* [RFC 4/4] m68k/atari: fix SCC initialization for debug console
@ 2014-03-02 23:56 Finn Thain
2014-03-04 0:34 ` Michael Schmitz
0 siblings, 1 reply; 3+ messages in thread
From: Finn Thain @ 2014-03-02 23:56 UTC (permalink / raw)
To: linux-m68k
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.
---
One problem with this patch is that it fixes a problem that doesn't affect
anyone (as long as Atari SCC debugging remains disabled).
The line rate is changed to 38400 baud to match the Mac code (which
follows the pmac_zilog serial console default). It would be nice to
standardize but I don't know whether this is realistic.
The 7.9872 MHz PCLK used in this patch was inferred from the existing code
as I don't have any hardware data.
This patch is untested on Atari.
---
arch/m68k/kernel/head.S | 34 ++++++++++++++++++++++------------
1 file changed, 22 insertions(+), 12 deletions(-)
Index: linux-m68k/arch/m68k/kernel/head.S
===================================================================
--- linux-m68k.orig/arch/m68k/kernel/head.S 2014-03-03 10:30:01.000000000 +1100
+++ linux-m68k/arch/m68k/kernel/head.S 2014-03-03 10:30:32.000000000 +1100
@@ -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 */
@@ -2744,17 +2745,14 @@ 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 */
- .byte 4,0x44 /* x16, 1 stopbit, no parity */
+/* Initialisation table for SCC with 7.9872 MHz PCLK */
+L(scc_initable_atari):
+ .byte 4,0x04 /* x1, 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 */
+ .byte 12,102,13,0 /* 38400 baud */
.byte 14,2,14,3 /* use master clock for BRG, enable */
.byte 3,0xc1 /* enable receiver */
.byte 5,0xea /* enable transmitter */
@@ -2800,7 +2798,7 @@ 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 +2808,7 @@ 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 +2844,21 @@ 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 +3027,7 @@ 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)
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [RFC 4/4] m68k/atari: fix SCC initialization for debug console
2014-03-02 23:56 [RFC 4/4] m68k/atari: fix SCC initialization for debug console Finn Thain
@ 2014-03-04 0:34 ` Michael Schmitz
2014-03-04 2:31 ` Finn Thain
0 siblings, 1 reply; 3+ messages in thread
From: Michael Schmitz @ 2014-03-04 0:34 UTC (permalink / raw)
To: Finn Thain; +Cc: linux-m68k
Hi Finn,
On Mon, Mar 3, 2014 at 12:56 PM, Finn Thain <fthain@telegraphics.com.au> 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.
>
> ---
> One problem with this patch is that it fixes a problem that doesn't affect
> anyone (as long as Atari SCC debugging remains disabled).
>
> The line rate is changed to 38400 baud to match the Mac code (which
> follows the pmac_zilog serial console default). It would be nice to
> standardize but I don't know whether this is realistic.
>
> The 7.9872 MHz PCLK used in this patch was inferred from the existing code
> as I don't have any hardware data.
The difference in clock source settings is the main reason we can't
use the exact same code IIRC.
> This patch is untested on Atari.
I can do that - good excuse to reenable the SCC debugging anyway.
Cheers,
Michael
>
> ---
> arch/m68k/kernel/head.S | 34 ++++++++++++++++++++++------------
> 1 file changed, 22 insertions(+), 12 deletions(-)
>
> Index: linux-m68k/arch/m68k/kernel/head.S
> ===================================================================
> --- linux-m68k.orig/arch/m68k/kernel/head.S 2014-03-03 10:30:01.000000000 +1100
> +++ linux-m68k/arch/m68k/kernel/head.S 2014-03-03 10:30:32.000000000 +1100
> @@ -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 */
> @@ -2744,17 +2745,14 @@ 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 */
> - .byte 4,0x44 /* x16, 1 stopbit, no parity */
> +/* Initialisation table for SCC with 7.9872 MHz PCLK */
> +L(scc_initable_atari):
> + .byte 4,0x04 /* x1, 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 */
> + .byte 12,102,13,0 /* 38400 baud */
> .byte 14,2,14,3 /* use master clock for BRG, enable */
> .byte 3,0xc1 /* enable receiver */
> .byte 5,0xea /* enable transmitter */
> @@ -2800,7 +2798,7 @@ 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 +2808,7 @@ 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 +2844,21 @@ 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 +3027,7 @@ 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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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [RFC 4/4] m68k/atari: fix SCC initialization for debug console
2014-03-04 0:34 ` Michael Schmitz
@ 2014-03-04 2:31 ` Finn Thain
0 siblings, 0 replies; 3+ messages in thread
From: Finn Thain @ 2014-03-04 2:31 UTC (permalink / raw)
To: Michael Schmitz; +Cc: linux-m68k
On Tue, 4 Mar 2014, Michael Schmitz wrote:
> >
> > The 7.9872 MHz PCLK used in this patch was inferred from the existing
> > code as I don't have any hardware data.
>
> The difference in clock source settings is the main reason we can't use
> the exact same code IIRC.
> > .byte 14,2,14,3 /* use master clock for BRG, enable */
This is the other difference. For some reason the SCC initialization code
on a Mac selects the external clock for the Baud Rate Generator, whereas
on an Atari the master clock is used.
pmac_zilog does the same as the Mac code here. There is some mention of
MIDI in the comments there. AppleTalk also uses an external clock, IIRC.
I've no idea whether the master clock runs at the same rate across all Mac
models. Anyway, the existing code works on all the Macs I've tested
(though it needs the bootloader to "warm up serial ports" on some
powerbooks).
Finn
^ permalink raw reply [flat|nested] 3+ messages in thread
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2014-03-02 23:56 [RFC 4/4] m68k/atari: fix SCC initialization for debug console Finn Thain
2014-03-04 0:34 ` Michael Schmitz
2014-03-04 2:31 ` Finn Thain
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