ -183,14 +190,18 @@ mkI2C' rxSCL rxSDA txSCL txSDA addrReg dataReg statusReg = module
       txSCL := 0
       txSDA := 1
     "ReadAckWriteSDA": when ReadAckWriteSDA <- state ==> do
-      let bit = pack statusReg.dataAck
+      let bit = pack statusReg.dataAckBit
+      statusReg := statusReg { ready = True }
+      dataReg := savedData
       state := ReadAckRaiseSCL bit 1
       txSCL := 0
       txSDA := bit
     "ReadAckRaiseSCL": when ReadAckRaiseSCL bit time <- state ==> do
       state := if time == 1
                then ReadAckRaiseSCL bit (time - 1)
-               else TODO
+               else if bit == 0
+               then ReadLowerSCL 7 1 -- ACK
+               else TODO -- NACK
       txSCL := 1
       txSDA := bit
   return ()
@@ -204,10 +215,10 @@ mkI2C rxSCL rxSDA = module
   addrReg <- mkReg 0
   dataReg <- mkReg 0
   statusReg <- mkReg (I2CStatus
-    { notBusy = False
+    { ready = True
     ; busIdle = False
-    ; addrAck = False
-    ; dataAck = False
+    ; addrAckBit = False
+    ; dataAckBit = False
     ; arbitrationLost = False
     ; rsvd = 0
     })