103 lines
5.9 KiB
Plaintext
103 lines
5.9 KiB
Plaintext
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:sectnums:
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==== Serial Data Interface Controller (SDI)
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[cols="<3,<3,<4"]
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[frame="topbot",grid="none"]
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|=======================
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| Hardware source file(s): | neorv32_sdi.vhd |
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| Software driver file(s): | neorv32_sdi.c |
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| | neorv32_sdi.h |
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| Top entity port: | `sdi_clk_i` | 1-bit serial clock input
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| | `sdi_dat_o` | 1-bit serial data output
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| | `sdi_dat_i` | 1-bit serial data input
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| | `sdi_csn_i` | 1-bit chip-select input (low-active)
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| Configuration generics: | `IO_SDI_EN` | implement SDI controller when `true`
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| | `IO_SDI_FIFO` | data FIFO size, has to a power of two, min 1
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| CPU interrupts: | fast IRQ channel 11 | configurable SDI interrupt (see <<_processor_interrupts>>)
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|=======================
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**Overview**
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The serial data interface module provides a **device-class** SPI interface and allows to connect the processor
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to an external SPI _host_, which is responsible for triggering (clocking) the actual transmission - the SDI is entirely
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passive. An optional receive/transmit FIFO can be configured via the _IO_SDI_FIFO_ generic to support block-based
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transmissions without CPU interaction.
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.Device-Mode Only
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[NOTE]
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The NEORV32 SDI module only supports _device mode_. Transmission are initiated by an external host and not by the
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the processor itself. If you are looking for a _host-mode_ serial peripheral interface (transactions
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initiated by the NEORV32) check out the <<_serial_peripheral_interface_controller_spi>>.
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The SDI module provides a single control register `CTRL` to configure the module and to check it's status
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and a single data register `DATA` for receiving/transmitting data.
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**Theory of Operation**
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The SDI module is enabled by setting the `SDI_CTRL_EN` bit in the `CTRL` control register. Clearing this bit
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resets the entire module including the RX and TX FIFOs.
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The SDI operates on byte-level only. Data written to the `DATA` register will be pushed to the TX FIFO. Received
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data can be retrieved by reading the RX FIFO via the `DATA` register. The current state of these FIFOs is available
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via the control register's `SDI_CTRL_RX_*` and `SDI_CTRL_TX_*` flags. The RX FIFO can be manually cleared at any time
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by setting the `SDI_CTRL_CLR_RX` bit.
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.MSB-first Only
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[NOTE]
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The NEORV32 SDI module only supports MSB-first mode.
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.Transmission Abort
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[NOTE]
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If the external SPI controller aborts an transmission (by setting the chip-select signal high again) _before_
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8 data bits have been transferred, no data is written to the RX FIFO.
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**SDI Clocking**
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The SDI module supports both SPI clock polarity modes ("CPOL") but regarding the clock phase only "CPHA=0" is supported
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yet. All SDI operations are clocked by the external `sdi_clk_i` signal. This signal is synchronized to the processor's
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clock domain to simplify timing behavior. However, the clock synchronization requires that the external SDI clock
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(`sdi_clk_i`) does **not exceed 1/4 of the processor's main clock**.
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**SDI Interrupt**
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The SDI module provides a set of programmable interrupt conditions based on the level of the RX & TX FIFOs. The different
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interrupt sources are enabled by setting the according control register's `SDI_CTRL_IRQ` bits. All enabled interrupt
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conditions are logically OR-ed so any enabled interrupt source will trigger the module's interrupt signal.
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Once the SDI interrupt has fired it will remain active until the actual cause of the interrupt is resolved; for
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example if just the `SDI_CTRL_IRQ_RX_AVAIL` bit is set, the interrupt will keep firing until the RX FIFO is empty again.
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Furthermore, an active SDI interrupt has to be explicitly cleared again by writing zero to the according
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<<_mip>> CSR bit.
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**Register Map**
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.SDI register map (`struct NEORV32_SDI`)
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[cols="<2,<1,<4,^1,<7"]
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[options="header",grid="all"]
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|=======================
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| Address | Name [C] | Bit(s), Name [C] | R/W | Function
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.16+<| `0xfffff700` .16+<| `CTRL` <|`0` `SDI_CTRL_EN` ^| r/w <| SDI module enable
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<|`1` `SDI_CTRL_CLR_RX` ^| -/w <| clear RX FIFO when set, bit auto-clears
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<|`3:2` _reserved_ ^| r/- <| reserved, read as zero
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<|`7:4` `SDI_CTRL_FIFO_MSB : SDI_CTRL_FIFO_LSB` ^| r/- <| FIFO depth; log2(_IO_SDI_FIFO_)
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<|`14:8` _reserved_ ^| r/- <| reserved, read as zero
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<|`15` `SDI_CTRL_IRQ_RX_AVAIL` ^| r/w <| fire interrupt if RX FIFO is not empty
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<|`16` `SDI_CTRL_IRQ_RX_HALF` ^| r/w <| fire interrupt if RX FIFO is at least half full
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<|`17` `SDI_CTRL_IRQ_RX_FULL` ^| r/w <| fire interrupt if if RX FIFO is full
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<|`18` `SDI_CTRL_IRQ_TX_EMPTY` ^| r/w <| fire interrupt if TX FIFO is empty
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<|`22:19` _reserved_ ^| r/- <| reserved, read as zero
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<|`23` `SDI_CTRL_RX_AVAIL` ^| r/- <| RX FIFO data available (RX FIFO not empty)
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<|`24` `SDI_CTRL_RX_HALF` ^| r/- <| RX FIFO at least half full
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<|`25` `SDI_CTRL_RX_FULL` ^| r/- <| RX FIFO full
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<|`26` `SDI_CTRL_TX_EMPTY` ^| r/- <| TX FIFO empty
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<|`27` `SDI_CTRL_TX_FULL` ^| r/- <| TX FIFO full
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<|`31:28` _reserved_ ^| r/- <| reserved, read as zero
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| `0xfffff704` | `DATA` |`7:0` | r/w | receive/transmit data (FIFO)
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|=======================
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