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machine: avoid heap allocations in USB code 

This commit replaces most heap allocations in USB related code with
stack allocations. This is important for several reasons:

  - It avoids running the GC unnecessarily.
  - It reduces code size by 400-464 bytes.
  - USB code might be called from interrupt handlers. The heap may be in
    an inconsistent state when that happens if main thread code also
    performs heap allocations.

The last one is by far the most important one: not doing heap
allocations in interrupts is critical for correctness. But the code size
reduction alone should be worth it.

There are two heap allocations in USB related code left: in the function
receiveUSBControlPacket (SAMD21 and SAMD51). This heap allocation must
also be removed because it runs in an interrupt, but I've left that for
a future change.
bitcode-path
Ayke van Laethem 4 years ago
committed by Ron Evans
parent
80caf2dab2
commit
321488dcfe
1 changed files with 71 additions and 35 deletions
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  1. 106
      src/machine/usb.go

106
src/machine/usb.go
View File

@ -43,8 +43,8 @@ func NewDeviceDescriptor(class, subClass, proto, packetSize0 uint8, vid, pid, ve
}
// Bytes returns DeviceDescriptor data
func (d DeviceDescriptor) Bytes() []byte {
b := make([]byte, deviceDescriptorSize)
func (d DeviceDescriptor) Bytes() [deviceDescriptorSize]byte {
var b [deviceDescriptorSize]byte
b[0] = byte(d.bLength)
b[1] = byte(d.bDescriptorType)
b[2] = byte(d.bcdUSB)
@ -91,8 +91,8 @@ func NewConfigDescriptor(totalLength uint16, interfaces uint8) ConfigDescriptor
}
// Bytes returns ConfigDescriptor data.
func (d ConfigDescriptor) Bytes() []byte {
b := make([]byte, configDescriptorSize)
func (d ConfigDescriptor) Bytes() [configDescriptorSize]byte {
var b [configDescriptorSize]byte
b[0] = byte(d.bLength)
b[1] = byte(d.bDescriptorType)
b[2] = byte(d.wTotalLength)
@ -131,8 +131,8 @@ func NewInterfaceDescriptor(n, numEndpoints, class, subClass, protocol uint8) In
}
// Bytes returns InterfaceDescriptor data.
func (d InterfaceDescriptor) Bytes() []byte {
b := make([]byte, interfaceDescriptorSize)
func (d InterfaceDescriptor) Bytes() [interfaceDescriptorSize]byte {
var b [interfaceDescriptorSize]byte
b[0] = byte(d.bLength)
b[1] = byte(d.bDescriptorType)
b[2] = byte(d.bInterfaceNumber)
@ -167,8 +167,8 @@ func NewEndpointDescriptor(addr, attr uint8, packetSize uint16, interval uint8)
}
// Bytes returns EndpointDescriptor data.
func (d EndpointDescriptor) Bytes() []byte {
b := make([]byte, endpointDescriptorSize)
func (d EndpointDescriptor) Bytes() [endpointDescriptorSize]byte {
var b [endpointDescriptorSize]byte
b[0] = byte(d.bLength)
b[1] = byte(d.bDescriptorType)
b[2] = byte(d.bEndpointAddress)
@ -205,8 +205,8 @@ func NewIADDescriptor(firstInterface, count, class, subClass, protocol uint8) IA
}
// Bytes returns IADDescriptor data.
func (d IADDescriptor) Bytes() []byte {
b := make([]byte, iadDescriptorSize)
func (d IADDescriptor) Bytes() [iadDescriptorSize]byte {
var b [iadDescriptorSize]byte
b[0] = byte(d.bLength)
b[1] = byte(d.bDescriptorType)
b[2] = byte(d.bFirstInterface)
@ -235,8 +235,8 @@ func NewCDCCSInterfaceDescriptor(subtype, d0, d1 uint8) CDCCSInterfaceDescriptor
}
// Bytes returns CDCCSInterfaceDescriptor data.
func (d CDCCSInterfaceDescriptor) Bytes() []byte {
b := make([]byte, cdcCSInterfaceDescriptorSize)
func (d CDCCSInterfaceDescriptor) Bytes() [cdcCSInterfaceDescriptorSize]byte {
var b [cdcCSInterfaceDescriptorSize]byte
b[0] = byte(d.len)
