spi.s

# This test code is to demonstrate SPI functionality of the
# Pipelined RV32IMC + Protocol controllers
# NOTE: The SPI Controller for this project can only send
# 2 bytes per transaction. Interrupts are also triggered at the end of every transaction.
# =========================================================
# Demo setup:
# ESP8266 <---> CORE <---> Arduino Uno
# ESP8266: Slave 2
# Arduino: Slave 3
# Program flow:
# 1. CORE sends 2 byte packages to both slaves in ASCII (ES (ESP), AU (Arduino)).
# 2. If both slaves receive the correct package, they send a reply: (0xAA). 
#  	 If reply matches expected data, send command to both slaves to turn on their built-in LEDs (EL, AL)
# 	 Else, send "XX"
# =========================================================
# Register usage:
#		s0 -> SPI BUSY
#		s1 -> SPI DONE
#		s2 -> SPI Data Out
#		sp -> Stack pointer; points to word address 0x3FF
#		gp -> points to PROTOCOLMEM address (0x400)
#		a0-a1 -> return values
# 		a2-a7 -> subroutine arguments

.text
init:
	addi sp, x0, 0x3FF			# stack pointer addr
	c.slli sp, 2
	addi gp, x0, 0x400			# PROTOCOLMEM addr
	c.slli gp, 2

spi_setup:
	# Settings: 100kbps, cpha = 0, cpol = 0 (shift@negedge, sample@posedge), ord = 0 (send MSB first)
	addi t0, x0, 124			# 100kbps prescale
	c.slli t0, 8				# shift to prescale field
	# c.addi t0, 0xc				# ord = 0, cpha=1, cpol=1
	sw t0, 0x8(x0)				# store to SPI Input Control

main:
	# First part: CORE sends 2 byte packages to ESP8266 & Arduino
	# Send to ESP first
	lui a2, 0x04553				# send "ES"
	c.srli a2, 12				# shift s.t. LSB is at bit0
	c.li a3, 2					# select slave 2
	c.jal spi_write				# call spi_write(a2, a3)

	# Send to Arduino
	lui a2, 0x04155				# send "AU"
	c.srli a2, 12				# shift s.t. LSB is at bit0
	c.li a3, 3					# select slave 3
	c.jal spi_write				# call spi_write(a2, a3)

	# Second part: read reply from ESP8266 & Arduino & send command to turn on builtin LED
	# Get ESP reply
	c.li a2, 2					# select slave 2
	c.jal spi_read				# call spi_read
	addi t0, x0, 0xAA			# "0xAA"

	lui a2, 0x0454C				# "EL"
	beq a0, t0, main1			# check if data matches expected. If yes, skip "XX"
	lui a2, 0x05858				# "XX"
	main1:
	c.srli a2, 12				# shift s.t. LSB at bit0
	c.li a3, 2					# select slave 2
	c.jal spi_write				# call spi_write(a2, a3)

	# Get Arduino reply
	c.li a2, 3					# select slave 3
	c.jal spi_read				# call spi_read(a2)
	addi t0, x0, 0xAA			# 0xAA