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--********************************************************************** -- Copyright 2012 by XESS Corp <http://www.xess.com>. -- This program is free software: you can redistribute it and/or modify -- it under the terms of the GNU General Public License as published by -- the Free Software Foundation, either version 3 of the License, or -- (at your option) any later version. -- -- This program is distributed in the hope that it will be useful, -- but WITHOUT ANY WARRANTY; without even the implied warranty of -- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the -- GNU General Public License for more details. -- -- You should have received a copy of the GNU General Public License -- along with this program. If not, see <http://www.gnu.org/licenses/>. --********************************************************************** --********************************************************************* -- SD MEMORY CARD INTERFACE -- -- Reads/writes a single or multiple blocks of data to/from an SD Flash card. -- -- Based on work by by Steven J. Merrifield, June 2008: -- http : //stevenmerrifield.com/tools/sd.vhd -- -- Most of what I learned about interfacing to SD/SDHC cards came from here: -- http://elm-chan.org/docs/mmc/mmc_e.html -- -- OPERATION -- -- Set-up: -- First of all, you have to give the controller a clock signal on the clk_i -- input with a higher frequency than the serial clock sent to the SD card -- through the sclk_o output. You can set generic parameters for the -- controller to tell it the master clock frequency (100 MHz), the SCLK -- frequency for initialization (400 KHz), the SCLK frequency for normal -- operation (25 MHz), the size of data sectors in the Flash memory (512 bytes), -- and the type of card (either SD or SDHC). I typically use a 100 MHz -- clock if I'm running an SD card with a 25 Mbps serial data stream. -- -- Initialize it: -- Pulsing the reset_i input high and then bringing it low again will make -- the controller initialize the SD card so it will work in SPI mode. -- Basically, it sends the card the commands CMD0, CMD8 and then ACMD41 (which -- is CMD55 followed by CMD41). The busy_o output will be high during the -- initialization and will go low once it is done. -- -- After the initialization command sequence, the SD card will send back an R1 -- response byte. If only the IDLE bit of the R1 response is set, then the -- controller will repeatedly re-try the ACMD41 command while busy_o remains -- high. -- -- If any other bit of the R1 response is set, then an error occurred. The -- controller will stall, lower busy_o, and output the R1 response code on the -- error_o bus. You'll have to pulse reset_i to unfreeze the controller. -- -- If the R1 response is all zeroes (i.e., no errors occurred during the -- initialization), then the controller will lower busy_o and wait for a -- read or write operation from the host. The controller will only accept new -- operations when busy_o is low. -- -- Write data: -- To write a data block to the SD card, the address of a block is placed -- on the addr_i input bus and the wr_i input is raised. The address and -- write strobe can be removed once busy_o goes high to indicate the write -- operation is underway. The data to be written to the SD card is passed as -- follows: -- -- 1. The controller requests a byte of data by raising the hndShk_o output. -- 2. The host applies the next byte to the data_i input bus and raises the -- hndShk_i input. -- 3. The controller accepts the byte and lowers the hndShk_o output. -- 4. The host lowers the hndShk_i input. -- -- This sequence of steps is repeated until all BLOCK_SIZE_G bytes of the -- data block are passed from the host to the controller. Once all the data -- is passed, the sector on the SD card will be written and the busy_o output -- will be lowered. -- -- Read data: -- To read a block of data from the SD card, the address of a block is -- placed on the addr_i input bus and the rd_i input is raised. The address -- and read strobe can be removed once busy_o goes high to indicate the read -- operation is underway. The data read from the SD card is passed to the -- host as follows: -- -- 1. The controller raises the hndShk_o output when the next data byte is available. -- 2. The host reads the byte from the data_o output bus and raises the hndShk_i input. -- 3. The controller lowers the hndShk_o output. -- 4. The host lowers the hndShk_i input. -- -- This sequence of steps is repeated until all BLOCK_SIZE_G bytes of the -- data block are passed from the controller to the host. Once all the data -- is read, the busy_o output will be lowered. -- -- Handle errors: -- If an error is detected during either a read or write operation, then the -- controller will stall, lower busy_o, and output an error code on the -- error_o bus. You'll have to pulse reset_i to unfreeze the controller. That -- may seem a bit excessive, but it does guarantee that you can't ignore any -- errors that occur. -- -- TODO: -- -- * Implement multi-block read and write commands. -- * Allow host to send/receive SPI commands/data directly to -- the SD card through the controller. -- ********************************************************************* library ieee; use ieee.std_logic_1164.all; use ieee.numeric_std.all; use work.CommonPckg.all; package SdCardPckg is type CardType_t is (SD_CARD_E, SDHC_CARD_E); -- Define the different types of SD cards. component SdCardCtrl is generic ( FREQ_G : real := 100.0; -- Master clock frequency (MHz). INIT_SPI_FREQ_G : real := 0.4; -- Slow SPI clock freq. during initialization (MHz). SPI_FREQ_G : real := 25.0; -- Operational SPI freq. to the SD card (MHz). BLOCK_SIZE_G : natural := 512; -- Number of bytes in an SD card block or sector. CARD_TYPE_G : CardType_t := SD_CARD_E -- Type of SD card connected to this controller. ); port ( -- Host-side interface signals. clk_i : in std_logic; -- Master clock. reset_i : in std_logic := '0'; -- active-high, synchronous reset. rd_i : in std_logic := '0'; -- active-high read block request. wr_i : in std_logic := '0'; -- active-high write block request. continue_i : in std_logic := '0'; -- If true, inc address and continue R/W. addr_i : in std_logic_vector(31 downto 0) := x"00000000"; -- Block address. data_i : in std_logic_vector(7 downto 0) := x"00"; -- Data to write to block. data_o : out std_logic_vector(7 downto 0) := x"00"; -- Data read from block. busy_o : out std_logic; -- High when controller is busy performing some operation. hndShk_i : in std_logic; -- High when host has data to give or has taken data. hndShk_o : out std_logic; -- High when controller has taken data or has data to give. error_o : out std_logic_vector(15 downto 0) := (others => '0'); -- I/O signals to the external SD card. cs_bo : out std_logic := '1'; -- Active-low chip-select. sclk_o : out std_logic := '0'; -- Serial clock to SD card. mosi_o : out std_logic := '1'; -- Serial data output to SD card. miso_i : in std_logic := '0' -- Serial data input from SD card. ); end component; end package; library ieee; use ieee.math_real.all; use ieee.std_logic_1164.all; use ieee.numeric_std.all; use work.CommonPckg.all; use work.SdCardPckg.all; entity SdCardCtrl is generic ( FREQ_G : real := 100.0; -- Master clock frequency (MHz). INIT_SPI_FREQ_G : real := 0.4; -- Slow SPI clock freq. during initialization (MHz). SPI_FREQ_G : real := 25.0; -- Operational SPI freq. to the SD card (MHz). BLOCK_SIZE_G : natural := 512; -- Number of bytes in an SD card block or sector. CARD_TYPE_G : CardType_t := SD_CARD_E -- Type of SD card connected to this controller. ); port ( -- Host-side interface signals. clk_i : in std_logic; -- Master clock. reset_i : in std_logic := '0'; -- active-high, synchronous reset. rd_i : in std_logic := '0'; -- active-high read block request. wr_i : in std_logic := '0'; -- active-high write block request. continue_i : in std_logic := '0'; -- If true, inc address and continue R/W. addr_i : in std_logic_vector(31 downto 0) := x"00000000"; -- Block address. data_i : in std_logic_vector(7 downto 0) := x"00"; -- Data to write to block. data_o : out std_logic_vector(7 downto 0) := x"00"; -- Data read from block. busy_o : out std_logic; -- High when controller is busy performing some operation. hndShk_i : in std_logic; -- High when host has data to give or has taken data. hndShk_o : out std_logic; -- High when controller has taken data or has data to give. error_o : out std_logic_vector(15 downto 0) := (others => '0'); -- I/O signals to the external SD card. cs_bo : out std_logic := '1'; -- Active-low chip-select. sclk_o : out std_logic := '0'; -- Serial clock to SD card. mosi_o : out std_logic := '1'; -- Serial data output to SD card. miso_i : in std_logic := '0'; -- Serial data input from SD card. state_debug_o : out std_logic_vector(4 downto 0) ); end entity; architecture arch of SdCardCtrl is signal sclk_r : std_logic := '0'; -- Register output drives SD card clock. signal hndShk_r : std_logic := '0'; -- Register output drives handshake output to host. signal state_debug : unsigned(4 downto 0); begin state_debug_o <= std_logic_vector(state_debug); process(clk_i) -- FSM process for the SD card controller. type FsmState_t is ( -- States of the SD card controller FSM. START_INIT, -- Send initialization clock pulses to the deselected SD card. SEND_CMD0, -- Put the SD card in the IDLE state. CHK_CMD0_RESPONSE, -- Check card's R1 response to the CMD0. SEND_CMD8, -- This command is needed to initialize SDHC cards. GET_CMD8_RESPONSE, -- Get the R7 response to CMD8. SEND_CMD55, -- Send CMD55 to the SD card. SEND_CMD41, -- Send CMD41 to the SD card. CHK_ACMD41_RESPONSE, -- Check if the SD card has left the IDLE state. WAIT_FOR_HOST_RW, -- Wait for the host to issue a read or write command. RD_BLK, -- Read a block of data from the SD card. WR_BLK, -- Write a block of data to the SD card. WR_WAIT, -- Wait for SD card to finish writing the data block. START_TX, -- Start sending command/data. TX_BITS, -- Shift out remaining command/data bits. GET_CMD_RESPONSE, -- Get the R1 response of the SD card to a command. RX_BITS, -- Receive response/data from the SD card. DESELECT, -- De-select the SD card and send some clock pulses (Must enter with sclk at zero.) PULSE_SCLK, -- Issue some clock pulses. (Must enter with sclk at zero.) REPORT_ERROR -- Report error and stall until reset. ); variable state_v : FsmState_t := START_INIT; -- Current state of the FSM. variable rtnState_v : FsmState_t; -- State FSM returns to when FSM subroutine completes. -- Timing constants based on the master clock frequency and the SPI SCLK frequencies. constant CLKS_PER_INIT_SCLK_C : real := FREQ_G / INIT_SPI_FREQ_G; constant CLKS_PER_SCLK_C : real := FREQ_G / SPI_FREQ_G; constant MAX_CLKS_PER_SCLK_C : real := realmax(CLKS_PER_INIT_SCLK_C, CLKS_PER_SCLK_C); constant MAX_CLKS_PER_SCLK_PHASE_C : natural := integer(round(MAX_CLKS_PER_SCLK_C / 2.0)); constant INIT_SCLK_PHASE_PERIOD_C : natural := integer(round(CLKS_PER_INIT_SCLK_C / 2.0)); constant SCLK_PHASE_PERIOD_C : natural := integer(round(CLKS_PER_SCLK_C / 2.0)); constant DELAY_BETWEEN_BLOCK_RW_C : natural := SCLK_PHASE_PERIOD_C; -- Registers for generating slow SPI SCLK from the faster master clock. variable clkDivider_v : natural range 0 to MAX_CLKS_PER_SCLK_PHASE_C; -- Holds the SCLK period. variable sclkPhaseTimer_v : natural range 0 to MAX_CLKS_PER_SCLK_PHASE_C; -- Counts down to zero, then SCLK toggles. constant NUM_INIT_CLKS_C : natural := 160; -- Number of initialization clocks to SD card. variable bitCnt_v : natural range 0 to NUM_INIT_CLKS_C; -- Tx/Rx bit counter. constant CRC_SZ_C : natural := 2; -- Number of CRC bytes for read/write blocks. -- When reading blocks of data, get 0xFE + [DATA_BLOCK] + [CRC]. constant RD_BLK_SZ_C : natural := 1 + BLOCK_SIZE_G + CRC_SZ_C; -- When writing blocks of data, send 