GPIO05 <\/td> UART RX<\/td> Input<\/td> GPIO19<\/td><\/tr><\/tbody><\/table><\/figure>\n<\/div>\n<\/div>\n<\/div>\n<\/details>\n\n\n\nOne very common mistake when doing prototyping is to forget to have a common ground between to active part dialoging via GPIO wire. In spent a few hours to understand this very obvious statement. The RP2350 and the ESP32 need to have a common ground do not forget it. <\/p>\n\n\n\n
The pin setup on the Pico can be changed very easily, however one needs to follow the at least the available UART \/ SPI0 & SPI1 schemes. This is the same for the ESP32, for my need I changed the GPIO setup in the firmware sdkconfig file. You can check the proper ESP32 pin configuration during the boot upon the firmware using the UART terminal connexion with log level information.<\/p>\n\n\n\n<\/p>\n\n\n\n
Now lets start the software integration<\/strong><\/p>\n\n\n\nSoftware integration<\/h2>\n\n\n\n The project source code is available on GitHub here, <\/p>\n\n\n\n
The following capabilities has been developed:<\/p>\n\n\n\n
\nSPI Communication<\/li>\n\n\n\n WiFi Module Init<\/li>\n\n\n\n WiFi Connexion \/ Disconnexion<\/li>\n\n\n\n LWIP stack integration<\/li>\n\n\n\n ESP32 Reset & Firmware update. <\/li>\n<\/ul>\n\n\n\nThe project structure is the following:<\/p>\n\n\n\n
``` The Typical End to End process flow from Boot to use of LWIP:<\/p>\n\n\n\n
\nStep 1: Setup the GPIO configuration for Data Ready and Handshake,<\/li>\n\n\n\n Step 2: Init the SPI communication protocol,<\/li>\n\n\n\n Step 3: Reset the ESP32,<\/li>\n\n\n\n Step 4: Handshake with the ESP32,<\/li>\n\n\n\n Step 5: Configure the WiFi,<\/li>\n\n\n\n Step 6: Init the Wifi Module,<\/li>\n\n\n\n Step 7: Connect Wifi,<\/li>\n\n\n\n Step 8: Enable the LWIP Stack,<\/li>\n\n\n\n Step 9: use Data.<\/li>\n<\/ul>\n\n\n\nStep 1: Setup the GPIO configuration<\/strong><\/p>\n\n\n\nThe function to configure the GPIO is located in esp32_control.h<\/p>\n\n\n\n
void esp32_control_init(void);<\/code><\/pre>\n\n\n\nIt will configure the following GPIO (Direction, level):<\/p>\n\n\n\n
\nBOOT (BOOT MODE)<\/li>\n\n\n\n EN (RESET)<\/li>\n\n\n\n HANDSHAKE<\/li>\n\n\n\n DATA READY<\/li>\n<\/ul>\n\n\n\nThe pin assignments are available in pin_config.h<\/p>\n\n\n\n
Step 2: Init the SPI Communication Protocol<\/strong><\/p>\n\n\n\nThe function to init SPI is located in esp32_spi.c :<\/p>\n\n\n\n
void esp32_spi_init(void);<\/code><\/pre>\n\n\n\nit uses the followings define in pin_config.h<\/p>\n\n\n\n
#define ESP32_SPI_INSTANCE spi1\n#define ESP32_SPI_MISO 8 \/\/ RX ESP32 GPIO05\n#define ESP32_SPI_MOSI 11 \/\/ TX ESP2 GPIO02\n#define ESP32_SPI_SCK 10 \/\/ CLK ESP32 GPIO06\n#define ESP32_SPI_CS 9 \/\/ CS ESP32 GPIO10<\/code><\/pre>\n\n\n\nbut also: <\/p>\n\n\n\n
#define ESP32_SPI_BAUDRATE (25 * 1000 * 1000) \/<\/code><\/pre>\n\n\n\nthe SPI mode is 3, and after doing test on a breadboard, 25 Mhz for SPI clock frequency works perfectly, and using the clean pcb, one should be able to increase the speed to 40 MHz and thus the overall throughput of the solution <\/p>\n\n\n\n
Step 3: Reset the ESP32<\/strong><\/p>\n\n\n\nThis step is of course not mandatory is you have already triggered a connexion to the ESP32.<\/p>\n\n\n\n
