Hi Finn,
according to the old driver source, all Ataris except for the TT use a
3.672 MHz clock at RTxC[A,B] for both the 9600 and 38400 baud
settings. Most lower baud rates use the 8 MHz PCLK input.
Divisors are 24 (9600 baud) and 6 (38400 baud) in that case.
The TT uses that same arrangement on channel A, but something very
different on channel B - 307.2 kHz at RTxCB and 2.4576 MHz on TRxCB.
Divisors are 2 (using RTxCB) and 4 (using TRxCB), resepectively.
Adding all that in would complicate the code too much - let's settle
for a comment in the code to say SCC_B should not be used on the TT
without fixing the init table.
See page 1181 of the Profibuch - that corresponds well with the old
SCC driver source (can send that by PM should you need it).
Further comment inline.
Cheers,
Michael
On Tue, May 27, 2014 at 1:29 AM, Finn Thain <fthain@xxxxxxxxxxxxxxxxxxx> wrote:
Fix SCC initialization for Atari as was previously fixed for Mac. It's
probably not practical to share more code but some attempt is made to
align the Mac and Atari variants.
Signed-off-by: Finn Thain <fthain@xxxxxxxxxxxxxxxxxxx>
---
This patch needs testing on Atari. It can't be tested without editing
macro definitions to enable SCC debug output (which also means disabling
MFP debug output).
Changed in v2: drop the baud rate change
---
arch/m68k/kernel/head.S | 31 +++++++++++++++++++++----------
1 file changed, 21 insertions(+), 10 deletions(-)
Index: linux-m68k/arch/m68k/kernel/head.S
===================================================================
--- linux-m68k.orig/arch/m68k/kernel/head.S 2014-05-26 23:13:50.000000000 +1000
+++ linux-m68k/arch/m68k/kernel/head.S 2014-05-26 23:24:33.000000000 +1000
@@ -2722,6 +2722,7 @@ func_return get_new_page
#define MAC_USE_SCC_B /* Printer port */
#if defined(MAC_USE_SCC_A) || defined(MAC_USE_SCC_B)
+/* Initialisation table for SCC with 3.6864 MHz PCLK */
L(scc_initable_mac):
.byte 4,0x44 /* x16, 1 stopbit, no parity */
.byte 3,0xc0 /* receiver: 8 bpc */
@@ -2744,14 +2745,12 @@ L(scc_initable_mac):
#define USE_MFP
#if defined(USE_SCC_A) || defined(USE_SCC_B)
-#define USE_SCC
-/* Initialisation table for SCC */
-L(scc_initable):
- .byte 9,12 /* Reset */
+/* Initialisation table for SCC with 7.9872 MHz PCLK */
+/* PCLK == 8.0539 gives baud == 9680.1 */
+L(scc_initable_atari):
.byte 4,0x44 /* x16, 1 stopbit, no parity */
.byte 3,0xc0 /* receiver: 8 bpc */
.byte 5,0xe2 /* transmitter: 8 bpc, assert dtr/rts */
- .byte 9,0 /* no interrupts */
.byte 10,0 /* NRZ */
.byte 11,0x50 /* use baud rate generator */
.byte 12,24,13,0 /* 9600 baud */
Would be 6 instead of 24 here for 38400, presumably?
@@ -2800,7 +2799,7 @@ LMFP_UDR = 0xfffa2f
*/
/*
- * Initialize serial port hardware for 9600/8/1
+ * Initialize serial port hardware
*/
func_start serial_init,%d0/%d1/%a0/%a1
/*
@@ -2810,7 +2809,7 @@ func_start serial_init,%d0/%d1/%a0/%a1
* d0 = boot info offset
* CONFIG_ATARI
* a0 = address of SCC
- * a1 = Liobase address/address of scc_initable
+ * a1 = Liobase address/address of scc_initable_atari
* d0 = init data for serial port
* CONFIG_MAC
* a0 = address of SCC
@@ -2846,9 +2845,21 @@ func_start serial_init,%d0/%d1/%a0/%a1
moveb %a1@(LPSG_READ),%d0
bset #5,%d0
moveb %d0,%a1@(LPSG_WRITE)
-#elif defined(USE_SCC)
+#elif defined(USE_SCC_A) || defined(USE_SCC_B)
lea %a1@(LSCC_CTRL),%a0
- lea %pc@(L(scc_initable)),%a1
+ /* Reset SCC register pointer */
+ moveb %a0@,%d0
+ /* Reset SCC device: write register pointer then register value */
+ moveb #9,%a0@
+ moveb #0xc0,%a0@
+ /* Wait for 5 PCLK cycles, which is about 63 CPU cycles */
+ /* 5 / 7.9872 MHz = approx. 0.63 us = 63 / 100 MHz */
+ movel #32,%d0
+2:
+ subq #1,%d0
+ jne 2b
+ /* Initialize channel */
+ lea %pc@(L(scc_initable_atari)),%a1
2: moveb %a1@+,%d0
jmi 3f
moveb %d0,%a0@
@@ -3017,7 +3028,7 @@ func_start serial_putc,%d0/%d1/%a0/%a1
nop
bset #5,%d0
moveb %d0,%a1@(LPSG_WRITE)
-#elif defined(USE_SCC)
+#elif defined(USE_SCC_A) || defined(USE_SCC_B)
3: btst #2,%a1@(LSCC_CTRL)
jeq 3b
moveb %d0,%a1@(LSCC_DATA)
--
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