0xFF + 0xFE + [DATA BLOCK] + [CRC] then receive response byte. constant WR_BLK_SZ_C : natural := 1 + 1 + BLOCK_SIZE_G + CRC_SZ_C + 1; variable byteCnt_v : natural range 0 to IntMax(WR_BLK_SZ_C, RD_BLK_SZ_C); -- Tx/Rx byte counter. -- Command bytes for various SD card operations. subtype Cmd_t is std_logic_vector(7 downto 0); constant CMD0_C : Cmd_t := std_logic_vector(to_unsigned(16#40# + 0, Cmd_t'length)); constant CMD8_C : Cmd_t := std_logic_vector(to_unsigned(16#40# + 8, Cmd_t'length)); constant CMD55_C : Cmd_t := std_logic_vector(to_unsigned(16#40# + 55, Cmd_t'length)); constant CMD41_C : Cmd_t := std_logic_vector(to_unsigned(16#40# + 41, Cmd_t'length)); constant READ_BLK_CMD_C : Cmd_t := std_logic_vector(to_unsigned(16#40# + 17, Cmd_t'length)); constant WRITE_BLK_CMD_C : Cmd_t := std_logic_vector(to_unsigned(16#40# + 24, Cmd_t'length)); -- Except for CMD0 and CMD8, SD card ops don't need a CRC, so use a fake one for that slot in the command. constant FAKE_CRC_C : std_logic_vector(7 downto 0) := x"FF"; variable addr_v : unsigned(addr_i'range); -- Address of current block for R/W operations. -- Maximum Tx to SD card consists of command + address + CRC. Data Tx is just a single byte. variable tx_v : std_logic_vector(CMD0_C'length + addr_v'length + FAKE_CRC_C'length - 1 downto 0); -- Data/command to SD card. alias txCmd_v is tx_v; -- Command transmission shift register. alias txData_v is tx_v(tx_v'high downto tx_v'high - data_i'length + 1); -- Data byte transmission shift register. variable rx_v : std_logic_vector(data_i'range); -- Data/response byte received from SD card. -- Various response codes. subtype Response_t is std_logic_vector(rx_v'range); constant ACTIVE_NO_ERRORS_C : Response_t := "00000000"; -- Normal R1 code after initialization. constant IDLE_NO_ERRORS_C : Response_t := "00000001"; -- Normal R1 code after CMD0. constant DATA_ACCEPTED_C : Response_t := "---00101"; -- SD card accepts data block from host. constant DATA_REJ_CRC_C : Response_t := "---01011"; -- SD card rejects data block from host due to CRC error. constant DATA_REJ_WERR_C : Response_t := "---01101"; -- SD card rejects data block from host due to write error. -- Various tokens. subtype Token_t is std_logic_vector(rx_v'range); constant NO_TOKEN_C : Token_t := x"FF"; -- Received before the SD card responds to a block read command. constant START_TOKEN_C : Token_t := x"FE"; -- Starting byte preceding a data block. -- Flags that are set/cleared to affect the operation of the FSM. variable getCmdResponse_v : boolean; -- When true, get R1 response to command sent to SD card. variable rtnData_v : boolean; -- When true, signal to host when a data byte arrives from SD card. variable doDeselect_v : boolean; -- When true, de-select SD card after a command is issued. begin if rising_edge(clk_i) then case( state_v ) is when START_INIT => state_debug <= to_unsigned(0, 5); when SEND_CMD0 => state_debug <= to_unsigned(1, 5); when CHK_CMD0_RESPONSE => state_debug <= to_unsigned(2, 5); when SEND_CMD8 => state_debug <= to_unsigned(3, 5); when GET_CMD8_RESPONSE => state_debug <= to_unsigned(4, 5); when SEND_CMD55 => state_debug <= to_unsigned(5, 5); when SEND_CMD41 => state_debug <= to_unsigned(6, 5); when CHK_ACMD41_RESPONSE => state_debug <= to_unsigned(7, 5); when WAIT_FOR_HOST_RW => state_debug <= to_unsigned(8, 5); when RD_BLK => state_debug <= to_unsigned(9, 5); when WR_BLK => state_debug <= to_unsigned(10, 5); when WR_WAIT => state_debug <= to_unsigned(11, 5); when START_TX => state_debug <= to_unsigned(12, 5); when TX_BITS => state_debug <= to_unsigned(13, 5); when GET_CMD_RESPONSE => state_debug <= to_unsigned(14, 5); when RX_BITS => state_debug <= to_unsigned(15, 5); when DESELECT => state_debug <= to_unsigned(16, 5); when PULSE_SCLK => state_debug <= to_unsigned(17, 5); when REPORT_ERROR => state_debug <= to_unsigned(18, 5); end case ; if reset_i = YES then -- Perform a reset. state_v := START_INIT; -- Send the FSM to the initialization