The reset function is located in esp32_control.c:<\/p>\n\n\n\n
void esp32_reset(void);<\/code><\/pre>\n\n\n\nIt will simply toggle the EN pin for a few milliseconds to trigger a reset of the ESP32.<\/p>\n\n\n\n
Step 4: Handshake with the ESP32<\/strong><\/p>\n\n\n\nThis is were the complexity starts, but it will be sorted out diligently;)<\/p>\n\n\n\n
The ESP32 is sending 2 type of Information:<\/p>\n\n\n\n
\nControl packet,<\/li>\n\n\n\n Data packet<\/li>\n<\/ul>\n\n\n\nControl packet are used to send event from the ESP32 to the PICO (Init, Configuration Success, Connect , Disconnect,…)<\/p>\n\n\n\n
Data packet are regular TCP\/IP data packets<\/p>\n\n\n\n
Just right after the RESET, the ESP32 send a control packet called INIT and the Master (RP2350\/RP2040) should capture it when Data Ready is HIGH and when Handshake is HIGH (both active High signal). <\/p>\n\n\n\n
Both Control packet & Data packet processing is managed by a central function through 2 circular buffers.<\/p>\n\n\n\n
The central function is driven by HANDSHAKE & DATA READY ISR located in esp32_control.c<\/p>\n\n\n\n
static void data_ready_irq_handler(uint gpio, uint32_t events);<\/code><\/pre>\n\n\n\nThis Interrupt function will monitor both EDGE RISE of HANDSHAKE & DATA READY. <\/p>\n\n\n\n
Packet are process via the callback function defined during the INIT process located in esp32_control.c:<\/p>\n\n\n\n
void esp32_set_packet_callback(void (*callback)(void));<\/code><\/pre>\n\n\n\nThe callback is defined by:<\/p>\n\n\n\n
esp32_set_packet_callback(&process_packets_immediate);<\/code><\/pre>\n\n\n\nThe function process_packets_immediate defined is main.c<\/p>\n\n\n\n
it will process by batch of 5 packets message queue to avoid the ISR blocking too long using the function defined in esp_hosted_mcu_control.c<\/p>\n\n\n\n
esp_hosted_mcu_process_packets()<\/code><\/pre>\n\n\n\nIt will manage the split of packet according to the type control \/ data<\/p>\n\n\n\n
Here we are looking for INIT packet to be sent to the control packet queue. <\/p>\n\n\n\n
control_packet_enqueue(&g_control_queue, &rx_header, rx_payload, len);<\/code><\/pre>\n\n\n\nThe function located in esp_hosted_mcu_control.c is in charge of handshake execution:<\/p>\n\n\n\n
bool esp_hosted_mcu_handshake(void);<\/code><\/pre>\n\n\n\nStep 5: Init the WiFi<\/strong><\/p>\n\n\n\nThe following sequence of code is needed to be done to init the WiFi<\/p>\n\n\n\n
printf("Initializing WiFi...\\n");\n if (!esp_hosted_rpc_wifi_init()) {\n printf("\u2717 WiFi init failed\\n");\n return;\n }\n esp32_state=ESP32_STATE_WIFI_INIT;\n\n \/\/ Set WiFi mode to STA\n printf("Setting WiFi mode to STA...\\n");\n if (!esp_hosted_rpc_set_wifi_mode(1)) { \/\/ 1 = WIFI_MODE_STA\n printf("\u2717 Failed to set WiFi mode\\n");\n return;\n }\n \n \/\/ Start WiFi \n printf("Starting WiFi...\\n");\n if (!esp_hosted_rpc_wifi_start()) {\n printf("\u2717 WiFi start failed\\n");\n return;\n }<\/code><\/pre>\n\n\n\nStep 6: Configure the Wifi <\/strong><\/p>\n\n\n\n\nprintf("\\nConfiguring WiFi credentials...