SPI Engine Instruction Set Specification#
The SPI Engine instruction set is a simple 16-bit instruction set of which 13-bits are currently allocated (bits 15,11,10 are always 0).
Instructions#
Transfer Instruction#
15 |
14 |
13 |
12 |
11 |
10 |
9 |
8 |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
0 |
0 |
0 |
0 |
0 |
0 |
r |
w |
n |
n |
n |
n |
n |
n |
n |
n |
The transfer instructions perform a low-level SPI transfer. It will generate SCLK transitions for the specified amount of cycles according to the SPI configuration register. If the r bit is set the SDI pin will be sampled and stored in the shift register at the end of each word the data is output on the SDI_DATA stream. If the w bit is set the SDO pin will be updated with the data received from the SDO_DATA stream. If the w bit is set the sdo_t signal will also be set to 0 for the duration of the transfer. If the SDI_DATA stream is not able to accept data or the SDO_DATA stream is not able to provide data the execution is stalled at the end/start of the transfer until data is accepted/becomes available.
Bits |
Name |
Description |
|---|---|---|
r |
Read |
If set to 1 data will be read from the SDI pin during and the read words will be available on the SDI_DATA interface. |
w |
Write |
If set to 1 data will be taken from the SDO_DATA interface and output on the SDO pin. |
n |
Length |
n + 1 number of words that will be transferred. |
Chip-Select Instruction#
15 |
14 |
13 |
12 |
11 |
10 |
9 |
8 |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
0 |
0 |
0 |
1 |
0 |
0 |
t |
t |
s |
s |
s |
s |
s |
s |
s |
s |
The chip-select instruction updates the value chip-select output signal of the SPI Engine execution module.
The physical outputs on each pin may be inverted relative to the command according to the mask set by CS Invert Mask Instruction. The Invert Mask acts only on the output registers of the Chip-Select pins. Thus, if the last 8 bits of the Chip-Select instruction are 0xFE, only CS[0] will be active regardless of polarity. The polarity inversion process (if needed) is transparent to the programmer.
Before and after the update is performed the execution module is paused for the specified delay. The length of the delay depends on the module clock frequency, the setting of the prescaler register and the parameter \(t\) of the instruction. This delay is inserted before and after the update of the chip-select signal, so the total execution time of the chip-select instruction is twice the delay, with an added fixed 2 clock cycles (fast clock, not prescaled) before for the internal logic.
Bits |
Name |
Description |
|---|---|---|
t |
Delay |
Delay before and after setting the new configuration. |
s |
Chip-select |
The new chip-select configuration. |
Configuration Write Instruction#
15 |
14 |
13 |
12 |
11 |
10 |
9 |
8 |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
0 |
0 |
1 |
0 |
0 |
0 |
r |
r |
v |
v |
v |
v |
v |
v |
v |
v |
The configuration writes instruction updates a Configuration Registers of the SPI Engine execution module with a new value.
Bits |
Name |
Description |
|---|---|---|
r |
Register |
Configuration register address. 2’b00 = Prescaler Configuration Register 2’b01 = SPI Configuration Register 2’b10 = Dynamic Transfer Length Register. |
v |
Value |
New value for the configuration register. |
Synchronize Instruction#
15 |
14 |
13 |
12 |
11 |
10 |
9 |
8 |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
0 |
0 |
1 |
1 |
0 |
0 |
0 |
0 |
n |
n |
n |
n |
n |
n |
n |
n |
The synchronize instruction generates a synchronization event on the SYNC output stream. This can be used to monitor the progress of the command stream. The synchronize instruction is also used by the SPI Engine Interconnect Module module to identify the end of a transaction and re-start the arbitration process.
Bits |
Name |
Description |
|---|---|---|
n |
id |
Value of the generated synchronization event. |
Sleep Instruction#
15 |
14 |
13 |
12 |
11 |
10 |
9 |
8 |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
0 |
0 |
1 |
1 |
0 |
0 |
0 |
1 |
t |
t |
t |
t |
t |
t |
t |
t |
The sleep instruction stops the execution of the command stream for the specified amount of time. The time is based on the external clock frequency the configuration value of the prescaler register and the time parameter of the instruction. A fixed delay of two clock cycles (fast, not affected by the prescaler) is the minimum, needed by the internal logic.
Bits |
Name |
Description |
|---|---|---|
t |
Time |
The amount of prescaler cycles to wait, minus one. |
CS Invert Mask Instruction#
15 |
14 |
13 |
12 |
11 |
10 |
9 |
8 |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
0 |
1 |
0 |
0 |
r |
r |
r |
r |
m |
m |
m |
m |
m |
m |
m |
m |
The CS Invert Mask Instructions allows the user to select on a per-pin basis whether the Chip Select will be active-low (default) or active-high (inverted). Note that the Chip-Select instructions should remain the same because the value of CS is inverted at the output register, and additional logic (e.g. reset counters) occurs when the CS active state is asserted.
Since the physical values on the pins are inverted at the output, the current Invert Mask does not affect the use of the Chip-Select Instruction. As an example, a Chip-Select Instruction with the ‘s’ field equal to 0xFE will always result in only CS[0] being active. For an Invert Mask of 0xFF, this would result on only CS[0] being high. For an Invert Mask of 0x00, this would result on only CS[0] being low. For an Invert Mask of 0x01, this would result on all CS pins being high, but only CS[0] is active in this case (since it’s the only one currently treated as active-high).
This was introduced in version 1.02.00 of the core.
Bits |
Name |
Description |
|---|---|---|
r |
reserved |
Reserved for future use. Must always be set to 0. |
m |
Mask |
Mask for selecting inverted CS channels. For the bits set to 1, the corresponding channel will be inverted at the output. |
Configuration Registers#
The SPI Engine execution module has a set of 8-bit configuration registers which can be used to dynamically modify the behavior of the module at runtime.
SPI Configuration Register#
The SPI configuration register configures various aspects of the low-level SPI bus behavior.
Bits |
Name |
Description |
|---|---|---|
[7:4] |
reserved |
Must always be 0. |
[3] |
sdo_idle_state |
Configures the output of the SDO pin when CS is inactive or during read-only transfers. |
[2] |
three_wire |
Configures the output of the three_wire pin. |
[1] |
CPOL |
Configures the polarity of the SCLK signal. When 0, the idle state of the SCLK signal is low. When 1, the idle state of the SCLK signal is high. |
[0] |
CPHA |
Configures the phase of the SCLK signal. When 0, data is sampled on the leading edge and updated on the trailing edge. When 1, data is sampled on the trailing edge and updated on the leading edge. |
Prescaler Configuration Register#
The prescaler configuration register configures the divider that is applied to the module clock when generating the SCLK signal and other internal control signals used by the sleep and chip-select commands.
Bits |
Name |
Description |
|---|---|---|
[7:0] |
div |
Prescaler clock divider |
The frequency of the SCLK signal is derived from the module clock frequency using the following formula:
If no prescaler block is present div is 0.
Dynamic Transfer Length Register#
The dynamic transfer length register sets the length (in bits) of a transfer. By default, the transfer length is equal to the DATA_WIDTH of the execution module. If required the user can reduce this length by setting this register. A general rule of thumb is to set the DATA_WIDTH parameter to the largest transfer length supported by the target device.
Bits |
Name |
Description |
|---|---|---|
[7:0] |
div |
Dynamic transfer length |