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realtek: rt-loader bootbase device enhancement

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Until now the rt-loader only works on U-Boot driven devices where the
environment (e.g. coprocessor) is usually setup properly. Devices like
the ZyXEL GS1920 series use BootBase as start environment and skip
some of the basic initialization steps. rt-loader will fail in these
cases. Take care about the CP0 registers.

Additionally enhance the documentation of the printf implementation.
It was optimized during the different revisions of the initial PR.

Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>
Link: https://github.com/openwrt/openwrt/pull/19253
Signed-off-by: Robert Marko <robimarko@gmail.com>
This commit is contained in:
Markus Stockhausen 2025-06-28 11:39:27 -04:00 committed by Robert Marko
parent 5d0a07c90f
commit 978d24ce40
4 changed files with 29 additions and 5 deletions
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7
target/linux/realtek/image/rt-loader/include/globals.h
View file

@ -11,6 +11,13 @@
#define HEAP_SIZE 0x40000
#define MEMORY_ALIGNMENT 32
#define CP0_COUNT $9
#define CP0_COMPARE $11
#define CP0_STATUS $12
#define CP0_CAUSE $13
#define CP0_WATCHLO $18
#define CP0_WATCHHI $19
#define printf(fmt, ...) npf_pprintf(board_putchar, NULL, fmt, ##__VA_ARGS__)
#define snprintf npf_snprintf

6
target/linux/realtek/image/rt-loader/src/board.c
View file

@ -21,10 +21,8 @@
#define RTL93XX_CHIP_INFO_EN 0xa0000
/*
* board_putchar() is the central function to write to serial console of the device. Some printf
* libraries (e.g. https://github.com/mpaland/printf) need a fixed function name like _putchar.
* To keep the original library as is, link the two functions with gcc compiler option
* -D_putchar=board_putchar
* board_putchar() is the central function to write to serial console of the device. This is
* linked to printf() and the provider library via globals.h.
*/
void board_putchar(int ch, void *ctx)

2
target/linux/realtek/image/rt-loader/src/main.c
View file

@ -69,7 +69,7 @@ void welcome(void)
board_get_system(system, sizeof(system));
printf("rt-loader\n");
printf("\nrt-loader\n");
printf("Running on %s with %dMB\n", system, board_get_memory() >> 20);
}

19
target/linux/realtek/image/rt-loader/src/startup.S
View file

@ -14,6 +14,10 @@
add \reg, $t9
.endm
.macro _EHB
sll $zero, 3
.endm
.section .text
.globl _start
.ent _start
@ -28,6 +32,21 @@ _where_am_i:
move $t9, $ra
subu $t9, $t9, 0x8
# This loader might be run in environments that are not properly initialized - e.g. ZyXEL
# devices with BootBase loader. Be careful and setup the coprocessor registers.
mtc0 $zero, CP0_WATCHLO
mtc0 $zero, CP0_WATCHHI
mtc0 $zero, CP0_CAUSE
mfc0 $t0, CP0_STATUS
li $t1, 0x1000001f
or $t0, $t1
xori $t0, 0x1f
mtc0 $t0, CP0_STATUS
_EHB
mtc0 $zero, CP0_COUNT
mtc0 $zero, CP0_COMPARE
_EHB
# Check if this our first run (_kernel_load_addr = 0?)