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Implement whole-buffer write semihosting (#1013)

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* Implement whole-buffer write semihosting

Each semihosting call is very slow, so doing it for each character
does not provide an ideal developer experience.

This change allows the entire buffer to be printed out in a single call.
This commit is contained in:
Flaviu Tamas 2022-09-12 14:20:30 -04:00 committed by GitHub
parent a4ec3c4848
commit 5e9eb27ac2
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GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 26 additions and 24 deletions
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src/rp2_common/pico_stdio_semihosting/stdio_semihosting.c
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@ -8,31 +8,33 @@
#include "pico/stdio_semihosting.h"
#include "pico/binary_info.h"
//static void __attribute__((naked)) semihosting_puts(const char *s) {
// __asm (
//
// "mov r1, r0\n"
// "mov r0, #4\n"
// "bkpt 0xab\n"
// "bx lr\n"
// );
//}
static void __attribute__((naked)) semihosting_putc(__unused const char *c) {
__asm (
"mov r1, r0\n"
"mov r0, #3\n"
"bkpt 0xab\n"
"bx lr\n"
);
}
static void stdio_semihosting_out_chars(const char *buf, int length) {
for (int i = 0; i < length; i++) {
semihosting_putc(&buf[i]);
}
// must be volatile or the buffer gets put in registers & optimized away
volatile struct {
// https://developer.arm.com/documentation/dui0375/g/What-is-Semihosting-/SYS-WRITE--0x05-
// arguments, in order:
// word 0 = file handle (1 = stdout)
// word 1 = pointer to buffer
// word 2 = length of buffer
size_t fd;
const char *buf;
size_t len;
} args;
args.fd = 1; // 1 = stdout
args.buf = buf;
args.len = length;
__asm (
// r1 must contain a pointer to the arguments
"mov r1, %[args]\n"
// semihosting call number 0x05 = SYS_WRITE
"mov r0, #5\n"
// make the semihosting call: https://developer.arm.com/documentation/dui0375/g/What-is-Semihosting-/The-semihosting-interface
"bkpt 0xab\n"
:
: [args] "r" (&args)
: "r0", "r1");
}
stdio_driver_t stdio_semihosting = {