bdm-serial-core-v3.mu4

| This file is part of muforth: https://muforth.dev/
|
| Copyright 2002-2024 David Frech. (Read the LICENSE for details.)

loading S08 BDM support v3 (core)

__meta

hex

( Support for Freescale's S08 Background Debug Mode - or BDM.)

| I've split out the bit routines into two other files - one for the 908,
| and one for the S08. Look at bdm-bit-908.mu4 and bdm-bit-S08.mu4.

| It turns out that because the 9S08QG8, when mostly blank, is hard to get
| into Active BDM mode. On POR - power on reset - it starts running random
| code and either gets a COP - watchdog - reset, or an illegal instruction,
| or illegal address. So it resets and starts all over again. Trying to get
| into Active BDM via the BKGD pin is basically impossible. There is a
| forum posting about this here:
|
| http://forums.freescale.com/freescale/board/message?message.uid=11435#U11435
|
| So, given that, we have to hold BKGD/MS low during POR in order to force
| the chip into Active BDM mode. A side-effect of this is that it selects
| the bus clock - rather than the "alternate" BDM clock - ICSLCLK - so the
| BDM will be running at 4MHz instead of 8. This makes life simpler in some
| ways, but it turns out that it's pretty easy to meet the timing specs for
| both 4M and 8M BDM with a "host" running at less than 6M.

( Our signature.)
label id
   char S c,  char 0 c,  char 8 c,  ( S08 architecture)
   char b c,                        ( BDM)
   char 3 c,                        ( version 3)

| The SCI code is identical between 908 and S08 except for the names - and
| offsets - of the SCI status and data regs ... so let's abstract them.

.ifdef S08

macro SciStatus   SCIS1  ;m
macro SciData     SCID   ;m

.else   | 908

macro SciStatus   SCS1   ;m
macro SciData     SCDR   ;m

.then

macro SciRx?   begin  SciStatus 5 ( recvr full)  bset? until  ;m
macro SciTx?   begin  SciStatus 7 ( xmit empty)  bset? until  ;m

label SciRx  ( store byte into buf at HX, increment HX)
   SciRx?  SciData ) 0 ,x mov  rts  ;c

label SciTx  ( transmit byte from buf at HX, increment HX)
   SciTx?  0 ,x SciData ) mov  rts  ;c


( NOTE: Command numbers are all given in HEX.)

| dispatch uses the following stack frame:
| 0,s to 1,s   return addr to main loop
| 2,s to 5,s   send and expect buffer
| 6,s          send count
| 7,s          expect count
| 8,s          current count

label dispatch
   04 # cmp  u< if  ( 20..23 Send1..4)
      .a inc  6 ,s sta  ( send count)
      tsx  2 # aix  ( point HX at start of buffer)
      begin  SciRx c  .a decz? until
      rts
   then

   04 # sub
   03 # cmp  u< if  ( 24..26 Execute BDM, Expect 0..2)
      7 ,s sta  ( expect count)
      6 ,s lda  ( get send count)
      8 ,s sta  ( cur count)
      tsx  2 # aix  ( point HX at start of buffer)
      begin  BdmTx ) jsr  8 ,s decz? until  ( write bytes via BDM)

      | After writing bytes via BDM, delay. For an S08 target we should delay
      | 16 target cycles; for a CFv1 target, 32 cycles. Let's calculate,
      | based on our clock and assuming we are talking to a 4M target, how
      | many loops we need.

decimal

.ifdef cfv1-target   32 4 /
.else  ( S08)        16 4 /   .then

.ifdef 4.9152m       49 40    .else
.ifdef 9.8304m       98 40    .else
.ifdef 24m           24  4    .else
( assume 9.216M)     92 40    .then .then .then

hex
      */ ( count) # lda  begin .a decz? until  ( 4~ per loop)

      7 ,s lda  0= if  ( expect count is zero)
         SciTx j  ( send back a junk byte; keep host from outrunning us)
      then
      8 ,s sta  ( cur count)
      tsx  2 # aix  ( point HX at start of buffer)
      begin  BdmRx ) jsr  8 ,s decz? until  ( read bytes via BDM)

      7 ,s lda  ( get expect count)
      tsx  2 # aix  ( point HX at start of buffer)
      begin  SciTx c  .a decz? until  ( send response back via SCI)
      rts
   then

   03 # sub
   0= if  ( 27 SyncPulse)
      tsx  2 # aix  ( point HX at start of buffer)
      SyncPulse ) jsr
      SciTx c  SciTx j
   then

   .a decz? if  ( 28 BkgdLow)
      BdmDriveLow ) jmp  | drive BKGD/MS low
   then

   .a decz? if  ( 29 BkgdHiZ)
      BdmHiZ ) jmp
   then

   .a decz? if  ( 2a Set4M)
      BdmRx1 # ldhx
      SetRx1_4M ) jsr
      SetTx1_4M ) jmp
   then

   .a decz? if  ( 2b Set8M)
      BdmRx1 # ldhx
      SetRx1_8M ) jsr
      SetTx1_8M ) jmp
   then

.ifdef bdm-16m-target
   .a decz? if  ( 2c Set16M)
      BdmRx1 # ldhx
      SetRx1_16M ) jsr
      SetTx1_16M ) jmp
   then
.then

   ( Unknown)  ( do nothing at all!)  rts  ;c


\m bdm-chat-loop resolve>>  ( jump at start of Flash points here)

( Return a signature of who we are and what we're doing.)
label signon
   id # ldhx  5 # lda
   begin  SciTx c  .a decz? until

   -7 # ais   ( room for send and expect counts, cur count, and buffer)
   BdmHiZ ) jsr  ( make sure BKGD high and tri-stated)
   begin
      SciRx?  SciData ) lda  ( get command byte)
      20 # sub   ( BDM commands start at 20 hex; anything below that, we exit)
      u< if  ( 00 Bye up to 1f)  ( return to chat)  7 # ais  rts  then
      dispatch c
   again  ;c