m68k/atari: fix SCC initialization for debug console

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@telegraphics.com.au>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

1 files changed, 21 insertions, 10 deletions

diff --git a/arch/m68k/kernel/head.S b/arch/m68k/kernel/head.S
index b671f07aeb81..15c8f55e4835 100644
--- a/arch/m68k/kernel/head.S
+++ b/arch/m68k/kernel/head.S
@@ -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 */
@@ -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)