entry-point. sclkPhaseTimer_v := 0; -- Don't delay the initialization right after reset. busy_o <= YES; -- Busy while the SD card interface is being initialized. elsif sclkPhaseTimer_v /= 0 then -- Setting the clock phase timer to a non-zero value delays any further actions -- and generates the slower SPI clock from the faster master clock. sclkPhaseTimer_v := sclkPhaseTimer_v - 1; -- Clock phase timer has reached zero, so check handshaking sync. between host and controller. -- Handshaking lets the host control the flow of data to/from the SD card controller. -- Handshaking between the SD card controller and the host proceeds as follows: -- 1: Controller raises its handshake and waits. -- 2: Host sees controller handshake and raises its handshake in acknowledgement. -- 3: Controller sees host handshake acknowledgement and lowers its handshake. -- 4: Host sees controller lower its handshake and removes its handshake. -- -- Handshaking is bypassed when the controller FSM is initializing the SD card. elsif state_v /= START_INIT and hndShk_r = '1' and hndShk_i = '0' then null; -- Waiting for the host to acknowledge handshake. elsif state_v /= START_INIT and hndShk_r = '1' and hndShk_i = '1' then txData_v := data_i; -- Get any data passed from the host. hndShk_r <= '0'; -- The host acknowledged, so lower the controller handshake. elsif state_v /= START_INIT and hndShk_r = '0' and hndShk_i = '1' then null; -- Waiting for the host to lower its handshake. elsif (state_v = START_INIT) or (hndShk_r = '0' and hndShk_i = '0') then -- Both handshakes are low, so the controller operations can proceed. busy_o <= YES; -- Busy by default. Only false when waiting for R/W from host or stalled by error. case state_v is when START_INIT => -- Deselect the SD card and send it a bunch of clock pulses with MOSI high. error_o <= (others => '0'); -- Clear error flags. clkDivider_v := INIT_SCLK_PHASE_PERIOD_C - 1; -- Use slow SPI clock freq during init. sclkPhaseTimer_v := INIT_SCLK_PHASE_PERIOD_C - 1; -- and set the duration of the next clock phase. sclk_r <= '0'; -- Start with low clock to the SD card. hndShk_r <= '0'; -- Initialize handshake signal. addr_v := (others => '0'); -- Initialize address. rtnData_v := false; -- No data is returned to host during initialization. bitCnt_v := NUM_INIT_CLKS_C; -- Generate this many clock pulses. state_v := DESELECT; -- De-select the SD card and pulse SCLK. rtnState_v := SEND_CMD0; -- Then go to this state after the clock pulses are done. when SEND_CMD0 => -- Put the SD card in the IDLE state. cs_bo <= '0'; -- Enable the SD card. txCmd_v := CMD0_C & x"00000000" & x"95"; -- 0x95 is the correct CRC for this command. bitCnt_v := txCmd_v'length; -- Set bit counter to the size of the command. getCmdResponse_v := true; -- Sending a command that generates a response. doDeselect_v := true; -- De-select SD card after this command finishes. state_v := START_TX; -- Go to FSM subroutine to send the command. rtnState_v := CHK_CMD0_RESPONSE; -- Then check the response to the command. when CHK_CMD0_RESPONSE => -- Check card's R1 response to the CMD0. if rx_v = IDLE_NO_ERRORS_C then state_v := SEND_CMD8; -- Continue init if SD card is in IDLE state with no errors else state_v := SEND_CMD0; -- Otherwise, try CMD0 again. end if; when SEND_CMD8 => -- This command is needed to initialize SDHC cards. cs_bo <= '0'; -- Enable the SD card. txCmd_v := CMD8_C & x"000001aa" & x"87"; -- 0x87 is the correct CRC for this command. bitCnt_v := txCmd_v'length; -- Set bit counter to the size of the command. getCmdResponse_v := true; -- Sending a command that generates a response. doDeselect_v := false; -- Don't de-select, need to get the R7 response sent from the SD card. state_v := START_TX; -- Go to FSM subroutine to send the command. rtnState_v := GET_CMD8_RESPONSE; -- Then go to this state after the command is sent. when GET_CMD8_RESPONSE => -- Get the R7 response to CMD8. cs_bo <= '0'; -- The SD card should already