firmware: Import of the boot code

This is what gets embedded in the bitstream and loads the
main software from flash.

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>

firmware/boot/Makefile

@@ -0,0 +1,24 @@
+CROSS ?= riscv-none-embed-
+
+CC := $(CROSS)gcc
+OBJCOPY := $(CROSS)objcopy
+
+CFLAGS=-Wall -Os -march=rv32i -mabi=ilp32 -ffreestanding -flto -nostartfiles -fomit-frame-pointer -Wl,--gc-section --specs=nano.specs
+
+
+all: boot.hex
+
+
+boot.elf: lnk-boot.lds boot.S
+	$(CC) $(CFLAGS) -Wl,-Bstatic,-T,lnk-boot.lds,--strip-debug -DAPP_FLASH_ADDR=0x000a0000 -o $@ boot.S
+
+%.bin: %.elf
+	$(OBJCOPY) -O binary $< $@
+
+%.hex: %.bin
+	hexdump boot.bin -ve '1/4 "%08x\n"' $< > $@
+
+clean:
+	rm -f *.bin *.hex *.elf *.o
+
+.PHONY: clean

firmware/boot/boot.S

@@ -0,0 +1,193 @@
+/*
+ * boot.S
+ *
+ * SPI boot code
+ *
+ * Copyright (C) 2020-2023 Sylvain Munaut <tnt@246tNt.com>
+ * SPDX-License-Identifier: MIT
+ */
+
+#ifndef APP_FLASH_ADDR
+#define APP_FLASH_ADDR 0x000a0000
+#endif
+
+#ifndef APP_SRAM_ADDR
+#define APP_SRAM_ADDR 0x00020000
+#endif
+
+#ifndef APP_SIZE
+#define APP_SIZE 0x00010000
+#endif
+
+	.section .text.start
+	.global _start
+_start:
+
+	// SPI init
+	jal	spi_init
+	jal	spi_wakeup
+
+	// Read from flash to SRAM
+	li	a0, APP_SRAM_ADDR
+	li	a1, APP_SIZE
+	li	a2, APP_FLASH_ADDR
+	jal	spi_flash_read
+
+	// Setup reboot code
+	li	t0, 0x0002006f
+	sw	t0, 0(zero)
+
+	// Jump to main code
+	j	APP_SRAM_ADDR
+
+
+// ---------------------------------------------------------------------------
+// SB_SPI driver code
+// ---------------------------------------------------------------------------
+
+// Register definitions
+
+	.equ	SPI_BASE, 0x81000000
+
+	.equ	SPICR0,  4 * 0x08
+	.equ	SPICR1,  4 * 0x09
+	.equ	SPICR2,  4 * 0x0a
+	.equ	SPIBR,   4 * 0x0b
+	.equ	SPISR,   4 * 0x0c
+	.equ	SPITXDR, 4 * 0x0d
+	.equ	SPIRXDR, 4 * 0x0e
+	.equ	SPICSR,  4 * 0x0f
+
+
+// Initializes te SPI hardware
+//
+// Clobbers a0, a1
+
+spi_init:
+	li	a0, SPI_BASE
+
+	li	a1, 0xff
+	sw	a1, SPICR0(a0)
+
+	li	a1, 0x80
+	sw	a1, SPICR1(a0)
+
+	li	a1, 0xc0
+	sw	a1, SPICR2(a0)
+
+	li	a1, 0x03
+	sw	a1, SPIBR(a0)
+
+	li	a1, 0x0f
+	sw	a1, SPICSR(a0)
+
+	ret
+
+
+//
+// Wake up flash
+//
+spi_wakeup:
+
+	mv	s2, ra
+
+	// Setup CS
+	li	t0, SPI_BASE
+	li	t1, 0x0e
+	sw	t1, SPICSR(t0)
+
+	// Send command
+	li	a0, 0xAB
+	jal	_spi_do_one
+
+	// Release CS
+	li	t0, SPI_BASE
+	li	t1, 0x0f
+	sw	t1, SPICSR(t0)
+
+	// Wait a bit
+	li	s1, 0x10000
+1:
+	addi	s1, s1, -1
+	bne	s1, zero, 1b
+
+	// Done
+	jr	s2
+
+
+// Reads a block of memory from SPI flash
+//
+// Params:
+//  a0 - destination pointer
+//  a1 - length (bytes)
+//  a2 - flash offset
+// Clobbers t0, t1, s0, s1, s2
+
+spi_flash_read:
+	// Save params
+	mv	s0, a0
+	mv	s1, a1
+	mv	s2, ra
+
+	// Setup CS
+	li	t0, SPI_BASE
+	li	t1, 0x0e
+	sw	t1, SPICSR(t0)
+
+	// Send command
+	li	a0, 0x03
+	jal	_spi_do_one
+
+	srli	a0, a2, 16
+	and	a0, a0, 0xff
+	jal	_spi_do_one
+
+	srli	a0, a2, 8
+	and	a0, a0, 0xff
+	jal	_spi_do_one
+
+	and	a0, a2, 0xff
+	jal	_spi_do_one
+
+	// Read loop
+_spi_loop:
+	li	a0, 0x00
+	jal	_spi_do_one
+	sb	a0, 0(s0)
+	addi	s0, s0,  1
+	addi	s1, s1, -1
+	bne	s1, zero, _spi_loop
+
+	// Release CS
+	li	t0, SPI_BASE
+	li	t1, 0x0f
+	sw	t1, SPICSR(t0)
+
+	// Done
+	jr	s2
+
+
+// Performs a single 8 bit SPI xfer
+//
+// Params:  a0 - Data to TX
+// Returns: a0 - RX data
+// Clobbers t0, t1
+
+_spi_do_one:
+	li	t0, SPI_BASE
+	li	t1, 0x08
+
+	// Write TX data
+	sw	a0, SPITXDR(t0)
+
+	// Wait for RXRDY
+1:
+	lw	a0, SPISR(t0)
+	and	a0, a0, t1
+	bne	a0, t1, 1b
+
+	// Read RX data
+	lw	a0, SPIRXDR(t0)
+
+	// Done
+	ret

firmware/boot/lnk-boot.lds

@@ -0,0 +1,14 @@
+MEMORY
+{
+    ROM (rx)    : ORIGIN = 0x00000000, LENGTH = 0x0400
+}
+ENTRY(_start)
+SECTIONS {
+    .text :
+    {
+        . = ALIGN(4);
+        *(.text.start)
+        *(.text)
+        *(.text*)
+    } >ROM
+}