py: Overhaul and simplify printf/pfenv mechanism.

Previous to this patch the printing mechanism was a bit of a tangled
mess.  This patch attempts to consolidate printing into one interface.

All (non-debug) printing now uses the mp_print* family of functions,
mainly mp_printf.  All these functions take an mp_print_t structure as
their first argument, and this structure defines the printing backend
through the "print_strn" function of said structure.

Printing from the uPy core can reach the platform-defined print code via
two paths: either through mp_sys_stdout_obj (defined pert port) in
conjunction with mp_stream_write; or through the mp_plat_print structure
which uses the MP_PLAT_PRINT_STRN macro to define how string are printed
on the platform.  The former is only used when MICROPY_PY_IO is defined.

With this new scheme printing is generally more efficient (less layers
to go through, less arguments to pass), and, given an mp_print_t*
structure, one can call mp_print_str for efficiency instead of
mp_printf("%s", ...).  Code size is also reduced by around 200 bytes on
Thumb2 archs.

1 files changed, 3 insertions, 2 deletions

diff --git a/extmod/modujson.c b/extmod/modujson.c
index 747a86ac6a..d6095cbb8b 100644
--- a/extmod/modujson.c
+++ b/extmod/modujson.c
@@ -35,8 +35,9 @@
 
 STATIC mp_obj_t mod_ujson_dumps(mp_obj_t obj) {
     vstr_t vstr;
-    vstr_init(&vstr, 8);
-    mp_obj_print_helper((void (*)(void *env, const char *fmt, ...))vstr_printf, &vstr, obj, PRINT_JSON);
+    mp_print_t print;
+    vstr_init_print(&vstr, 8, &print);
+    mp_obj_print_helper(&print, obj, PRINT_JSON);
     return mp_obj_new_str_from_vstr(&mp_type_str, &vstr);
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_1(mod_ujson_dumps_obj, mod_ujson_dumps);