be enabled, but let's be explicit. bitCnt_v := 31; -- Four bytes (32 bits) in R7 response. getCmdResponse_v := false; -- Not sending a command that generates a response. doDeselect_v := true; -- De-select card to end the command after getting the four bytes. state_v := RX_BITS; -- Go to FSM subroutine to get the R7 response. rtnState_v := SEND_CMD55; -- Then go here (we don't care what the actual R7 response is). when SEND_CMD55 => -- Send CMD55 as preamble of ACMD41 initialization command. cs_bo <= '0'; -- Enable the SD card. txCmd_v := CMD55_C & x"00000000" & FAKE_CRC_C; bitCnt_v := txCmd_v'length; -- Set bit counter to the size of the command. getCmdResponse_v := true; -- Sending a command that generates a response. doDeselect_v := true; -- De-select SD card after this command finishes. state_v := START_TX; -- Go to FSM subroutine to send the command. rtnState_v := SEND_CMD41; -- Then go to this state after the command is sent. when SEND_CMD41 => -- Send the SD card the initialization command. cs_bo <= '0'; -- Enable the SD card. txCmd_v := CMD41_C & x"40000000" & FAKE_CRC_C; bitCnt_v := txCmd_v'length; -- Set bit counter to the size of the command. getCmdResponse_v := true; -- Sending a command that generates a response. doDeselect_v := true; -- De-select SD card after this command finishes. state_v := START_TX; -- Go to FSM subroutine to send the command. rtnState_v := CHK_ACMD41_RESPONSE; -- Then check the response to the command. when CHK_ACMD41_RESPONSE => -- The CMD55, CMD41 sequence should cause the SD card to leave the IDLE state -- and become ready for SPI read/write operations. If still IDLE, then repeat the CMD55, CMD41 sequence. -- If one of the R1 error flags is set, then report the error and stall. if rx_v = ACTIVE_NO_ERRORS_C then -- Not IDLE, no errors. state_v := WAIT_FOR_HOST_RW; -- Start processing R/W commands from the host. elsif rx_v = IDLE_NO_ERRORS_C then -- Still IDLE but no errors. state_v := SEND_CMD55; -- Repeat the CMD55, CMD41 sequence. else -- Some error occurred. state_v := REPORT_ERROR; -- Report the error and stall. end if; when WAIT_FOR_HOST_RW => -- Wait for the host to read or write a block of data from the SD card. clkDivider_v := SCLK_PHASE_PERIOD_C - 1; -- Set SPI clock frequency for normal operation. getCmdResponse_v := true; -- Get R1 response to any commands issued to the SD card. if rd_i = YES then -- send READ command and address to the SD card. cs_bo <= '0'; -- Enable the SD card. if continue_i = YES then -- Multi-block read. Use stored address. if CARD_TYPE_G = SD_CARD_E then -- SD cards use byte-addressing, addr_v := addr_v + BLOCK_SIZE_G; -- so add block-size to get next block address. else -- SDHC cards use block-addressing, addr_v := addr_v + 1; -- so just increment current block address. end if; txCmd_v := READ_BLK_CMD_C & std_logic_vector(addr_v) & FAKE_CRC_C; else -- Single-block read. txCmd_v := READ_BLK_CMD_C & addr_i & FAKE_CRC_C; -- Use address supplied by host. addr_v := unsigned(addr_i); -- Store address for multi-block operations. end if; bitCnt_v := txCmd_v'length; -- Set bit counter to the size of the command. byteCnt_v := RD_BLK_SZ_C; state_v := START_TX; -- Go to FSM subroutine to send the command. rtnState_v := RD_BLK; -- Then go to this state to read the data block. elsif wr_i = YES then -- send WRITE command and address to the SD card. cs_bo <= '0'; -- Enable the SD card. if continue_i = YES then -- Multi-block write. Use stored address. if CARD_TYPE_G = SD_CARD_E then -- SD cards use byte-addressing, addr_v := addr_v + BLOCK_SIZE_G; -- so add block-size to get next block address. else -- SDHC cards use block-addressing, addr_v := addr_v + 1; -- so just increment current block address. end if; txCmd_v := WRITE_BLK_CMD_C & std_logic_vector(addr_v) & FAKE_CRC_C; else -- Single-block write. txCmd_v := WRITE_BLK_CMD_C & addr_i & FAKE_CRC_C; -- Use address supplied by host. addr_v := unsigned(addr_i); -- Store address for multi-block