SPI Device HWIP Technical Specification



SPI Generic Mode

  • Single-bit wide SPI device interface implementing a raw data transfer protocol termed “Firmware Operation Mode”
    • No address bits, data is sent and received from peripheral pins to/from an internal buffer
    • Intended to be used to bulk-load data into and out of the chip
    • Not intended to support EEPROM or other addressing modes (functionality to come in later versions)
  • Supports clock polarity and reverse bit order configurations
  • Flexible RX/TX Buffer size within an SRAM range
  • Interrupts for RX/TX SRAM FIFO conditions (empty, full, designated level for RX, TX)

SPI Flash/ Passthrough Modes

  • Support Serial Flash emulation
    • HW processed Read Status, Read JEDEC ID, Read SFDP, EN4B/ EX4B, and multiple read commands
    • 16 depth Command/ Address FIFOs and 256B Payload buffer for command upload
    • 2x 1kB read buffer for read commands
    • 1kB mailbox buffer and configurable mailbox target address
  • Support SPI passthrough
    • Filtering of inadmissible commands (256-bit filter CSR)
    • Address translation for read commands
    • First 4B payload translation
    • HW control of SPI PADs’ output enable based on command information list
    • SW configurable internal command process for Read Status, Read JEDEC ID, Read SFDP, and read access to the mailbox space
    • Targets 33MHz @ Quad read mode, fall backs to 25MHz
  • Automated tracking of 3B/ 4B address mode in the flash and passthrough modes
  • 24 entries of command information slots
    • Configurable address/ dummy/ payload size per opcode

TPM over SPI

  • In compliance with TPM PC Client Platform
  • up to 64B compile-time configurable read and write data buffer (default: 4B)
  • 1 TPM command (8b) and 1 address (24bit) buffer
  • HW controlled wait state
  • Shared SPI with other SPI Device functionalities. Unique CS# for the TPM
    • Flash or Passthrough mode can be active with TPM mode. Generic and TPM modes are mutually exclusive.
  • HW processed registers for read requests during FIFO mode
    • TPM_HASH_START returns FFh
  • 5 Locality (compile-time parameter)


The SPI device module consists of four functions, the generic mode, SPI Flash mode, SPI passthrough mode, and TPM over SPI mode.

The SPI generic mode is a serial-to-parallel receive (RX) and parallel-to-serial transmit (TX) full duplex design (single line mode) used to communicate with an outside host. This first version of the module supports operations controlled by firmware to dump incoming single-line RX data (SDI) to an internal RX buffer, and send data from a transmit buffer to single-line TX output (SDO). The clock for the peripheral data transfer uses the SPI peripheral pin SCK. In this design the SCK is directly used to drive the interface logic as its primary clock, which has performance benefits, but incurs design complications described later.

The SW can receive TPM commands with payload (address and data) and respond to the read commands with the return data using the TPM submodule in the SPI_DEVICE HWIP. The submodule provides the command, address, write, and read FIFOs for the SW to communicate with the TPM host system. The submodule also supports the SW by managing a certain set of the FIFO registers and returning the read request by HW quickly.

In Flash mode, SPI Device HWIP behaves as a Serial Flash device by recognizing SPI Flash commands and processing those commands by HW. The commands processed by HW are Read Status (1, 2, 3), Read JEDEC ID, Read SFDP, EN4B/ EX4B, and read commands with aid of SW. The IP supports Normal Read, Fast Read, Fast Read Dual Output, Fast Read Quad Output. This version of IP does not support Dual IO, Quad IO, QPI commands.

In Passthrough mode, SPI Device receives SPI transactions from a host system and forwards the transactions to a downstream flash device. SW may filter prohibited commands by configuring 256-bit FILTER CSR. The IP cancels ongoing transaction if the received opcode matches to the filter CSR by de-asserting CSb and gating SCK to the downstream flash device.

SW may program CSRs to change the address and/or the first 4 bytes of payload on-the-fly in Passthrough mode. The address translation feature allows SW to maintain A/B binary images without aids of the host system. The payload translation may be used to change the payload of Write Status commands to not allow certain fields to be modified.

In Passthrough mode, parts of the Flash modules can be active. While in Passthrough mode, SW may configure the IP to process certain commands internally. SW is recommended to filter the commands being processed internally. Mailbox is an exception as it shares the Read command opcode.

SPI Device Modes and Active Submodules

SPI Device HWIP has three modes + TPM mode, which are “Generic” mode (also known as FwMode), “Flash” mode, and “Passthrough” mode. Generic mode is exclusive. Flash and Passthrough modes share many parts of the datapath. TPM mode only shares the SPI and has separate CSb port, which allows that the host sends TPM commands while other SPI mode is active (except Generic mode).




The SPI device supports emulating an EEPROM (SPI flash mode in this document). The TPM submodule conforms to the TPM over SPI 2.0 specification. The TPM operation follows TCG PC Client Platform TPM Profile Specification Section 7.