mirror of
https://github.com/danbulant/Cosmos
synced 2026-05-19 20:39:01 +00:00
155 lines
4 KiB
Text
155 lines
4 KiB
Text
namespace DebugStub
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// optionally exclude this serial version
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! %ifndef Exclude_IOPort_Based_Serial
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// mComPortAddresses = 0x3F8, 0x2F8, 0x3E8, 0x2E8;
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// Currently hardcoded to COM1.
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var ComAddr = $03F8
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// All information relating to our serial usage should be documented in this comment.
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// http://wiki.osdev.org/Serial_ports
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//
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// We do not use IRQs for debugstub serial. This is becuase DebugStub (DS)
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// MUST be:
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// - As simple as possible
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// - Interact as minimal as possible wtih normal Cosmos code because
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// the debugstub must *always* work even if the normal code is fubarred
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//
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// The serial port that is used for DS should be 'hidden' from Cosmos main
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// so that Cosmos main pretends it does not exist.
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//
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// IRQs would create a clash/mix of code.
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// This does make the serial code in DebugStub inefficient, but its well worth
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// the benefits received by following these rules.
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//
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// Baud rate is set to 115200. Likely our code could not exceed this rate
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// anyways the way it is written and there are compatibility issues on some
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// hardware above this rate.
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//
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// We assume a minimum level of a 16550A, which should be no problem on any
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// common hardware today. VMWare emulates the 16550A
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//
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// We do not handle flow control for outbound data (DS --> DC).
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// The DebugConnector (DC, the code in the Visual Studio side) however is threaded
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// and easily should be able to receive data faster than we can send it.
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// Most things are transactional with data being sent only when asked for, but
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// with tracing we do send a data directly.
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//
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// Currently there is no inbound flow control either (DC --> DS)
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// For now we assume all commands in bound are 16 bytes or less to ensure
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// that they fit in the FIFO. Commands in DS must wait for a command ID ACK
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// before sending another command.
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// See notes in ProcessCommand.
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//
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// http://www.nondot.org/sabre/os/files/Communication/ser_port.txt
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// Todo Auto params
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// Todo ebp frame ptr auto etc
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function InitSerial {
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DX = .ComAddr
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// Disable interrupts
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BX = DX
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DX + 1
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AL = 0
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Port[DX] = AL
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// Enable DLAB (set baud rate divisor)
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DX = BX
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DX + 3
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AL = $80
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Port[DX] = AL
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// 0x01, 0x00 - 115200
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// 0x02, 0x00 - 57600
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// 0x03, 0x00 - 38400
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//
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// Set divisor (lo byte)
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DX = BX
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AL = $01
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Port[DX] = AL
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// hi byte
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DX = BX
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DX + 1
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AL = $00
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Port[DX] = AL
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// 8N1
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DX = BX
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DX + 3
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AL = $03
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Port[DX] = AL
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// Enable FIFO, clear them
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// Set 14-byte threshold for IRQ.
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// We dont use IRQ, but you cant set it to 0
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// either. IRQ is enabled/diabled separately
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DX = BX
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DX + 2
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AL = $C7
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Port[DX] = AL
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// 0x20 AFE Automatic Flow control Enable - 16550 (VMWare uses 16550A) is most common and does not support it
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// 0x02 RTS
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// 0x01 DTR
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// Send 0x03 if no AFE
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DX = BX
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DX + 4
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AL = $03
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Port[DX] = AL
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}
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// Modifies: AL, DX
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function ComReadAL {
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DX = .ComAddr
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DX + 5
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Wait:
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AL = Port[DX]
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AL ?& $01
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if 0 goto Wait
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DX = .ComAddr
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AL = Port[DX]
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}
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function ComWrite8 {
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// Input: ESI
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// Output: None
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// Modifies: EAX, EDX
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//
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// Sends byte at [ESI] to com port and does esi + 1
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//
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// This sucks to use the stack, but x86 can only read and write ports from AL and
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// we need to read a port before we can write out the value to another port.
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// The overhead is a lot, but compared to the speed of the serial and the fact
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// that we wait on the serial port anyways, its a wash.
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//
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// This could be changed to use interrupts, but that then complicates
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// the code and causes interaction with other code. DebugStub should be
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// as isolated as possible from any other code.
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// Sucks again to use DX just for this, but x86 only supports
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// 8 bit address for literals on ports
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DX = .ComAddr
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DX + 5
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// Wait for serial port to be ready
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// Bit 5 (0x20) test for Transmit Holding Register to be empty.
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Wait:
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AL = Port[DX]
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AL ?& $20
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if 0 goto Wait
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// Set address of port
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DX = $03F8
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// Get byte to send
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AL = ESI[0]
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// Send the byte
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Port[DX] = AL
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ESI++
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}
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! %endif
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