Espressif ESP32-S2 Programming Manual page 662

Chapter 2. API Reference
Name Description
WRBUF Write buffer
RDBUF Read buffer
WRDMA Write DMA
RDDMA Read DMA
SEG_DONE Segments done
ENQPI Enter QPI mode
WR_DONE Write
done
CMD8 Interrupt
CMD9 Interrupt
CMDA Interrupt
EXQPI Exit QPI mode
Moreover, WRBUF, RDBUF, WRDMA, RDDMA commands have their 2-bit and 4-bit version. To do transactions
in 2-bit or 4-bit mode, send the original command ORed by the corresponding command mask below. For example,
command 0xA1 means WRBUF in QIO mode.
Segment Transaction Mode
now. In this mode, for a transaction the slave load onto the DMA, the master is allowed to read or write in segments.
This way the master doesn't have to prepare large buffer as the size of data provided by the slave. After the master
finish reading/writing a buffer, it has to send corresponding termination command to the slave as a synchronization
signal. The slave driver will update new data (if exist) onto the DMA upon seeing the termination command.
The termination command is WR_DONE (0x07) for the WRDMA, and CMD8 (0x08) for the RDDMA.
Here's an example for the flow the master read data from the slave DMA:
1. The slave loads 4092 bytes of data onto the RDDMA
2. The master do seven RDDMA transactions, each of them are 512 bytes long, and reads the first 3584 bytes
from the slave
Espressif Systems
Command
0x01
0x02
0x03
0x04
0x05
0x06
segments 0x07
0x08
0x09
0x0A
0xDD
Mode
1-bit
DOUT
DIO
QOUT
QIO
QPI
Segment transaction mode is the only mode supported by the SPI Slave HD driver for
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Address
Buf addr
Buf addr
8 bits
8 bits
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Mask
0x00
0x10
0x50
0x20
0xA0
0xA0
Data
master to slave, no
longer than buffer
size
slave to master, no
longer than buffer
size
master to slave, no
longer than length
provided by slave
slave to master, no
longer than length
provided by slave
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Release v4.4