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spi: Send dummy clocks at boot

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When using an FPGA which routes the SPI clock via STARTUPE2 as is
done on the Nexys Video (or optionally on Arty), the HW needs at
least 3 beats of that clock to complete the switch from the internal
config clock to the one we provide.

This works around it by having the SPI controller send 8 dummy
clocks at boot time with CS held high.

Without this, flash identification will fail those boards

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This commit is contained in:
Benjamin Herrenschmidt
2020-07-08 16:13:27 +10:00
parent bf36ea365b
commit 3c2739e10a
1 changed files with 19 additions and 7 deletions
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26
spi_flash_ctrl.vhdl
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@@ -11,6 +11,9 @@ entity spi_flash_ctrl is
DEF_CLK_DIV : natural := 2; -- Clock divider SCK = CLK/((CLK_DIV+1)*2)
DEF_QUAD_READ : boolean := false; -- Use quad read with 8 clk dummy
-- Dummy clocks after boot
BOOT_CLOCKS : boolean := true; -- Send 8 dummy clocks after boot
-- Number of data lines (1=MISO/MOSI, otherwise 2 or 4)
DATA_LINES : positive := 1
);
@@ -103,7 +106,7 @@ architecture rtl of spi_flash_ctrl is
constant DEFAULT_CS_TIMEOUT : integer := 32;
-- Automatic mode state
type auto_state_t is (AUTO_IDLE, AUTO_CS_ON, AUTO_CMD,
type auto_state_t is (AUTO_BOOT, AUTO_IDLE, AUTO_CS_ON, AUTO_CMD,
AUTO_ADR0, AUTO_ADR1, AUTO_ADR2, AUTO_ADR3,
AUTO_DUMMY,
AUTO_DAT0, AUTO_DAT1, AUTO_DAT2, AUTO_DAT3,
@@ -125,7 +128,7 @@ architecture rtl of spi_flash_ctrl is
-- Automatic mode latches
signal auto_data : std_ulogic_vector(wb_out.dat'left downto 0) := (others => '0');
signal auto_cnt : integer range 0 to 63 := 0;
signal auto_state : auto_state_t := AUTO_IDLE;
signal auto_state : auto_state_t := AUTO_BOOT;
signal auto_last_addr : std_ulogic_vector(31 downto 0);
begin
@@ -176,7 +179,7 @@ begin
-- in practice.
--
if cmd_valid = '1' and cmd_ready = '1' then
pending_read <= '1';
pending_read <= not wb_req.we;
elsif bus_idle = '1' then
pending_read <= '0';
end if;
@@ -396,21 +399,29 @@ begin
if rst = '1' or ctrl_reset = '1' then
auto_cs <= '0';
auto_cnt_next <= 0;
auto_next <= AUTO_IDLE;
auto_next <= AUTO_BOOT;
else
-- Run counter
if auto_cnt /= 0 then
auto_cnt_next <= auto_cnt - 1;
end if;
-- Automatic CS is set whenever state isn't IDLE or RECOVERY
if auto_state /= AUTO_IDLE and
auto_state /= AUTO_RECOVERY then
-- Automatic CS is set whenever state isn't IDLE or RECOVERY or BOOT
if auto_state /= AUTO_IDLE and
auto_state /= AUTO_RECOVERY and
auto_state /= AUTO_BOOT then
auto_cs <= '1';
end if;
-- State machine
case auto_state is
when AUTO_BOOT =>
if BOOT_CLOCKS then
auto_cmd_valid <= '1';
if cmd_ready = '1' then
auto_next <= AUTO_IDLE;
end if;
end if;
when AUTO_IDLE =>
-- Access to the memory map only when manual CS isn't set
if wb_map_valid = '1' and ctrl_cs = '0' then
@@ -599,3 +610,4 @@ begin
end process;
end architecture;