operations. end if; bitCnt_v := txCmd_v'length; -- Set bit counter to the size of the command. byteCnt_v := WR_BLK_SZ_C; -- Set number of bytes to write. state_v := START_TX; -- Go to this FSM subroutine to send the command ... rtnState_v := WR_BLK; -- then go to this state to write the data block. else -- Do nothing and wait for command from host. cs_bo <= '1'; -- Deselect the SD card. busy_o <= '0'; -- SD card interface is waiting for R/W from host, so it's not busy. state_v := WAIT_FOR_HOST_RW; -- Keep waiting for command from host. end if; when RD_BLK => -- Read a block of data from the SD card. -- Some default values for these... rtnData_v := false; -- Data is only returned to host in one place. bitCnt_v := rx_v'length - 1; -- Receiving byte-sized data. state_v := RX_BITS; -- Call the bit receiver routine. rtnState_v := RD_BLK; -- Return here when done receiving a byte. if byteCnt_v = RD_BLK_SZ_C then -- Initial read to prime the pump. byteCnt_v := byteCnt_v - 1; elsif byteCnt_v = RD_BLK_SZ_C -1 then -- Then look for the data block start token. if rx_v = NO_TOKEN_C then -- Receiving 0xFF means the card hasn't responded yet. Keep trying. null; elsif rx_v = START_TOKEN_C then rtnData_v := true; -- Found the start token, so now start returning data byes to the host. byteCnt_v := byteCnt_v - 1; else -- Getting anything else means something strange has happened. state_v := REPORT_ERROR; end if; elsif byteCnt_v >= 3 then -- Now bytes of data from the SD card are received. rtnData_v := true; -- Return this data to the host. byteCnt_v := byteCnt_v - 1; elsif byteCnt_v = 2 then -- Receive the 1st CRC byte at the end of the data block. byteCnt_v := byteCnt_v - 1; elsif byteCnt_v = 1 then -- Receive the 2nd byteCnt_v := byteCnt_v - 1; else -- Reading is done, so deselect the SD card. sclk_r <= '0'; bitCnt_v := 2; state_v := DESELECT; rtnState_v := WAIT_FOR_HOST_RW; end if; when WR_BLK => -- Write a block of data to the SD card. -- Some default values for these... getCmdResponse_v := false; -- Sending data bytes so there's no command response from SD card. bitCnt_v := txData_v'length; -- Transmitting byte-sized data. state_v := START_TX; -- Call the bit transmitter routine. rtnState_v := WR_BLK; -- Return here when done transmitting a byte. if byteCnt_v = WR_BLK_SZ_C then txData_v := NO_TOKEN_C; -- Hold MOSI high for one byte before data block goes out. elsif byteCnt_v = WR_BLK_SZ_C - 1 then -- Send start token. txData_v := START_TOKEN_C; -- Starting token for data block. elsif byteCnt_v >= 4 then -- Now send bytes in the data block. hndShk_r <= '1'; -- Signal host to provide data. -- The transmit shift register is loaded with data from host in the handshaking section above. elsif byteCnt_v = 3 or byteCnt_v = 2 then -- Send two phony CRC bytes at end of packet. txData_v := FAKE_CRC_C; elsif byteCnt_v = 1 then bitCnt_v := rx_v'length - 1; state_v := RX_BITS; -- Get response of SD card to the write operation. rtnState_v := WR_WAIT; else -- Check received response byte. if std_match(rx_v, DATA_ACCEPTED_C) then -- Data block was accepted. state_v := WR_WAIT; -- Wait for the SD card to finish writing the data into Flash. else -- Data block was rejected. error_o(15 downto 8) <= rx_v; state_v := REPORT_ERROR; -- Report the error. end if; end if; byteCnt_v := byteCnt_v - 1; when WR_WAIT => -- Wait for SD card to finish writing the data block. -- The SD card will pull MISO low while it is busy, and raise it when it is done. sclk_r <= not sclk_r; -- Toggle the SPI clock... sclkPhaseTimer_v := clkDivider_v; -- and set the duration of the next clock phase. if sclk_r = '1' and miso_i = '1' then -- Data block has been written, so deselect the SD card. bitCnt_v := 2; state_v := DESELECT; rtnState_v := WAIT_FOR_HOST_RW; end if; when START_TX => -- Start sending command/data by lowering SCLK and outputing MSB of command/data -- so it has plenty of setup before the rising edge of SCLK. sclk_r <= '0'; -- Lower the SCLK (although it