gateware/common/fw/boot.S

/*
 * boot.S
 *
 * SPI boot code
 *
 * Copyright (C) 2020-2022 Sylvain Munaut <tnt@246tNt.com>
 * SPDX-License-Identifier: MIT
 */

// #define BOOT_DEBUG
// (also set UART_DIV for the board below !)

#ifndef APP_FLASH_ADDR
#define APP_FLASH_ADDR 0x00100000
#endif

#ifndef APP_SRAM_ADDR
#define APP_SRAM_ADDR 0x00020000
#endif

#ifndef APP_SIZE
#define APP_SIZE 0x00010000
#endif

	.equ	UART_BASE, 0x81000000
	.equ	UART_DIV, 29	// 30.72 MHz / (29+2) ~= 1 Mbaud (icE1usb)
	//.equ	UART_DIV, 22	// 24    MHz / (22+2) ~= 1 Mbaud (e1-tracer)

	.section .text.start
	.global _start
_start:
	// Debug
#ifdef BOOT_DEBUG
	// Set UART divisor
	li	a0, UART_BASE
	li	a1, UART_DIV
	sw	a1, 4(a0)

	// Output 'a'
	li	a1, 97
	sw	a1, 0(a0)
#endif

	// SPI init
	jal	spi_init

	// Debug
#ifdef BOOT_DEBUG
	// Output 'b'
	li	a0, UART_BASE
	li	a1, 98
	sw	a1, 0(a0)
#endif

	// Read from flash to SRAM
	li	a0, APP_SRAM_ADDR
	li	a1, APP_SIZE
	li	a2, APP_FLASH_ADDR
	jal	spi_flash_read

	// Debug
#ifdef BOOT_DEBUG
	// Output 'c'
	li	a0, UART_BASE
	li	a1, 99
	sw	a1, 0(a0)
#endif

	// 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, 0x80000000

	.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


// 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