Rewrite rp2040 boot2 in Ada. Currently broken, need a CRC32 at the end

of the .boot2 section for the boot ROM to verify. I don't know how to do
that.

Author: JeremyGrosser

arm/cortexm.py

@@ -1107,6 +1107,7 @@ def __init__(self, smp):
             'arm/rpi/rp2040/svd/i-rp2040-sio.ads',
             'arm/rpi/rp2040/svd/i-rp2040-timer.ads',
             'arm/rpi/rp2040/svd/i-rp2040-watchdog.ads',
+            'arm/rpi/rp2040/svd/i-rp2040-xip_ssi.ads',
             'arm/rpi/rp2040/svd/i-rp2040-xosc.ads',
             'arm/rpi/rp2040/s-bbmcpa.ads.tmpl',
             'arm/rpi/rp2040/start-rom.S.tmpl',
@@ -1187,7 +1188,8 @@ def __init__(self, smp):
                                loader='RAM')
 
         self.add_gnat_sources(
-            'arm/rpi/rp2040/boot2__w25q080.S',)
+            'arm/rpi/rp2040/boot2.adb',
+            'arm/rpi/rp2040/boot2_generic_03.ads')
 
 
 class CortexM1(ArmV6MTarget):

arm/rpi/rp2040/boot2.adb

@@ -0,0 +1,28 @@
+--  The SSI cannot be configured while enabled, so the boot ROM copies the
+--  first 256 bytes of flash (referred to by the linker as .boot2) to SRAM and
+--  executes it. This procedure should disable SSI, configure it for the flash
+--  chip in use, re-enable SSI, then jump to the reset vector in XIP memory.
+--
+--  This is the generic version for all SPI flash chips that respond to the
+--  0x03 read command.
+with Interfaces.RP2040.XIP_SSI; use Interfaces.RP2040.XIP_SSI;
+with Boot2_Generic_03;          use Boot2_Generic_03;
+
+procedure Boot2
+   with Linker_Section => ".boot2"
+is
+begin
+   --  Disable SSI
+   XIP_SSI_Periph.SSIENR.SSI_EN := False;
+
+   --  Configure SSI
+   XIP_SSI_Periph.BAUDR := BAUDR;
+   XIP_SSI_Periph.CTRLR0 := CTRLR0;
+   XIP_SSI_Periph.SPI_CTRLR0 := SPI_CTRLR0;
+
+   --  Single 32b read XXX why is this here????
+   XIP_SSI_Periph.CTRLR1.NDF := 0;
+
+   --  Enable SSI
+   XIP_SSI_Periph.SSIENR.SSI_EN := True;
+end Boot2;

arm/rpi/rp2040/boot2_generic_03.ads

@@ -0,0 +1,22 @@
+with Interfaces.RP2040.XIP_SSI; use Interfaces.RP2040.XIP_SSI;
+
+package Boot2_Generic_03 is
+   --  Clock divider for flash, must be even (clk_sys / SCKDV)
+   BAUDR      : constant BAUDR_Register :=
+      (SCKDV  => 4,
+       others => <>);
+
+   CTRLR0     : constant CTRLR0_Register :=
+      (DFS_32  => 31,            --  Data frame size (minus 1)
+       SPI_FRF => STD,           --  Frame format
+       TMOD    => EEPROM_READ,   --  Transfer mode
+       others  => <>);
+
+   SPI_CTRLR0 : constant SPI_CTRLR0_Register :=
+      (TRANS_TYPE  => Val_1C1A, --  Command and address frame format
+       ADDR_L      => 6,        --  Address bits divided by 4
+       INST_L      => Val_8B,   --  Instruction length
+       WAIT_CYCLES => 0,        --  Clocks after mode bits
+       XIP_CMD     => 16#03#,   --  SPI read command
+       others      => <>);
+end Boot2_Generic_03;

arm/rpi/rp2040/start-rom.S.tmpl

@@ -171,4 +171,4 @@ __gnat_sys_tick_trap:
 fault:	b fault
 
 /* Hack to force the linker to link boot2.o */
-.word __boot2
+.word _ada_boot2