\\n");\n \n \/\/ WiFi should already be initialized and started by handle_mcu_test() at boot\n \/\/ Just configure credentials and connect\n \n rpc_wifi_config_t config;\n memset(&config, 0, sizeof(config));\n \n const char *ssid = "SSID";\n const char *password = "PASSWORD";\n \n strncpy(config.ssid, ssid, sizeof(config.ssid) - 1);\n strncpy(config.password, password, sizeof(config.password) - 1);\n \n \/\/ Update status: connecting\n wifi_status_set_connecting(config.ssid);\n \n printf("Setting WiFi config for '%s'...\\n", config.ssid);\n if (!esp_hosted_rpc_set_wifi_config(&config)) {\n printf("\u2717 Failed to set WiFi config\\n");\n return;\n }\n printf("\u2713 WiFi config set\\n");\n \n \/\/ Brief delay for config processing\n sleep_ms(500);<\/code><\/pre>\n\n\n\nStep 7 Connect to the WiFi<\/strong><\/p>\n\n\n\n\n printf("\\nConnecting to '%s'...\\n", config.ssid);\n if (esp_hosted_rpc_wifi_connect()) {\n \/\/ WiFi connect returns true if request succeeded, but doesn't guarantee connection\n \/\/ Wait for connection to complete with retries\n wifi_ap_record_t ap_info;\n bool connected = false;\n bool connection_failed = false;\n bool seen_connect_event = false;\n \n printf("Waiting for WiFi connection to complete");\n for (int attempt = 0; attempt < 30; attempt++) { \/\/ 30 seconds timeout (1s per attempt)\n printf(".");\n fflush(stdout);\n sleep_ms(1000); \/\/ Wait 1 second between attempts\n \n \/\/ Process any RPC events (like disconnect events indicating auth failure)\n \/\/ This will call esp32_event_handler() for any pending events\n esp_hosted_mcu_process_queued_control_packets();\n \n \/\/ Check WiFi state machine\n wifi_status_singleton_t* status = wifi_status_get();\n \n \/\/ Debug: show current state\n if (attempt == 0 || status->connection_state != WIFI_STATE_CONNECTING) {\n printf("[state=%d:%s]\\n", status->connection_state, \n wifi_status_connection_state_str(status->connection_state));\n fflush(stdout);\n }\n \n \/\/ Track if we see a connect event\n if (status->connection_state == WIFI_STATE_CONNECTED) {\n seen_connect_event = true;\n }\n \n \/\/ Only treat disconnect as failure if:\n \/\/ 1. We've waited at least 3 seconds (allow handshake time)\n \/\/ 2. We either saw a connect event, or we're past second 5 with no connect\n if (status->connection_state == WIFI_STATE_DISCONNECTED && \n (attempt >= 3 || (attempt >= 5 && !seen_connect_event))) {\n \/\/ Connection was explicitly rejected by ESP32\n printf("\\n\u2717 WiFi connection failed with reason: %s\\n", \n wifi_status_disconnect_reason_str(status->disconnect_reason));\n connection_failed = true;\n break;\n }\n \n if (status->connection_state == WIFI_STATE_CONNECTED) {\n \/\/ Successfully connected - get AP info for display\n if (esp_hosted_rpc_wifi_sta_get_ap_info(&ap_info) && ap_info.ssid[0] != '\\0') {\n connected = true;\n break;\n }\n }\n }\n printf("\\n");\n \n if (connected) {\n \/\/ Connection verified - AP info has non-empty SSID matching our request\n printf("\u2713 Successfully connected to '%s'!