should already be low). sclkPhaseTimer_v := clkDivider_v; -- Set the duration of the low SCLK. mosi_o <= tx_v(tx_v'high); -- Output MSB of command/data. tx_v := tx_v(tx_v'high-1 downto 0) & ONE; -- Shift command/data register by one bit. bitCnt_v := bitCnt_v - 1; -- The first bit has been sent, so decrement bit counter. state_v := TX_BITS; -- Go here to shift out the rest of the command/data bits. when TX_BITS => -- Shift out remaining command/data bits and (possibly) get response from SD card. sclk_r <= not sclk_r; -- Toggle the SPI clock... sclkPhaseTimer_v := clkDivider_v; -- and set the duration of the next clock phase. if sclk_r = '1' then -- SCLK is going to be flipped from high to low, so output the next command/data bit -- so it can setup while SCLK is low. if bitCnt_v /= 0 then -- Keep sending bits until the bit counter hits zero. mosi_o <= tx_v(tx_v'high); tx_v := tx_v(tx_v'high-1 downto 0) & ONE; bitCnt_v := bitCnt_v - 1; else if getCmdResponse_v then state_v := GET_CMD_RESPONSE; -- Get a response to the command from the SD card. bitCnt_v := Response_t'length - 1; -- Length of the expected response. else state_v := rtnState_v; -- Return to calling state (no need to get a response). sclkPhaseTimer_v := 0; -- Clear timer so next SPI op can begin ASAP with SCLK low. end if; end if; end if; when GET_CMD_RESPONSE => -- Get the response of the SD card to a command. if sclk_r = '1' and miso_i = '0' then -- MISO will be held high by SD card until 1st bit of R1 response, which is 0. -- Shift in the MSB bit of the response. rx_v := rx_v(rx_v'high-1 downto 0) & miso_i; bitCnt_v := bitCnt_v - 1; state_v := RX_BITS; -- Now receive the reset of the response. end if; sclk_r <= not sclk_r; -- Toggle the SPI clock... sclkPhaseTimer_v := clkDivider_v; -- and set the duration of the next clock phase. when RX_BITS => -- Receive bits from the SD card. if sclk_r = '1' then -- Bits enter after the rising edge of SCLK. rx_v := rx_v(rx_v'high-1 downto 0) & miso_i; if bitCnt_v /= 0 then -- More bits left to receive. bitCnt_v := bitCnt_v - 1; else -- Last bit has been received. if rtnData_v then -- Send the received data to the host. data_o <= rx_v; -- Output received data to the host. hndShk_r <= '1'; -- Signal to the host that the data is ready. end if; if doDeselect_v then bitCnt_v := 1; state_v := DESELECT; -- De-select SD card before returning. else state_v := rtnState_v; -- Otherwise, return to calling state without de-selecting. end if; end if; end if; sclk_r <= not sclk_r; -- Toggle the SPI clock... sclkPhaseTimer_v := clkDivider_v; -- and set the duration of the next clock phase. when DESELECT => -- De-select the SD card and send some clock pulses (Must enter with sclk at zero.) doDeselect_v := false; -- Once the de-select is done, clear the flag that caused it. cs_bo <= '1'; -- De-select the SD card. mosi_o <= '1'; -- Keep the data input of the SD card pulled high. state_v := PULSE_SCLK; -- Pulse the clock so the SD card will see the de-select. sclk_r <= '0'; -- Clock is set low so the next rising edge will see the new CS and MOSI sclkPhaseTimer_v := clkDivider_v; -- Set the duration of the next clock phase. when PULSE_SCLK => -- Issue some clock pulses. (Must enter with sclk at zero.) if sclk_r = '1' then if bitCnt_v /= 0 then bitCnt_v := bitCnt_v - 1; else -- Return to the calling routine when the pulse counter reaches zero. state_v := rtnState_v; end if; end if; sclk_r <= not sclk_r; -- Toggle the SPI clock... sclkPhaseTimer_v := clkDivider_v; -- and set the duration of the next clock phase. when REPORT_ERROR => -- Report the error code and stall here until a reset occurs. error_o(rx_v'range) <= rx_v; -- Output the SD card response as the error code. busy_o <= '0'; -- Not busy. when others => state_v := START_INIT; end case; end if; end if; end process; sclk_o <= sclk_r; -- Output the generated SPI clock for the SD card. hndShk_o <= hndShk_r; -- Output the generated handshake to the host. end architecture;