Espressif Systems ESP Faq page 96

Chapter 4. Software framework
When using ESP32 as an SPI Master device, how many bytes of data can be transfered at one time in non-
DMA mode?
• Up to 64 Bytes of data can be transferred at one time in such condition.
• When the transmitted data does not exceed 32 bits, you can use the 4-byte array in the SPI Master driver as
the buffer for data transmission. For details, please refer to
• But when the transmitted data exceeds 32 bits, you need to set the buffer for SPI data transmission by yourself.
For details, please refer to
• When using ESP32 as an SPI Master device to transmit more than 32 bits of SPI data in non-DMA mode,
please refer to the example lcd.
When using the ESP32-S3-WROOM-1 (ESP32-S3R2) module to enable its PSRAM configuration based on
the "hello-world"example in ESP-IDF v4.4, the following error is printed. What is the reason?
E (232) spiram: Virtual address not enough for PSRAM!
• ESP32-S3R2 chip integrates a 4-wire 2 MB PSRAM, please set PSRAM Mode to Quad mode in
menuconfig before your action as follows:
menuconfig > Component config > ESP32S3 Specific > Support for ex-
ternal, SPI connected RAM > SPI RAM config > Mode (QUAD/OCT) of SPI
RAM chip in use (Ouad Mode PSRAM)
When using the ESP32-S3-WROOM-2 (ESP32-S3R8V) module to enable the PSRAM configuration based
on the "hello-world"example in ESP-IDF v4.4, the following error is printed. What is the reason?
E (453) psrm: psrm ID read error: 0x00ffff
E (454) cpu start: Failed to init external RAM!
ESP32-S3R8V chip integrates a 8-wire 8 MB PSRAM, please set PSRAM mode to Octal mode in
menuconfig before your action as follows:
menuconfig > Component config > ESP32S3 Specific > Support for
external, SPI connected RAM > SPI RAM config > Mode (QUAD/OCT)
of SPI RAM chip in use (Octal Mode PSRAM)
Does ESP8266 RTOS SDK support full duplex for SPI?
CHIP: ESP8266
No, it doesn't. Because ESP8266 doesn't support DMA, in order to improve the transmission per-
formance, the entire FIFO is used. So it can only be half duplex. Please refer to
details.
Can ESP32 support 9-bit clock mode for 3-wire SPI (i.e. a mode where the first bit indicates whether the
next 8 bits are command or data)?
No. Currently, all ESP32 series chips does not support non-byte-aligned data transfer, i.e., only support
8-bit-aligned data tranfer. For details, please refer to
Newer versions of ESP32 series chips may support non-byte-aligned data transfer. However, there is no
specific schedule for this functionality.
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