\\n", config.ssid);\n \n wifi_status_set_connected(\n (char*)ap_info.ssid, \n ap_info.bssid,\n ap_info.channel,\n ap_info.rssi,\n ap_info.authmode\n );\n \n \/\/ Get network config and update status\n rpc_dhcp_status_t dhcp_status;\n if (esp_hosted_rpc_get_dhcp_status(&dhcp_status) && dhcp_status.dhcp_up) {\n wifi_status_update_network(\n dhcp_status.ip,\n dhcp_status.gateway,\n dhcp_status.netmask,\n dhcp_status.dns_up ? dhcp_status.dns : NULL\n );\n }\n \n esp32_state=ESP32_STATE_WIFI_CONNECTED;\n } else if (connection_failed) {\n \/\/ Connection was explicitly rejected by ESP32 (disconnect event received)\n printf("\u2717 Connection rejected by ESP32\\n");\n wifi_status_set_disconnected(WIFI_REASON_AUTH_FAIL);\n } else {\n \/\/ Connection timeout - stuck in CONNECTING state after 30 seconds\n \/\/ This usually indicates wrong password or network not responding\n printf("\u2717 Connection timeout after 30 seconds\\n");\n printf("WiFi remains in CONNECTING state - possible causes:\\n");\n printf(" - Incorrect SSID or password (most likely)\\n");\n printf(" - AP out of range\\n");\n printf(" - Network authentication issues\\n");\n printf(" - ESP32 WiFi not responding\\n");\n wifi_status_set_disconnected(WIFI_REASON_AUTH_FAIL);\n }<\/code><\/pre>\n\n\n\n<\/p>\n\n\n\n
To be continued with the performance running and outcome in part 2<\/p>\n\n\n\n
<\/p>\n","protected":false},"excerpt":{"rendered":"
As I continue my journey building stuff based on Raspberry CPU, for one project I need to build a custom RP2350 board and to onboard on the PCB a WiFi Module. Here is the source of the project on GitHub https:\/\/github.com\/vibr77\/ESP32C3_RP2350_WiFi One could argue that using the recent release of the RM2 (existing on PICOW […]<\/p>\n","protected":false},"author":1,"featured_media":377,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[31],"tags":[],"class_list":["post-334","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-experiment"],"jetpack_featured_media_url":"https:\/\/www.r3tr0.net\/wp-content\/uploads\/2026\/01\/IMG_0762-Large-e1768377490363.jpeg","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.r3tr0.net\/index.php\/wp-json\/wp\/v2\/posts\/334","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.r3tr0.net\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.r3tr0.net\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.r3tr0.net\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.r3tr0.net\/index.php\/wp-json\/wp\/v2\/comments?post=334"}],"version-history":[{"count":26,"href":"https:\/\/www.r3tr0.net\/index.php\/wp-json\/wp\/v2\/posts\/334\/revisions"}],"predecessor-version":[{"id":384,"href":"https:\/\/www.r3tr0.net\/index.php\/wp-json\/wp\/v2\/posts\/334\/revisions\/384"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.r3tr0.net\/index.php\/wp-json\/wp\/v2\/media\/377"}],"wp:attachment":[{"href":"https:\/\/www.r3tr0.net\/index.php\/wp-json\/wp\/v2\/media?parent=334"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.r3tr0.net\/index.php\/wp-json\/wp\/v2\/categories?post=334"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.r3tr0.net\/index.php\/wp-json\/wp\/v2\/tags?post=334"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
![\"\"](\"https:\/\/www.r3tr0.net\/wp-content\/uploads\/2026\/01\/ESP32C3.jpeg\")
<\/figure>\n\n\n\n![\"\"](\"https:\/\/www.r3tr0.net\/wp-content\/uploads\/2026\/01\/IMG_0762-Large-e1768377490363-1024x592.jpeg\")
<\/figure>\n\n\n\n![\"\"](\"https:\/\/www.r3tr0.net\/wp-content\/uploads\/2026\/01\/RaspberryPicoPinput-1024x677.png\")
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