Espressif ESP32-S2 User Manual

Chapter 4. API Guides
4.19.8 DMA Buffer in the stack
Placing DMA buffers in the stack is possible but discouraged. If doing so, pay attention to the following:
• Placing DRAM buffers on the stack is not recommended if the stack may be in PSRAM. If the stack of a task
is placed in the PSRAM, several steps have to be taken as described in Support for external RAM.
• Use macro WORD_ALIGNED_ATTR in functions before variables to place them in proper positions like:
void app_main()
{
uint8_t stuff;
WORD_ALIGNED_ATTR uint8_t buffer[] = "I want to send something"; //or␣
,→the buffer will be placed right after stuff.
// initialization code...
spi_transaction_t temp = {
.tx_buffer = buffer,
.length = 8 * sizeof(buffer),
};
spi_device_transmit(spi, &temp);
// other stuff
}
4.20 lwIP
ESP-IDF uses the open source lwIP lightweight TCP/IP stack. The ESP-IDF version of lwIP (esp-lwip) has some
modifications and additions compared to the upstream project.
4.20.1 Supported APIs
ESP-IDF supports the following lwIP TCP/IP stack functions:
• BSD Sockets API
• Netconn API is enabled but not officially supported for ESP-IDF applications
Adapted APIs
Some common lwIP “app”APIs are supported indirectly by ESP-IDF:
• DHCP Server & Client are supported indirectly via the ESP-NETIF functionality
• Simple Network Time Protocol (SNTP) is supported via the lwip/include/apps/sntp/sntp.h
lwip/lwip/src/include/lwip/apps/sntp.h functions (see also SNTP Time Synchronization)
• ICMP Ping is supported using a variation on the lwIP ping API. See ICMP Echo.
• NetBIOS lookup is available using the standard lwIP API. protocols/http_server/restful_server has an option
to demonstrate using NetBIOS to look up a host on the LAN.
• mDNS uses a different implementation to the lwIP default mDNS (see mDNS Service), but lwIP can look up
mDNS hosts using standard APIs such as gethostbyname() and the convention hostname.local,
provided the CONFIG_LWIP_DNS_SUPPORT_MDNS_QUERIES setting is enabled.
4.20.2 BSD Sockets API
The BSD Sockets API is a common cross-platform TCP/IP sockets API that originated in the Berkeley Standard
Distribution of UNIX but is now standardized in a section of the POSIX specification. BSD Sockets are sometimes
called POSIX Sockets or Berkeley Sockets.
As implemented in ESP-IDF, lwIP supports all of the common usages of the BSD Sockets API.
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Espressif ESP32-S2 Specifications

General

Brand	Espressif
Model	ESP32-S2
Category	Single board computers
Language	English