Group DebugStub

# mComPortAddresses = 0x3F8, 0x2F8, 0x3E8, 0x2E8;
# Currently hardcoded to COM1.
var ComAddr = $03F8

# All information relating to our serial usage should be documented in this comment.
# http://wiki.osdev.org/Serial_ports
#
# We do not use IRQs for debugstub serial. This is becuase DebugStub (DS)
# MUST be:
#  - As simple as possible
#  - Interact as minimal as possible wtih normal Cosmos code because
#    the debugstub must *always* work even if the normal code is fubarred
#
# The serial port that is used for DS should be 'hidden' from Cosmos main
# so that Cosmos main pretends it does not exist.
#
# IRQs would create a clash/mix of code.
# This does make the serial code in DebugStub inefficient, but its well worth
# the benefits received by following these rules.
#
# Baud rate is set to 115200. Likely our code could not exceed this rate
# anyways the way it is written and there are compatibility issues on some
# hardware above this rate.
#
# We assume a minimum level of a 16550A, which should be no problem on any 
# common hardware today. VMWare emulates the 16550A
#
# We do not handle flow control for outbound data (DS --> DC).
# The DebugConnector (DC, the code in the Visual Studio side) however is threaded
# and easily should be able to receive data faster than we can send it.
# Most things are transactional with data being sent only when asked for, but 
# with tracing we do send a data directly.
#
# Currently there is no inbound flow control either (DC --> DS)
# For now we assume all commands in bound are 16 bytes or less to ensure
# that they fit in the FIFO. Commands in DS must wait for a command ID ACK
# before sending another command.
# See notes in ProcessCommand.
#
# http:#www.nondot.org/sabre/os/files/Communication/ser_port.txt

# Todo Auto params
# Todo ebp frame ptr auto etc
procedure InitSerial {
	DX = .ComAddr

	# Disable interrupts
	BX = DX
	DX + 1
	AL = 0
	Port[DX] = AL

	# Enable DLAB (set baud rate divisor)
	DX = BX
	DX + 3
	AL = $80
	Port[DX] = AL

	# 0x01, 0x00 - 115200
	# 0x02, 0x00 - 57600
	# 0x03, 0x00 - 38400
	#
	# Set divisor (lo byte)
	DX = BX
	AL = $01
	Port[DX] = AL
	# hi byte
	DX = BX
	DX + 1
	AL = $00
	Port[DX] = AL

	# 8N1
	DX = BX
	DX + 3
	AL = $03
	Port[DX] = AL

	# Enable FIFO, clear them
	# Set 14-byte threshold for IRQ.
	# We dont use IRQ, but you cant set it to 0
	# either. IRQ is enabled/diabled separately
	DX = BX
	DX + 2
	AL = $C7
	Port[DX] = AL

	# 0x20 AFE Automatic Flow control Enable - 16550 (VMWare uses 16550A) is most common and does not support it
	# 0x02 RTS
	# 0x01 DTR
	# Send 0x03 if no AFE
	DX = BX
	DX + 4
	AL = $03
	Port[DX] = AL
}

# Modifies: AL, DX
procedure ComReadAL {
	DX = .ComAddr
	DX + 5
Wait:
    AL = Port[DX]
    AL ?& $01
    if 0 goto Wait

	DX = .ComAddr
    AL = Port[DX]
}
procedure ComReadEAX {
	Call .ComReadAL
	EAX ~> 8
	Call .ComReadAL
	EAX ~> 8
	Call .ComReadAL
	EAX ~> 8
	Call .ComReadAL
	EAX ~> 8
}

# Input: EDI
# Output: [EDI]
# Modified: AL, DX, EDI (+1)
#
# Reads a byte into [EDI] and does EDI + 1
procedure ComRead8  {
    Call .ComReadAL
    EDI[0] = AL
    EDI + 1
}
procedure ComRead16 {
	Call .ComRead8
	Call .ComRead8
}
procedure ComRead32 {
	Call .ComRead8
	Call .ComRead8
	Call .ComRead8
	Call .ComRead8
}

# Input: AL
# Output: None
# Modifies: EDX, ESI
procedure ComWriteAL {
	+EAX
    ESI = ESP
    Call .ComWrite8
    # Is a local var, cant use Return(4). X# issues the return.
    # This also allows the function to preserve EAX.
    -EAX
}
procedure ComWriteAX {
    # Input: AX
    # Output: None
    # Modifies: EDX, ESI
    +EAX
    ESI = ESP
    Call .ComWrite16
    # Is a local var, cant use Return(4). X# issues the return.
    # This also allow the function to preserve EAX.
    -EAX
}
procedure ComWriteEAX {
    # Input: EAX
    # Output: None
    # Modifies: EDX, ESI
    +EAX
    ESI = ESP
    Call .ComWrite32
    # Is a local var, cant use Return(4). X# issues the return.
    # This also allow the function to preserve EAX.
    -EAX
}

procedure ComWrite8 {
	# Input: ESI
	# Output: None
	# Modifies: EAX, EDX
	#
	# Sends byte at [ESI] to com port and does esi + 1
	#
	# This sucks to use the stack, but x86 can only read and write ports from AL and
	# we need to read a port before we can write out the value to another port.
	# The overhead is a lot, but compared to the speed of the serial and the fact
	# that we wait on the serial port anyways, its a wash.
	#
	# This could be changed to use interrupts, but that then complicates
	# the code and causes interaction with other code. DebugStub should be
	# as isolated as possible from any other code.

	# Sucks again to use DX just for this, but x86 only supports
	# 8 bit address for literals on ports
	DX = .ComAddr
	DX + 5

	# Wait for serial port to be ready
	# Bit 5 (0x20) test for Transmit Holding Register to be empty.
Wait:
	AL = Port[DX]
	AL ?& $20
	if 0 goto Wait

	# Set address of port
	DX = $03F8
	# Get byte to send
	AL = ESI[0]
	# Send the byte
	Port[DX] = AL

	ESI++
}
procedure ComWrite16 {
	Call .ComWrite8
	Call .ComWrite8
}
procedure ComWrite32 {
	Call .ComWrite8
	Call .ComWrite8
	Call .ComWrite8
	Call .ComWrite8
}
procedure ComWriteX {
More:
	Call .ComWrite8
	ECX--
	if !0 goto More
}