extmod/network_ppp_lwip: Add network.PPP via lwIP.

This commit adds a new `network.PPP` interface which works on any port that
has bare-metal lwIP, eg rp2, stm32, mimxrt.

It has been tested on stm32.  A board needs to enable
`MICROPY_PY_NETWORK_PPP_LWIP` and then it can use it as follows:

    import network

    ppp = network.PPP(uart)
    ppp.connect()

    while not ppp.isconnected():
        pass

    # use `socket` module as usual, etc

    ppp.disconnect()

Usually the application must first configure the cellular/etc UART link to
get it connected and in to PPP mode first (eg ATD*99#), before handing over
control to `network.PPP`.

The PPP interface automatically configures the UART IRQ callback to call
PPP.poll() on incoming data.
Signed-off-by: Damien George <damien@micropython.org>

extmod/extmod.cmake

@@ -49,6 +49,7 @@ set(MICROPY_SOURCE_EXTMOD
     ${MICROPY_EXTMOD_DIR}/network_cyw43.c
     ${MICROPY_EXTMOD_DIR}/network_lwip.c
     ${MICROPY_EXTMOD_DIR}/network_ninaw10.c
+    ${MICROPY_EXTMOD_DIR}/network_ppp_lwip.c
     ${MICROPY_EXTMOD_DIR}/network_wiznet5k.c
     ${MICROPY_EXTMOD_DIR}/os_dupterm.c
     ${MICROPY_EXTMOD_DIR}/vfs.c
@@ -313,6 +314,32 @@ if(MICROPY_PY_LWIP)
         ${MICROPY_LIB_LWIP_DIR}/core/timeouts.c
         ${MICROPY_LIB_LWIP_DIR}/core/udp.c
         ${MICROPY_LIB_LWIP_DIR}/netif/ethernet.c
+        ${MICROPY_LIB_LWIP_DIR}/netif/ppp/auth.c
+        ${MICROPY_LIB_LWIP_DIR}/netif/ppp/ccp.c
+        ${MICROPY_LIB_LWIP_DIR}/netif/ppp/chap-md5.c
+        ${MICROPY_LIB_LWIP_DIR}/netif/ppp/chap_ms.c
+        ${MICROPY_LIB_LWIP_DIR}/netif/ppp/chap-new.c
+        ${MICROPY_LIB_LWIP_DIR}/netif/ppp/demand.c
+        ${MICROPY_LIB_LWIP_DIR}/netif/ppp/eap.c
+        ${MICROPY_LIB_LWIP_DIR}/netif/ppp/ecp.c
+        ${MICROPY_LIB_LWIP_DIR}/netif/ppp/eui64.c
+        ${MICROPY_LIB_LWIP_DIR}/netif/ppp/fsm.c
+        ${MICROPY_LIB_LWIP_DIR}/netif/ppp/ipcp.c
+        ${MICROPY_LIB_LWIP_DIR}/netif/ppp/ipv6cp.c
+        ${MICROPY_LIB_LWIP_DIR}/netif/ppp/lcp.c
+        ${MICROPY_LIB_LWIP_DIR}/netif/ppp/magic.c
+        ${MICROPY_LIB_LWIP_DIR}/netif/ppp/mppe.c
+        ${MICROPY_LIB_LWIP_DIR}/netif/ppp/multilink.c
+        ${MICROPY_LIB_LWIP_DIR}/netif/ppp/polarssl/md5.c
+        ${MICROPY_LIB_LWIP_DIR}/netif/ppp/pppapi.c
+        ${MICROPY_LIB_LWIP_DIR}/netif/ppp/ppp.c
+        ${MICROPY_LIB_LWIP_DIR}/netif/ppp/pppcrypt.c
+        ${MICROPY_LIB_LWIP_DIR}/netif/ppp/pppoe.c
+        ${MICROPY_LIB_LWIP_DIR}/netif/ppp/pppol2tp.c
+        ${MICROPY_LIB_LWIP_DIR}/netif/ppp/pppos.c
+        ${MICROPY_LIB_LWIP_DIR}/netif/ppp/upap.c
+        ${MICROPY_LIB_LWIP_DIR}/netif/ppp/utils.c
+        ${MICROPY_LIB_LWIP_DIR}/netif/ppp/vj.c
     )
 
     list(APPEND MICROPY_INC_CORE

extmod/extmod.mk

@@ -51,6 +51,7 @@ SRC_EXTMOD_C += \
 	extmod/network_esp_hosted.c \
 	extmod/network_lwip.c \
 	extmod/network_ninaw10.c \
+	extmod/network_ppp_lwip.c \
 	extmod/network_wiznet5k.c \
 	extmod/os_dupterm.c \
 	extmod/vfs.c \
@@ -370,6 +371,32 @@ SRC_THIRDPARTY_C += $(addprefix $(LWIP_DIR)/,\
 	core/ipv6/mld6.c \
 	core/ipv6/nd6.c \
 	netif/ethernet.c \
+	netif/ppp/auth.c \
+	netif/ppp/ccp.c \
+	netif/ppp/chap-md5.c \
+	netif/ppp/chap_ms.c \
+	netif/ppp/chap-new.c \
+	netif/ppp/demand.c \
+	netif/ppp/eap.c \
+	netif/ppp/ecp.c \
+	netif/ppp/eui64.c \
+	netif/ppp/fsm.c \
+	netif/ppp/ipcp.c \
+	netif/ppp/ipv6cp.c \
+	netif/ppp/lcp.c \
+	netif/ppp/magic.c \
+	netif/ppp/mppe.c \
+	netif/ppp/multilink.c \
+	netif/ppp/polarssl/md5.c \
+	netif/ppp/pppapi.c \
+	netif/ppp/ppp.c \
+	netif/ppp/pppcrypt.c \
+	netif/ppp/pppoe.c \
+	netif/ppp/pppol2tp.c \
+	netif/ppp/pppos.c \
+	netif/ppp/upap.c \
+	netif/ppp/utils.c \
+	netif/ppp/vj.c \
 	)
 ifeq ($(MICROPY_PY_LWIP_LOOPBACK),1)
 CFLAGS_EXTMOD += -DLWIP_NETIF_LOOPBACK=1

extmod/modnetwork.c

@@ -156,6 +156,10 @@ static const mp_rom_map_elem_t mp_module_network_globals_table[] = {
     { MP_ROM_QSTR(MP_QSTR_ipconfig), MP_ROM_PTR(&mod_network_ipconfig_obj) },
     #endif
 
+    #if MICROPY_PY_NETWORK_PPP_LWIP
+    { MP_ROM_QSTR(MP_QSTR_PPP), MP_ROM_PTR(&mp_network_ppp_lwip_type) },
+    #endif
+
     // Defined per port in mpconfigport.h
     #ifdef MICROPY_PORT_NETWORK_INTERFACES
     { MP_ROM_QSTR(MP_QSTR_route), MP_ROM_PTR(&network_route_obj) },

extmod/modnetwork.h

@@ -72,6 +72,10 @@ mp_obj_t mod_network_hostname(size_t n_args, const mp_obj_t *args);
 
 #include "lwip/init.h"
 
+#if MICROPY_PY_NETWORK_PPP_LWIP
+extern const struct _mp_obj_type_t mp_network_ppp_lwip_type;
+#endif
+
 struct netif;
 void mod_network_lwip_init(void);
 void mod_network_lwip_poll_wrapper(uint32_t ticks_ms);