b[1] = byte(d.dtype)
b[2] = byte(d.subtype)
@ -262,8 +262,8 @@ func NewCMFunctionalDescriptor(subtype, d0, d1 uint8) CMFunctionalDescriptor {
}
// Bytes returns the CMFunctionalDescriptor data.
func (d CMFunctionalDescriptor) Bytes() []byte {
b := make([]byte, cmFunctionalDescriptorSize)
func (d CMFunctionalDescriptor) Bytes() [cmFunctionalDescriptorSize]byte {
var b [cmFunctionalDescriptorSize]byte
b[0] = byte(d.bFunctionLength)
b[1] = byte(d.bDescriptorType)
b[2] = byte(d.bDescriptorSubtype)
@ -288,8 +288,8 @@ func NewACMFunctionalDescriptor(subtype, d0 uint8) ACMFunctionalDescriptor {
}
// Bytes returns the ACMFunctionalDescriptor data.
func (d ACMFunctionalDescriptor) Bytes() []byte {
b := make([]byte, acmFunctionalDescriptorSize)
func (d ACMFunctionalDescriptor) Bytes() [acmFunctionalDescriptorSize]byte {
var b [acmFunctionalDescriptorSize]byte
b[0] = byte(d.len)
b[1] = byte(d.dtype)
b[2] = byte(d.subtype)
@ -351,19 +351,51 @@ const cdcSize = iadDescriptorSize +
endpointDescriptorSize
// Bytes returns CDCDescriptor data.
func (d CDCDescriptor) Bytes() []byte {
var buf []byte
buf = append(buf, d.iad.Bytes()...)
buf = append(buf, d.cif.Bytes()...)
buf = append(buf, d.header.Bytes()...)
buf = append(buf, d.controlManagement.Bytes()...)
buf = append(buf, d.functionalDescriptor.Bytes()...)
buf = append(buf, d.callManagement.Bytes()...)
buf = append(buf, d.cifin.Bytes()...)
buf = append(buf, d.dif.Bytes()...)
buf = append(buf, d.out.Bytes()...)
buf = append(buf, d.in.Bytes()...)
return buf
func (d CDCDescriptor) Bytes() [cdcSize]byte {
var b [cdcSize]byte
offset := 0
iad := d.iad.Bytes()
copy(b[offset:], iad[:])
offset += len(iad)
cif := d.cif.Bytes()
copy(b[offset:], cif[:])
offset += len(cif)
header := d.header.Bytes()
copy(b[offset:], header[:])
offset += len(header)
controlManagement := d.controlManagement.Bytes()
copy(b[offset:], controlManagement[:])
offset += len(controlManagement)
functionalDescriptor := d.functionalDescriptor.Bytes()
copy(b[offset:], functionalDescriptor[:])
offset += len(functionalDescriptor)
callManagement := d.callManagement.Bytes()
copy(b[offset:], callManagement[:])
offset += len(callManagement)
cifin := d.cifin.Bytes()
copy(b[offset:], cifin[:])
offset += len(cifin)
dif := d.dif.Bytes()
copy(b[offset:], dif[:])
offset += len(dif)
out := d.out.Bytes()
copy(b[offset:], out[:])
offset += len(out)
in := d.in.Bytes()
copy(b[offset:], in[:])
offset += len(in)
return b
}
// MSCDescriptor is not used yet.
@ -633,7 +665,8 @@ func sendDescriptor(setup usbSetup) {
if setup.wLength < deviceDescriptorSize {
l = int(setup.wLength)
}
sendUSBPacket(0, dd.Bytes()[:l])
buf := dd.Bytes()
sendUSBPacket(0, buf[:l])
return
case usb_STRING_DESCRIPTOR_TYPE:
@ -669,7 +702,8 @@ func sendConfiguration(setup usbSetup) {
if setup.wLength == 9 {
sz := uint16(configDescriptorSize + cdcSize)
config := NewConfigDescriptor(sz, 2)
sendUSBPacket(0, config.Bytes())
configBuf := config.Bytes()
sendUSBPacket(0, configBuf[:])
} else {
iad := NewIADDescriptor(0, 2, usb_CDC_COMMUNICATION_INTERFACE_CLASS, usb_CDC_ABSTRACT_CONTROL_MODEL, 0)
@ -705,10 +739,12 @@ func sendConfiguration(setup usbSetup) {
sz := uint16(configDescriptorSize + cdcSize)
config := NewConfigDescriptor(sz, 2)
buf := make([]byte, 0, sz)
buf = append(buf, config.Bytes()...)
buf = append(buf, cdc.Bytes()...)
configBuf := config.Bytes()
cdcBuf := cdc.Bytes()
var buf [configDescriptorSize + cdcSize]byte
copy(buf[0:], configBuf[:])
copy(buf[configDescriptorSize:], cdcBuf[:])
sendUSBPacket(0, buf)
sendUSBPacket(0, buf[:])
}
}

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